The history of the discovery of the periodic law and the periodic system of chemical elements. The history of the discovery of the periodic law and the periodic system of chemical elements by Dmitry Ivanovich Mendeleev The history of the creation of the periodic system of chemical elements
The discovery of the table of periodic chemical elements was one of the important milestones in the history of the development of chemistry as a science. The discoverer of the table was the Russian scientist Dmitry Mendeleev. An extraordinary scientist with a broad scientific outlook managed to combine all ideas about the nature of chemical elements into a single coherent concept.
M24.RU will tell you about the history of the discovery of the table of periodic elements, interesting facts related to the discovery of new elements and folk tales that surrounded Mendeleev and the table of chemical elements he created.
Table opening history
By the middle of the 19th century, 63 chemical elements had been discovered, and scientists around the world have repeatedly made attempts to combine all existing elements into a single concept. It was proposed to place the elements in order of increasing atomic mass and divide them into groups according to similar chemical properties.
In 1863, the chemist and musician John Alexander Newland proposed his theory, who proposed a layout of chemical elements similar to that discovered by Mendeleev, but the scientist’s work was not taken seriously by the scientific community due to the fact that the author was carried away by the search for harmony and the connection of music with chemistry.
In 1869, Mendeleev published his diagram of the periodic table in the Journal of the Russian Chemical Society and sent notice of the discovery to the world's leading scientists. Subsequently, the chemist repeatedly refined and improved the scheme until it acquired its usual appearance.
The essence of Mendeleev's discovery is that with increasing atomic mass, the chemical properties of elements change not monotonically, but periodically. After a certain number of elements with different properties, the properties begin to repeat. Thus, potassium is similar to sodium, fluorine is similar to chlorine, and gold is similar to silver and copper.
In 1871, Mendeleev finally combined the ideas into the periodic law. Scientists predicted the discovery of several new chemical elements and described their chemical properties. Subsequently, the chemist’s calculations were completely confirmed - gallium, scandium and germanium fully corresponded to the properties that Mendeleev attributed to them.
Tales about Mendeleev
There were many tales about the famous scientist and his discoveries. People at that time had little understanding of chemistry and believed that studying chemistry was something like eating soup from babies and stealing on an industrial scale. Therefore, Mendeleev’s activities quickly acquired a mass of rumors and legends.
One of the legends says that Mendeleev discovered the table of chemical elements in a dream. This is not the only case; August Kekule, who dreamed of the formula of the benzene ring, also spoke about his discovery. However, Mendeleev only laughed at the critics. “I’ve been thinking about it for maybe twenty years, and you say: I was sitting there and suddenly... done!” the scientist once said about his discovery.
Another story credits Mendeleev with the discovery of vodka. In 1865, the great scientist defended his dissertation on the topic “Discourse on the combination of alcohol with water,” and this immediately gave rise to a new legend. The chemist’s contemporaries chuckled, saying that the scientist “creates quite well under the influence of alcohol combined with water,” and subsequent generations already called Mendeleev the discoverer of vodka.
They also laughed at the scientist’s lifestyle, and especially at the fact that Mendeleev equipped his laboratory in the hollow of a huge oak tree.
Contemporaries also made fun of Mendeleev’s passion for suitcases. The scientist, during his involuntary inactivity in Simferopol, was forced to while away the time by weaving suitcases. Later, he independently made cardboard containers for the laboratory’s needs. Despite the clearly “amateur” nature of this hobby, Mendeleev was often called a “master of suitcases.”
Discovery of radium
One of the most tragic and at the same time famous pages in the history of chemistry and the appearance of new elements in the periodic table is associated with the discovery of radium. The new chemical element was discovered by the spouses Marie and Pierre Curie, who discovered that the waste remaining after the separation of uranium from uranium ore was more radioactive than pure uranium.
Since no one knew what radioactivity was at that time, rumor quickly attributed healing properties and the ability to cure almost all diseases known to science to the new element. Radium was included in food products, toothpaste, and face creams. The rich wore watches whose dials were painted with paint containing radium. The radioactive element was recommended as a means to improve potency and relieve stress.
Such “production” continued for twenty years - until the 30s of the twentieth century, when scientists discovered the true properties of radioactivity and found out how destructive the effect of radiation is on the human body.
Marie Curie died in 1934 from radiation sickness caused by long-term exposure to radium.
Nebulium and Coronium
The periodic table not only ordered the chemical elements into a single harmonious system, but also made it possible to predict many discoveries of new elements. At the same time, some chemical “elements” were recognized as non-existent on the basis that they did not fit into the concept of the periodic law. The most famous story is the “discovery” of the new elements nebulium and coronium.
While studying the solar atmosphere, astronomers discovered spectral lines that they were unable to identify with any of the chemical elements known on earth. Scientists suggested that these lines belong to a new element, which was called coronium (because the lines were discovered during the study of the “corona” of the Sun - the outer layer of the star’s atmosphere).
A few years later, astronomers made another discovery while studying the spectra of gas nebulae. The discovered lines, which again could not be identified with anything terrestrial, were attributed to another chemical element - nebulium.
The discoveries were criticized because there was no longer room in Mendeleev's periodic table for elements with the properties of nebulium and coronium. After checking, it was discovered that nebulium is ordinary terrestrial oxygen, and coronium is highly ionized iron.
The material was created based on information from open sources. Prepared by Vasily Makagonov @vmakagonov
The nineteenth century in the history of mankind is a century in which many sciences were reformed, including chemistry. It was at this time that Mendeleev's periodic system appeared, and with it the periodic law. It was he who became the basis of modern chemistry. The periodic system of D.I. Mendeleev is a systematization of elements that establishes the dependence of chemical and physical properties on the structure and charge of the atom of a substance.
Story
The beginning of the periodic period was laid by the book “The Correlation of Properties with the Atomic Weight of Elements,” written in the third quarter of the 17th century. It displayed the basic concepts of the known chemical elements (at that time there were only 63 of them). In addition, the atomic masses of many of them were determined incorrectly. This greatly interfered with the discovery of D.I. Mendeleev.
Dmitry Ivanovich began his work by comparing the properties of elements. First of all, he worked on chlorine and potassium, and only then moved on to working with alkali metals. Armed with special cards on which chemical elements were depicted, he repeatedly tried to assemble this “mosaic”: laying it out on his table in search of the necessary combinations and matches.
After much effort, Dmitry Ivanovich finally found the pattern he was looking for and arranged the elements in periodic rows. Having received as a result empty cells between the elements, the scientist realized that not all chemical elements were known to Russian researchers, and that it was he who must give this world the knowledge in the field of chemistry that had not yet been given by his predecessors.
Everyone knows the myth that the periodic table appeared to Mendeleev in a dream, and he collected the elements into a single system from memory. This is, roughly speaking, a lie. The fact is that Dmitry Ivanovich worked quite long and concentrated on his work, and it exhausted him greatly. While working on the system of elements, Mendeleev once fell asleep. When he woke up, he realized that he had not finished the table and rather continued filling in the empty cells. His acquaintance, a certain Inostrantsev, a university teacher, decided that the periodic table had been dreamed of by Mendeleev and spread this rumor among his students. This is how this hypothesis emerged.
Fame
Mendeleev's chemical elements are a reflection of the periodic law created by Dmitry Ivanovich back in the third quarter of the 19th century (1869). It was in 1869 that Mendeleev’s notification about the creation of a certain structure was read out at a meeting of the Russian chemical community. And in the same year, the book “Fundamentals of Chemistry” was published, in which Mendeleev’s periodic system of chemical elements was published for the first time. And in the book “The Natural System of Elements and Its Use to Indicate the Qualities of Undiscovered Elements,” D. I. Mendeleev first mentioned the concept of “periodic law.”
Structure and rules for placing elements
The first steps in creating the periodic law were taken by Dmitry Ivanovich back in 1869-1871, at that time he worked hard to establish the dependence of the properties of these elements on the mass of their atom. The modern version consists of elements summarized in a two-dimensional table.
The position of an element in the table carries a certain chemical and physical meaning. By the location of an element in the table, you can find out what its valence is and determine other chemical characteristics. Dmitry Ivanovich tried to establish a connection between elements, both similar in properties and differing.
He based the classification of chemical elements known at that time on valence and atomic mass. By comparing the relative properties of elements, Mendeleev tried to find a pattern that would unite all known chemical elements into one system. By arranging them based on increasing atomic masses, he still achieved periodicity in each of the rows.
Further development of the system
The periodic table, which appeared in 1969, has been refined more than once. With the advent of noble gases in the 1930s, it was possible to reveal a new dependence of elements - not on mass, but on atomic number. Later, it was possible to establish the number of protons in atomic nuclei, and it turned out that it coincides with the atomic number of the element. Scientists of the 20th century studied electronic energy. It turned out that it also affects periodicity. This greatly changed ideas about the properties of elements. This point was reflected in later editions of Mendeleev’s periodic table. Each new discovery of the properties and characteristics of elements fit organically into the table.
Characteristics of Mendeleev's periodic system
The periodic table is divided into periods (7 rows arranged horizontally), which, in turn, are divided into large and small. The period begins with an alkali metal and ends with an element with non-metallic properties.
Dmitry Ivanovich's table is vertically divided into groups (8 columns). Each of them in the periodic table consists of two subgroups, namely the main and secondary ones. After much debate, at the suggestion of D.I. Mendeleev and his colleague U. Ramsay, it was decided to introduce the so-called zero group. It includes inert gases (neon, helium, argon, radon, xenon, krypton). In 1911, scientists F. Soddy were asked to place indistinguishable elements, the so-called isotopes, in the periodic table - separate cells were allocated for them.
Despite the correctness and accuracy of the periodic system, the scientific community did not want to recognize this discovery for a long time. Many great scientists ridiculed the work of D.I. Mendeleev and believed that it was impossible to predict the properties of an element that had not yet been discovered. But after the supposed chemical elements were discovered (and these were, for example, scandium, gallium and germanium), the Mendeleev system and his periodic law became the science of chemistry.
Table in modern times
Mendeleev's periodic table of elements is the basis of most chemical and physical discoveries related to atomic-molecular science. The modern concept of an element was formed precisely thanks to the great scientist. The advent of Mendeleev's periodic system introduced fundamental changes in ideas about various compounds and simple substances. The creation of the periodic table by scientists had a huge impact on the development of chemistry and all sciences related to it.
Introduction
The periodic law and the Periodic Table of Chemical Elements by D.I. Mendeleev are the basis of modern chemistry. They refer to such scientific laws that reflect phenomena that actually exist in nature, and therefore will never lose their significance.
The periodic law and the discoveries made on its basis in various fields of natural science and technology are the greatest triumph of the human mind, evidence of ever deeper penetration into the most intimate secrets of nature, the successful transformation of nature for the benefit of man.
“It rarely happens that a scientific discovery turns out to be something completely unexpected, it is almost always anticipated, but subsequent generations, who use proven answers to all questions, often find it difficult to appreciate what difficulties it cost their predecessors.” DI. Mendeleev.
Purpose: To characterize the concept of a periodic system and the periodic law of elements, the periodic law and its rationale, to characterize the structures of the periodic system: subgroups, periods and groups. Study the history of the discovery of the periodic law and the periodic system of elements.
Objectives: Consider the history of the discovery of the periodic law and the periodic system. Define the periodic law and the periodic system. Analyze the periodic law and its rationale. The structure of the periodic table: subgroups, periods and groups.
The history of the discovery of the periodic law and the periodic system of chemical elements
The establishment of the atomic-molecular theory at the turn of the 19th – 19th centuries was accompanied by a rapid increase in the number of known chemical elements. In the first decade of the 19th century alone, 14 new elements were discovered. The record holder among the discoverers was the English chemist Humphry Davy, who in one year using electrolysis obtained 6 new simple substances (sodium, potassium, magnesium, calcium, barium, strontium). And by 1830, the number of known elements reached 55.
The existence of such a number of elements, heterogeneous in their properties, puzzled chemists and required ordering and systematization of the elements. Many scientists searched for patterns in the list of elements and achieved some progress. We can highlight three most significant works that challenged the priority of the discovery of the periodic law by D.I. Mendeleev.
In 1860, the first International Chemical Congress took place, after which it became clear that the main characteristic of a chemical element is its atomic weight. The French scientist B. De Chancourtois in 1862 was the first to arrange the elements in order of increasing atomic weights and arrange them in a spiral around a cylinder. Each turn of the spiral contained 16 elements, similar elements, as a rule, fell into vertical columns, although significant differences were also noted. De Chancourtois's work went unnoticed, but his idea of sorting elements in order of increasing atomic weights proved fruitful.
And two years later, guided by this idea, the English chemist John Newlands arranged the elements in a table and noticed that the properties of the elements were repeated periodically every seven numbers. For example, chlorine is similar in properties to fluorine, potassium is similar to sodium, selenium is similar to sulfur, etc. Newlands called this pattern the “law of octaves,” almost anticipating the concept of a period. But Newlands insisted that the length of the period (equal to seven) is constant, so his table contains not only the correct patterns, but also random pairs (cobalt - chlorine, iron - sulfur and carbon - mercury).
But the German scientist Lothar Meyer in 1870 plotted the dependence of the atomic volume of elements on their atomic weight and discovered a clear periodic dependence, and the length of the period did not coincide with the law of octaves and was a variable value.
All these works have much in common. De Chancourtois, Newlands and Meyer discovered the manifestation of periodic changes in the properties of elements depending on their atomic weight. But they were unable to create a unified periodic system of all elements, since many elements did not find their place in the patterns they discovered. These scientists also failed to draw any serious conclusions from their observations, although they felt that the numerous relationships between the atomic weights of elements were a manifestation of some general law.
This general law was discovered by the great Russian chemist Dmitri Ivanovich Mendeleev in 1869. Mendeleev formulated the periodic law in the form of the following basic principles:
1. Elements arranged according to atomic weight represent a clear periodicity of properties.
2. We should expect the discovery of many more unknown simple bodies, for example, elements similar to Al and Si with an atomic weight of 65 - 75.
3. The atomic weight of an element can sometimes be corrected by knowing its analogues.
Some analogies are revealed by the size of the weight of their atom. The first position was known even before Mendeleev, but it was he who gave it the character of a universal law, predicting on its basis the existence of elements that had not yet been discovered, changing the atomic weights of a number of elements and arranging some elements in the table contrary to their atomic weights, but in full accordance with their properties (mainly by valence). The remaining provisions were discovered only by Mendeleev and are logical consequences of the periodic law
The correctness of these consequences was confirmed by many experiments over the next two decades and made it possible to speak of the periodic law as a strict law of nature.
Using these provisions, Mendeleev compiled his own version of the periodic table of elements. The first draft of the table of elements appeared on February 17 (March 1, new style) 1869.
And on March 6, 1869, Professor Menshutkin made an official announcement about Mendeleev’s discovery at a meeting of the Russian Chemical Society.
The following confession was put into the mouth of the scientist: I see in a dream a table where all the elements are arranged as needed. I woke up and immediately wrote it down on a piece of paper - only in one place did a correction later turn out to be necessary.” How simple everything is in legends! It took more than 30 years of the scientist’s life to develop and correct it.
The process of discovering the periodic law is instructive and Mendeleev himself spoke about it this way: “The idea involuntarily arose that there must be a connection between mass and chemical properties. And since the mass of a substance, although not absolute, but only relative, is ultimately expressed in the form of atomic weights, it is necessary to look for a functional correspondence between the individual properties of elements and their atomic weights. You can’t look for anything, even mushrooms or some kind of addiction, except by looking and trying. So I began to select, writing on separate cards elements with their atomic weights and fundamental properties, similar elements and similar atomic weights, which quickly led to the conclusion that the properties of elements are periodically dependent on their atomic weight, and, doubting many ambiguities, I did not doubt for a minute the generality of the conclusion drawn, since it is impossible to allow accidents.”
In the very first periodic table, all elements up to and including calcium are the same as in the modern table, with the exception of the noble gases. This can be seen from a fragment of a page from an article by D.I. Mendeleev, containing the periodic table of elements.
If we proceed from the principle of increasing atomic weights, then the next elements after calcium should have been vanadium (A = 51), chromium (A = 52) and titanium (A = 52). But Mendeleev put a question mark after calcium, and then placed titanium, changing its atomic weight from 52 to 50. The unknown element, indicated by a question mark, was assigned an atomic weight A = 45, which is the arithmetic mean between the atomic weights of calcium and titanium. Then, between zinc and arsenic, Mendeleev left room for two elements that had not yet been discovered. In addition, he placed tellurium in front of iodine, although the latter has a lower atomic weight. With this arrangement of elements, all horizontal rows in the table contained only similar elements, and the periodicity of changes in the properties of the elements was clearly evident.
Over the next two years, Mendeleev significantly improved the system of elements. In 1871, the first edition of Dmitry Ivanovich’s textbook “Fundamentals of Chemistry” was published, which presented the periodic system in an almost modern form. In the table, 8 groups of elements were formed, the group numbers indicate the highest valence of the elements of those series that are included in these groups, and the periods become closer to modern ones, divided into 12 series. Now each period begins with an active alkali metal and ends with a typical nonmetal, halogen.
The second version of the system made it possible for Mendeleev to predict the existence of not 4, but 12 elements and, challenging the scientific world, with amazing accuracy he described the properties of three unknown elements, which he called ekaboron (eka in Sanskrit means “the same thing”), ekaaluminum and ekasilicon . Their modern names are Se, Ga, Ge.
The scientific world of the West was initially skeptical about the Mendeleev system and its predictions, but everything changed when in 1875 the French chemist P. Lecoq de Boisbaudran, examining the spectra of zinc ore, discovered traces of a new element, which he named gallium in honor of his homeland (Gallium - ancient Roman name for France)
The scientist managed to isolate this element in its pure form and study its properties. And Mendeleev saw that the properties of gallium coincided with the properties of eka-aluminium, which he predicted, and told Lecoq de Boisbaudran that he incorrectly measured the density of gallium, which should be equal to 5.9-6.0 g/cm3 instead of 4.7 g/cm3. Indeed, more careful measurements led to the correct value of 5.904 g/cm3.
In 1879, the Swedish chemist L. Nilsson, while separating rare earth elements obtained from the mineral gadolinite, isolated a new element and named it scandium. This turns out to be the ecaboron predicted by Mendeleev.
Final recognition of the periodic law of D.I. Mendeleev was achieved after 1886, when the German chemist K. Winkler, analyzing silver ore, obtained an element that he called germanium. It turns out to be ecasilicon.
Related information.
The Mendeleev family lived in a house on the steep, high bank of the Tobol River in Tobolsk, and the future scientist was born here. At that time, many Decembrists were serving exile in Tobolsk: Annenkov, Baryatinsky, Wolf, Kuchelbecker, Fonwiesen and others... They infected those around them with their courage and hard work. They were not broken by prison, hard labor, or exile. Mitya Mendeleev saw such people. In communication with them, his love for the Motherland and responsibility for its future were formed. The Mendeleev family had friendly and family relations with the Decembrists. D. I. Mendeleev wrote: “... venerable and respected Decembrists lived here: Fonvizen, Annenkov, Muravyov, close to our family, especially after one of the Decembrists, Nikolai Vasilyevich Basargin, married my sister Olga Ivanovna... Decembrist families , in those days they gave Tobolsk life a special imprint and endowed it with a secular upbringing. The legend about them still lives in Tobolsk.”
At the age of 15, Dmitry Ivanovich graduated from high school. His mother Maria Dmitrievna made a lot of efforts to ensure that the young man continued his education.
Rice. 4. Mother of D.I. Mendeleev - Maria Dmitrievna.
Mendeleev tried to enter the Medical-Surgical Academy in St. Petersburg. However, anatomy turned out to be beyond the strength of the impressionable young man, so Mendeleev had to change medicine to pedagogy. In 1850 he entered the Main Pedagogical Institute, where his father once studied. Only here Mendeleev felt a taste for learning and soon became one of the best.
At the age of 21, Mendeleev passed the entrance exams brilliantly. Dmitry Mendeleev's studies in St. Petersburg at the Pedagogical Institute were not easy at first. In his first year, he managed to get unsatisfactory grades in all subjects except mathematics. But in senior years, things went differently - Mendeleev’s average annual grade was four and a half (out of a possible five).
His thesis on the phenomenon of isomorphism was recognized as a candidate's dissertation. A talented student in 1855. was appointed teacher at the Richelieu gymnasium in Odessa. Here he prepared his second scientific work - “Specific Volumes”. This work was presented as a master's thesis. In 1857 After defending it, Mendeleev received the title of Master of Chemistry and became a private assistant professor at St. Petersburg University, where he lectured on organic chemistry. In 1859 he was sent abroad.
Mendeleev spent two years at various universities in France and Germany, but the most productive was his dissertation work in Heidelberg with the leading scientists of that time, Bunsen and Kirchhoff.
Undoubtedly, the scientist’s life was greatly influenced by the nature of the environment in which he spent his childhood. From his youth to his old age, he did everything and always in his own way. Starting with everyday trifles and continuing to the essential. Dmitry Ivanovich’s niece, N. Ya. Kapustin-Gubkina recalled: “He had his own favorite dishes, invented by him for himself... He always wore a wide cloth jacket without a belt of the style he himself invented... He smoked rolled cigarettes, rolling them himself...” He created an exemplary estate - and immediately abandoned it. He conducted remarkable experiments on the adhesion of liquids, and immediately left this field of science forever. And what scandals he threw at his superiors! Even in his youth, as a fledgling graduate of the Pedagogical Institute, he shouted at the director of the department, for which he was summoned to the minister himself, Abraham Sergeevich Norovatov. However, what does he care about the director of the department - he didn’t even take the synod into account. When he imposed a seven-year penance on him on the occasion of his divorce from Feoza Nikitishna, who had never come to terms with the uniqueness of his interests, Dmitry Ivanovich, six years before the due date, persuaded the priest in Kronstadt to marry him again. And what was the story of his balloon flight worth, when he forcibly seized a balloon belonging to the military department, expelling General Kovanko, an experienced aeronaut, from the basket... Dmitry Ivanovich did not suffer from modesty, on the contrary - “Modesty is the mother of all vices,” Mendeleev asserted.
The originality of Dmitry Ivanovich’s personality was observed not only in the scientist’s behavior, but also in his entire appearance. His niece N. Ya. Kapustina-Gubkina drew the following verbal portrait of the scientist: “A mane of long fluffy hair around a high white forehead, very expressive and very mobile... Clear blue, soulful eyes... Many found similarities in him with Garibaldi... When talking, he always gesticulated . Wide, fast, nervous movements of his hands always corresponded to his mood... The timbre of his voice was low, but sonorous and intelligible, but his tone varied greatly and often switched from low notes to high, almost tenor... When he talked about something he didn’t like , then winced, bent over, groaned, squeaked...” Mendeleev's favorite leisure activity for many years was making suitcases and frames for portraits. He purchased supplies for these works at Gostiny Dvor.
Mendeleev's originality set him apart from the crowd from his youth... While studying at a pedagogical institute, the blue-eyed Siberian, who did not have a penny to his name, unexpectedly for the gentlemen professors, began to show such sharpness of mind, such fury in work that he left all his colleagues far behind. It was then that the actual state councilor, a famous figure in public education, teacher, scientist, professor of chemistry, Alexander Abramovich Voskresensky, noticed and fell in love with him. Therefore, in 1867, Alexander Abramovich recommended his favorite student, thirty-three-year-old Dmitry Ivanovich Mendeleev, to the position of professor of general and inorganic chemistry at the Faculty of Physics and Mathematics at St. Petersburg University. In May 1868, the Mendeleevs gave birth to their beloved daughter Olga...
Thirty-three is the traditional age of feat: at thirty-three, according to the epic, Ilya Muromets got off the stove. But although in this sense the life of Dmitry Ivanovich was no exception, he himself could hardly sense that a sharp turn was taking place in his life. Instead of the courses of technical, or organic, or analytical chemistry that he had taught previously, he had to begin reading a new course, general chemistry.
Of course, it’s easier using the thumbnail method. However, when he started his previous courses, it was also not easy. Russian manuals either did not exist at all, or they existed, but were outdated. Chemistry is a new, young thing, and in youth everything becomes outdated quickly. Foreign textbooks, the latest ones, had to be translated by myself. He translated “Analytical Chemistry” by Gerard, “Chemical Technology” by Wagner. But nothing worthy was found in organic chemistry in Europe, even if you sit down and write. And he wrote. In two months, a completely new course based on new principles, thirty printed sheets. Sixty days of daily binge labor - twelve finished pages per day. Precisely on a day - he did not want to make his schedule dependent on such a trifle as the rotation of the globe around its axis, he did not get up from the table for thirty or forty hours.
Dmitry Ivanovich could not only work drunkenly, but also sleep drunkenly. Mendeleev's nervous system was extremely sensitive, his senses were heightened - almost all memoirists, without saying a word, report that he unusually easily, constantly broke into a scream, although, in essence, he was a kind person.
It is possible that the innate personality traits of Dmitry Ivanovich were explained by his late appearance in the family - he was the “last child,” the seventeenth child. And according to current concepts, the possibility of mutations in offspring increases with the age of the parents.
He began his first lecture on general chemistry like this:
“We clearly distinguish everything that we notice as a substance or as a phenomenon. Matter occupies space and has weight, but a phenomenon is something that happens in time. Each substance produces a variety of phenomena, and there is not a single phenomenon that occurs without substance. The variety of substances and phenomena cannot escape everyone’s attention. To discover legality, that is, simplicity and correctness in this diversity, means to study nature ... "
To discover legality, that is, simplicity, and correctness... Substance has weight... Substance... Weight... Substance... Weight...
He thought about it incessantly, no matter what he did. And what did he not do! Dmitry Ivanovich had enough time for everything. It would seem that he finally received the best chemical department in Russia, a state-owned apartment, the opportunity to live comfortably, without running around for extra money - so concentrate on the main thing, and everything else is on the side... I bought an estate of 400 dessiatines of land and a year later mortgaged experienced Paul, who studied the possibility of reversing the depletion of the earth using chemistry. One of the first in Russia.
A year and a half passed in an instant, and there was still no real system in general chemistry. This does not mean that Mendeleev taught his course completely haphazardly. He started with what is familiar to everyone - with water, with air, with coal, with salts. From the elements they contain. From the main laws according to which substances interact with each other.
Then he talked about the chemical relatives of chlorine - fluorine, bromine, iodine. This was the last lecture, the transcript of which he still managed to send to the printing house, where the second issue of the new book he had started was being typed.
The first issue, in pocket format, was printed in January 1869. The title page read: "Fundamentals of chemistry by D. Mendeleev" . No prefaces. The first, already published issue, and the second, which was in the printing house, were supposed to constitute, according to Dmitry Ivanovich’s plan, the first part of the course, and two more issues - the second part.
In January and the first half of February, Mendeleev gave lectures on sodium and other alkali metals, wrote the corresponding chapter of the second part "Fundamentals of Chemistry" - and got stuck.
In 1826, Jens Jakob Berzelius completed a study of 2000 substances and, on this basis, determined the atomic weight of three dozen chemical elements. For five of them, the atomic weight was determined incorrectly - for sodium, potassium, silver, boron and silicon. Berzelius made a mistake because he applied two incorrect assumptions: that an oxide molecule can contain only one metal atom and that an equal volume of gases contains an equal number of atoms. In fact, an oxide molecule can contain two or more metal atoms, and an equal volume of gases, according to Avogadro’s law, contains an equal number of not atoms, but molecules.
Until 1858, when the Italian Stanislao Cannizzaro, reinstating the law of his compatriot Avogadro, corrected the atomic weights of several elements, confusion reigned in the matter of atomic weights.
Only in 1860, at the chemical congress in Karlsruhe, after heated debates, the confusion was unraveled, Avogadro's law was finally restored to its rights and the unshakable foundations for determining the atomic weight of any chemical element were finally clarified.
By a happy coincidence, Mendeleev was on a business trip abroad in 1860, attended this congress and received a clear and distinct idea that atomic weight had now become an accurate and reliable numerical expression. Returning to Russia, Mendeleev began studying the list of elements, and drew attention to the periodicity of changes in valence of elements arranged in increasing order of atomic weights: valence H – 1, Li – 1, Be – 2, B – 3, C – 4, Mg – 2, N – 2, S – 2, F – 1, Na – 1, Al – 3, Si – 4, etc. Based on increases and decreases in valency, Mendeleev divided the elements into periods; The first period included only one hydrogen, followed by two periods of 7 elements each, then periods containing more than 7 elements. D, I, Mendeleev used these data not only to construct a graph, as Meyer and Chancourtois did, but also to construct a table similar to the Newlands table. Such a periodic table of elements is clearer and more visual than a graph, and, in addition, D, I, Mendeleev managed to avoid the mistake of Newlands, who insisted on equality of periods.
« I consider the decisive moment of my thought about the periodic law to be 1860 - the congress of chemists in Karlsruhe, in which I participated... The idea of the possibility of periodicity in the properties of elements with increasing atomic weight, in essence, was already presented to me internally." , - noted D.I. Mendeleev.
In 1865, he bought the Boblovo estate near Klin and got the opportunity to study agricultural chemistry, which he was then interested in, and relax there with his family every summer.
The “birthday” of D.I. Mendeleev’s system is usually considered February 18, 1869, when the first version of the table was compiled.
Rice. 5. Photo of D.I. Mendeleev in the year of the discovery of the periodic law.
63 chemical elements were known. Not all the properties of these elements have been studied well enough; even the atomic weights of some have been determined incorrectly or inaccurately. Is it a lot or a little - 63 elements? If we remember that we now know 109 elements, then, of course, this is not enough. But it is quite enough for one to notice the pattern of changes in their properties. With 30 or 40 known chemical elements, it would be unlikely that anything would be discovered. A certain minimum of open elements was needed. That is why Mendeleev's discovery can be characterized as timely.
Before Mendeleev, scientists also tried to subordinate all known elements to a certain order, classify them, and combine them into a system. It is impossible to say that their attempts were useless: they contained some grains of truth. All of them limited themselves to combining elements with similar chemical properties into groups, but did not find an internal connection between these “natural”, as they said then, groups of them.
In 1849, the prominent Russian chemist G. I. Hess became interested in the classification of elements. In the textbook “Foundations of Pure Chemistry,” he described four groups of nonmetal elements with similar chemical properties:
I Te C N
Br Se B P
Cl S Si As
F O
Hess wrote: “This classification is still very far from being natural, but it still connects elements and groups that are very similar, and with the expansion of our information it can be improved.”
Unsuccessful attempts to construct a system of chemical elements based on their atomic weights were made even before the congress in Karlsruhe, both by the British: in 1853 by Gladstone, in 1857 by Odling.
One of the attempts at classification was made in 1862 by the Frenchman Alexandre Emile Beguys de Chancourtois . He represented the system of elements in the form of a spiral line on the surface of a cylinder. There are 16 elements on each turn. Similar elements were located one below the other on the generatrix of the cylinder. When publishing his message, the scientist did not accompany it with the graph he had constructed, and none of the scientists paid attention to de Chancourtois’ work.
Rice. 6. “Tellurium screw” by de Chancourtois.
The German chemist Julius Lothar Meyer was more successful. In 1864, he proposed a table in which all known chemical elements were divided into six groups, according to their valency. In appearance, Meyer's table was a little similar to the future periodic table. He considered the volumes occupied by weight quantities of an element numerically equal to their atomic weights. It turned out that each such weight quantity of any element contains the same number of atoms. This meant that the ratio of the considered volumes of different atoms of these elements. Therefore, this characteristic of the element is called atomic volume.
Graphically, the dependence of the atomic volumes of elements on their atomic weights is expressed as a series of waves rising in sharp peaks at points corresponding to alkali metals (sodium, potassium, cesium). Each descent and rise to the peak corresponds to a period in the table of elements. In each period, the values of some physical characteristics, in addition to atomic volume, also naturally first decrease and then increase.
Rice. 7. Dependence of atomic volumes on atomic masses of elements, according to
L. Meyer.
Hydrogen, the element with the lowest atomic weight, was first on the list of elements. At that time it was generally accepted that the 101st period included one element. The 2nd and 3rd periods of the Meyer chart each included seven elements. These periods duplicated the Newlands octaves. However, in the next two periods the number of elements exceeded seven. Thus, Meyer showed where Newlands was wrong. The law of octaves could not be strictly followed for the entire list of elements; the last periods had to be longer than the first.
After 1860, the first attempt of this kind was made by another English chemist, John Alexander Reina Newlands. One after another, he compiled tables in which he tried to realize his idea. The last table is dated 1865. The scientist believed that everything in the world is subject to general harmony. It must be the same in both chemistry and music. Constructed in increasing order, the atomic weights of the elements are divided into octaves - into eight vertical rows, seven elements in each. Indeed, many elements with related chemical properties ended up in one horizontal line: in the first - halogens, in the second - alkali metals, and so on. But, unfortunately, quite a few strangers got into the ranks, and this spoiled the whole picture. Among the halogens, for example, there were cobalt with nickel and three platinoids. Among the alkaline earth minerals are vanadium and lead. The carbon family includes tungsten and mercury. In order to somehow unite related elements, Newlands had to disrupt the arrangement of elements in the order of atomic weights in eight cases. In addition, to make eight groups of seven elements, you need 56 elements, but 62 were known, and in some places he replaced one element with two at once. The result was complete arbitrariness. When Newlands reported his "Law of Octaves" At a meeting of the London Chemical Society, one of those present sarcastically remarked: hasn’t the venerable speaker tried to arrange the elements simply alphabetically and discover some kind of pattern?
All these classifications did not contain the main thing: they did not reflect the general, fundamental pattern of changes in the properties of elements. They created only the appearance of order in their world.
Mendeleev's predecessors, who noticed particular manifestations of the great pattern in the world of chemical elements, for various reasons were unable to rise to the great generalization and realize the existence of a fundamental law in the world. Mendeleev did not know much about the attempts of his predecessors to arrange chemical elements in order of increasing atomic masses and about the incidents that arose in this case. For example, he had almost no information about the work of Chancourtois, Newlands and Meyer.
Unlike Newlands, Mendeleev considered the main thing not so much atomic weights as chemical properties, chemical individuality. He thought about this constantly. Substance... Weight... Substance... Weight... No solutions came.
And then Dmitry Ivanovich found himself in severe time trouble. And it turned out very badly: not so much “now or never,” but either today, or the matter was postponed again for several weeks.
Long ago he made a promise to the Free Economic Society to go to the Tver province in February, examine the cheese factories there and present his thoughts on putting this matter in a modern way. The permission of the university authorities had already been sought for the trip. And the “vacation certificate” - the then travel certificate - had already been corrected. And the last parting note from the Secretary of the Free Economic Society Khodnev has been received. And there was nothing left to do but set off on the appointed voyage. The train on which he was to travel to Tver departed from the Moskovsky station on February 17, in the evening.
“In the morning, while still in bed, he invariably drank a mug of warm milk... Having gotten up and washed, he immediately went to his office and there he drank one, two, sometimes three large, mug-shaped cups of strong, not very sweet tea.” (from the memoirs of his niece N.Ya. Kapustina-Gubkina).
The trace of the cup, preserved on the back of Khodnev’s note, dated February 17, indicates that it was received early in the morning, before breakfast, probably brought by a messenger. And this, in turn, indicates that the thought of a system of elements did not leave Dmitry Ivanovich either day or night: next to the imprint of the cup, the leaf keeps visible traces of the invisible thought process that led to the great scientific discovery. In the history of science, this is a rare case, if not the only one.
Judging by the physical evidence, this is what happened. Having finished his mug and placing it on the first place he came across - on Khodnev’s letter, he immediately grabbed the pen and on the first piece of paper he came across, on the same letter from Khodnev, he wrote down the thought that flashed in his head. On the sheet of paper appeared, one under the other, the symbols of chlorine and potassium... Then sodium and boron, then lithium, barium, hydrogen... The pen wandered, as did the thought. Finally, he took a normal octam of blank paper - this piece of paper has also been preserved - and sketched on it, one under the other, in decreasing order, rows of symbols and atomic weights: at the top are the alkaline earths, below them are the halogens, below them is the oxygen group, below it is the nitrogen group, below it is the group carbon, etc. It was obvious to the eye how close the differences in atomic weights of elements of neighboring ranks were. Mendeleev could not have known then that the “uncertain zone” between obvious non-metals And metals contains elements - noble gases, the discovery of which will subsequently significantly modify the Periodic Table.
He was in a hurry, so every now and then he made mistakes and mistakes. Sulfur was assigned an atomic weight of 36, instead of 32. Subtracting them 65 (atomic weight of zinc) 39 (atomic weight of potassium), he received 27. But it’s not the little things that matter! He was carried by a high wave of intuition.
He believed in intuition. I used it quite consciously in a variety of situations in my life. Anna Ivanovna, Mendeleev’s wife wrote: “ If he
Some difficult, important life issue had to be resolved, he quickly entered with his light gait, said what was the matter, and asked to tell me my opinion based on the first impression. “Just don’t think, just don’t think,” he repeated. I spoke and this was the decision.”
However, nothing worked. The scribbled sheet again turned into a rebus. And time passed, in the evening we had to go to the station. He has already felt and felt the main thing. But this feeling certainly had to be given a clear logical form. You can imagine how, in despair or rage, he rushed around the office, looking at everything that was in it, looking for a way to quickly put the system together. Finally, he grabbed a stack of cards, opened his “Fundamentals” on the right page - where there was a list of simple bodies - and began to make an unprecedented deck of cards. Having made a deck of chemical cards, he began to play an unprecedented game of solitaire. Solitaire was clearly a challenge! The first six ranks lined up without any scandals. But then everything began to unravel.
Again and again Dmitry Ivanovich grabbed the pen and, with his rapid handwriting, scribbled columns of numbers on the sheet of paper. And again, in bewilderment, he gave up this activity and began to roll his cigarette and puff on it so much that his head became completely cloudy. Finally his eyes began to droop, he threw himself on the sofa and fell fast asleep. This was not unusual for him. This time he did not sleep for long - maybe a few hours, but maybe a few minutes. There is no exact information about this. He woke up from the fact that he saw his solitaire game in a dream, and not in the form in which he left it on the desk, but in another, more harmonious and logical one. And he immediately jumped to his feet and began to draw up a new table on a piece of paper.
Its first difference from the previous version was that the elements were now arranged not in order of decreasing, but in order of increasing atomic weights. The second is that the empty spaces inside the table were filled with question marks and atomic weights.
Rice. 8. Rough sketch compiled by D.I. Mendeleev during the discovery of the periodic law (during the course of playing “chemical solitaire”). February 17 (March 1), 1869.
For a long time, Dmitry Ivanovich’s story that he saw his table in a dream was treated as an anecdote. Finding anything rational in dreams was considered superstition. Nowadays science no longer puts a blind barrier between the processes occurring in the conscious and subconscious. And he sees nothing supernatural in the fact that a picture that did not emerge in the process of conscious deliberation was produced in finished form as a result of an unconscious process.
Mendeleev, convinced of the existence of an objective law to which all elements with diverse properties obey, followed a fundamentally different path.
Being a spontaneous materialist, he was looking for something material as a characteristic of elements, reflecting all the diversity of their properties. Taking the atomic weight of elements as such a characteristic, Mendeleev compared the groups known at that time according to the atomic weight of their members.
By writing the group of halogens (F = 19, Cl = 35.5, Br = 80, J = 127) under the group of alkali metals (Li = 7, Na = 23, K = 39, Rb = 85, Cs = 133) and placing it under them other groups of similar elements (in increasing order of their atomic weights), Mendeleev established that the members of these natural groups form a common regular series of elements; Moreover, the chemical properties of the elements that make up such a series are periodically repeated. Having placed all 63 elements known at that time into the total according to the value of atomic weights "periodic table" Mendeleev discovered that previously established natural groups organically entered this system, losing their previous artificial disunity. Later, Mendeleev formulated the periodic law he discovered as follows: “ The properties of simple bodies, as well as the forms and properties of compounds of elements, are periodically dependent on the values of the atomic weights of the elements.”
Mendeleev published the first version of the table of chemical elements expressing the periodic law in the form of a separate sheet entitled "An experiment on a system of elements based on their atomic weight and chemical similarity" and sent out this leaflet in March 1869. to many Russian and foreign chemists.
Rice. 9. “Experience of a system of elements based on their weight and chemical similarity.”
The first table is still very imperfect; it is far from the modern form of the periodic table. But this table turned out to be the first graphic illustration of the pattern discovered by Mendeleev: “Elements arranged according to their atomic weights represent a clear periodicity of properties” (“Relationship of properties with the atomic weight of elements” by Mendeleev). This article was the result of the scientist’s thoughts while working on the “System Experience...”. A report on the relationship discovered by Mendeleev between the properties of elements and their atomic weights was made on March 6 (18), 1869 at a meeting of the Russian Chemical Society. Mendeleev was not at this meeting. Instead of the absent author, his report was read by the chemist N. A. Menshutkin. A dry entry about the meeting on March 6 appeared in the minutes of the Russian Chemical Society: “N. Menshutkin reports on behalf of D. Mendeleev “the experience of a system of elements based on their atomic weight and chemical similarity.” Due to the absence of D. Mendeleev, the discussion of this issue was postponed until the next meeting.” N. Menshutkin’s speech was published in the Journal of the Russian Chemical Society (“Relationship of properties with the atomic weight of elements”). In the summer of 1871, Mendeleev summarized his numerous studies related to the establishment of the periodic law in his work "Periodic validity for chemical elements" . In the classic work “Fundamentals of Chemistry,” which went through 8 editions in Russian and several editions in foreign languages during Mendeleev’s lifetime, Mendeleev first presented inorganic chemistry on the basis of the periodic law.
When constructing the periodic system of elements, Mendeleev overcame great difficulties, since many elements had not yet been discovered, and of the 63 elements known by that time, nine had incorrectly determined atomic weights. When creating the table, Mendeleev corrected the atomic weight of beryllium, placing beryllium not in the same group with aluminum, as chemists usually did, but in the same group with magnesium. In 1870-71, Mendeleev changed the values of the atomic weights of indium, uranium, thorium, cerium and other elements, guided by their properties and specified place in the periodic table. Based on the periodic law, he placed tellurium in front of iodine and cobalt in front of nickel, so that tellurium would be in the same column with elements whose valency is 2, and iodine would be in the same column with elements whose valency is 1, although the atomic weights of these elements required the opposite location.
Mendeleev saw three circumstances that, in his opinion, contributed to the discovery of the periodic law:
Firstly, the atomic weights of most chemical elements were more or less accurately determined;
Secondly, a clear concept appeared about groups of elements with similar chemical properties (natural groups);
Thirdly, by 1869 the chemistry of many rare elements had been studied, without knowledge of which it would have been difficult to come to any generalization.
Finally, the decisive step towards the discovery of the law was that Mendeleev compared all the elements according to their atomic weights. Mendeleev's predecessors compared elements that were similar to each other. That is, elements of natural groups. These groups turned out to be unrelated. Mendeleev logically combined them in the structure of his table.
However, even after the enormous and careful work of chemists to correct atomic weights, in four places of the Periodic Table the elements “violate” the strict order of arrangement in increasing atomic weights. These are pairs of elements:
18 Ar(39.948) – 19 K (39.098); 27 Co(58.933) – 28 Ni(58.69);
52 Te(127.60) – 53 I(126.904) 90 Th(232.038) – 91 Pa(231.0359).
During the time of D.I. Mendeleev, such deviations were considered shortcomings of the Periodic Table. The theory of atomic structure put everything in its place: the elements are located absolutely correctly - in accordance with the charges of their nuclei. How then can we explain that the atomic weight of argon is greater than the atomic weight of potassium?
The atomic weight of any element is equal to the average atomic weight of all its isotopes, taking into account their abundance in nature. By chance, the atomic weight of argon is determined by the “heaviest” isotope (it is found in nature in larger quantities). In potassium, on the contrary, its “lighter” isotope (that is, an isotope with a lower mass number) predominates.
Mendeleev characterized the course of the creative process, which represents the discovery of the periodic law: “... the idea involuntarily arose that there must be a connection between mass and chemical properties. And since the mass of a substance, although not absolute, but only relative, it is necessary to look for a functional correspondence between the individual properties of elements and their atomic weights. You can’t look for anything, even mushrooms or some kind of addiction, except by looking and trying. So I began to select, writing on separate cards elements with their atomic weights and fundamental properties, similar elements and similar atomic weights, which quickly led to the conclusion that the properties of elements are periodically dependent on their atomic weight, and, doubting many ambiguities, I did not doubt for a minute the generality of the conclusion drawn, since it was impossible to admit an accident.”
The fundamental importance and novelty of the Periodic Law was as follows:
1. A connection was established between elements that were dissimilar in their properties. This connection lies in the fact that the properties of elements change smoothly and approximately equally as their atomic weight increases, and then these changes REPEAT PERIODICALLY.
2. In those cases when it seemed that some link was missing in the sequence of changes in the properties of elements, GAPS were provided in the Periodic Table that had to be filled with elements that had not yet been discovered.
Rice. 10. The first five periods of the Periodic Table of D. I. Mendeleev. Noble gases have not yet been discovered, so they are not shown in the table. Another 4 unknown elements at the time of creation of the table are marked with question marks. The properties of three of them were predicted by D.I. Mendeleev with high accuracy (part of the Periodic Table of the times of D.I. Mendeleev in a form more familiar to us).
The principle that D.I. Mendeleev used to predict the properties of yet unknown elements is depicted in Figure 11.
Based on the law of periodicity and practically applying the law of dialectics on the transition of quantitative changes into qualitative ones, Mendeleev pointed out already in 1869 the existence of four elements that had not yet been discovered. For the first time in the history of chemistry, the existence of new elements was predicted and their atomic weights were even approximately determined. At the end of 1870 Mendeleev, based on his system, described the properties of a still undiscovered group III element, calling it “eka-aluminium”. The scientist also suggested that the new element would be discovered using spectral analysis. Indeed, in 1875, the French chemist P.E. Lecoq de Boisbaudran, examining zinc blende with a spectroscope, discovered Mendeleev eka-aluminum in it. The exact coincidence of the expected properties of the element with the experimentally determined ones was the first triumph and a brilliant confirmation of the predictive power of the periodic law. Descriptions of the properties of “eka-aluminum” predicted by Mendeleev and the properties of gallium discovered by Boisbaudran are given in Table 1.
| Predicted by D.I. Mendeleev |
Installed by Lecoq de Boisbaudran (1875) |
| Ekaaluminium Ea Atomic weight about 68 Simple body, should be low fusible Density is close to 5.9 Atomic volume 11.5 Should not oxidize in air Should decompose water in red-hot heat Formulas of compounds: EaCl3, Ea2O3, Ea2(SO4)3 Should form alum Ea2(SO4)3 * M2SO4 * 24H2O, but more difficult than aluminum The oxide Ea2O3 should be easily reduced and produce a metal more volatile than aluminum, and therefore can be expected to be discovered by spectral analysis of EaCl3 - volatile. |
Atomic weight about 69.72 The melting point of pure gallium is 30 degrees C The density of solid gallium is 5.904, and liquid gallium is 6.095 Atomic volume 11.7 Slightly oxidizes only at red heat temperatures Decomposes water at high temperatures Compound formulas: GaСl3, Ga2О3, Ga2(SO4)3 Forms alum NH4Ga(SO4)2 * 12H2O Gallium is reduced from its oxide by calcination in a stream of hydrogen; discovered using spectral analysis Boiling point of GaCl3 215-220 degrees C |
In 1879 Swedish chemist L. Nilsson found the element scandium, which fully corresponds to the ekaboron described by Mendeleev; in 1886, the German chemist K. Winkler discovered the element germanium, corresponding to ekasilicon; in 1898, French chemists Pierre Curie and Marie Skłodowska Curie discovered polonium and radium. Mendeleev considered Winkler, Lecoq de Boisbaudran and Nilsson to be “strengtheners of the periodic law.”
Mendeleev's predictions also came true: trimarganese - modern rhenium, dicesium - francium, etc. were discovered.
After this, it became clear to scientists around the world that D.I. Mendeleev’s Periodic Table not only systematizes the elements, but is a graphic expression of the fundamental law of nature - the Periodic Law.
This law has predictive power. It made it possible to conduct a targeted search for new, not yet discovered elements. The atomic weights of many elements, previously determined insufficiently accurately, were subject to verification and clarification precisely because their erroneous values conflicted with the Periodic Law.
At one time, D.I. Mendeleev noted with disappointment: “...we do not know the reasons for periodicity.” He did not live to solve this mystery.
One of the important arguments in favor of the complex structure of atoms was the discovery of the periodic law of D. I. Mendeleev:
The properties of simple substances, as well as the properties and forms of compounds, periodically depend on the atomic masses of chemical elements.
When it was proven that the serial number of an element in a system is numerically equal to the charge of the nucleus of its atom, the physical essence of the periodic law became clear.
But why do the properties of chemical elements change periodically as the nuclear charge increases? Why is the system of elements built this way and not otherwise and why do its periods contain a strictly defined number of elements? There were no answers to these most important questions.
Logical reasoning predicted that if there is a relationship between chemical elements consisting of atoms, then the atoms have something in common and, therefore, they must have a complex structure.
The mystery of the periodic system of elements was completely solved when it was possible to understand the complex structure of the atom, the structure of its outer electron shells, and the laws of electron motion around a positively charged nucleus, in which almost the entire mass of the atom is concentrated.
All chemical and physical properties of a substance are determined by the structure of its atoms. The periodic law, discovered by Mendeleev, is a universal law of nature, because it is based on the law of atomic structure.
The founder of the modern doctrine of the atom is the English physicist Rutherford, who convincingly showed that almost all the mass and positively charged matter of an atom is concentrated in a small part of its volume. He called this part of the atom core. The positive charge of the nucleus is compensated by the electrons rotating around it. In this atomic model electrons resemble the planets of the solar system, which is why it received the name planetary. Subsequently, Rutherford was able to use experimental data to calculate nuclear charges. They turned out to be equal to the serial numbers of the elements in D.I. Mendeleev’s table. After the work of Rutherford and his students, Mendeleev’s periodic law received a clearer meaning and a slightly different formulation:
The properties of simple substances, as well as the properties and forms of compounds of elements, are periodically dependent on the charge of the nucleus of the atoms of the elements.
Thus, the serial number of a chemical element in the periodic table received a physical meaning.
In 1913, G. Moseley studied the X-ray radiation of a number of chemical elements in Rutherford's laboratory. For this purpose, he constructed the anode of the X-ray tube from materials consisting of certain elements. It turned out that the wavelengths of characteristic X-ray radiation increase with increasing serial number of the elements that make up the cathode. G. Moseley derived an equation relating wavelength and serial number Z:
This mathematical expression is now called Moseley's law. It makes it possible to determine the serial number of the element under study based on the measured wavelength of X-ray radiation.
The simplest atomic nucleus is the nucleus of the hydrogen atom. Its charge is equal and opposite in sign to the charge of the electron, and its mass is the smallest of all nuclei. The nucleus of the hydrogen atom was recognized as an elementary particle, and in 1920 Rutherford gave it the name proton . The mass of a proton is approximately one atomic mass unit.
However, the mass of all atoms, except hydrogen, numerically exceeds the charges of the atomic nuclei. Rutherford already assumed that in addition to protons, nuclei should contain some neutral particles with a certain mass. These particles were discovered in 1932 by Bothe and Becker. Chadwick established their nature and named neutrons . A neutron is an uncharged particle with a mass almost equal to the mass of a proton, i.e. Also 1 a. eat.
In 1932, the Soviet scientist D. D. Ivanenko and the German physicist Heisenberg independently developed the proton-neutron theory of the nucleus, according to which the nuclei of atoms consist of protons and neutrons.
Let us consider the structure of an atom of some element, for example, sodium, from the standpoint of the proton-neutron theory. The atomic number of sodium in the periodic system is 11, mass number 23. In accordance with the atomic number, the charge of the nucleus of a sodium atom is + 11. Therefore, the sodium atom has 11 electrons, the sum of their charges is equal to the positive charge of the nucleus. If the sodium atom loses one electron, then the positive charge will be one more than the sum of the negative charges of the electrons (10), and the sodium atom will become an ion with a charge of 1+. The charge of the nucleus of an atom is equal to the sum of the charges of 11 protons located in the nucleus, whose mass is 11 a. e.m. Since the mass number of sodium is 23 a. e.m., then the difference 23 – 11= 12 determines the number of neutrons in a sodium atom.
Protons and neutrons are called nucleons . The nucleus of a sodium atom consists of 23 nucleons, of which 11 are protons and 12 are neutrons. The total number of nucleons in the nucleus is written at the top left of the element symbol, and the number of protons at the bottom left, for example, Na.
All atoms of a given element have the same nuclear charge, that is, the same number of protons in the nucleus. The number of neutrons in the nuclei of atoms of elements can vary. Atoms that have the same number of protons and different numbers of neutrons in their nuclei are called isotopes .
Atoms of different elements whose nuclei contain the same number of nucleons are called isobars .
Science owes first of all to the great Danish physicist Niels Bohr the establishment of a real connection between the structure of the atom and the structure of the periodic table. He was the first to explain the true principles of periodic changes in the properties of elements. Bohr began by making Rutherford's model of the atom viable.
Rutherford's planetary model of the atom reflected the obvious truth that the main part of the atom is contained in an insignificantly small part of the volume - the atomic nucleus, and electrons are distributed in the rest of the volume of the atom. However, the nature of the motion of an electron in orbit around the nucleus of an atom contradicts the theory of motion of electric charges in electrodynamics.
Firstly, according to the laws of electrodynamics, an electron rotating around a nucleus must fall onto the nucleus as a result of energy loss through radiation. Secondly, when approaching the nucleus, the wavelengths emitted by the electron must continuously change, forming a continuous spectrum. However, atoms do not disappear, which means that electrons do not fall onto the nucleus, and the emission spectrum of atoms is not continuous.
If a metal is heated to the evaporation temperature, its vapor will begin to glow, and the vapor of each metal has its own color. The radiation of metal vapor decomposed by a prism forms a spectrum consisting of individual luminous lines. Such a spectrum is called line spectrum. Each line of the spectrum is characterized by a certain frequency of electromagnetic radiation.
In 1905, Einstein, explaining the phenomenon of the photoelectric effect, suggested that light propagates in the form of photons or energy quanta, which have a very specific meaning for each type of atom.
Bohr in 1913 introduced a quantum concept into Rutherford's planetary model of the atom and explained the origin of the line spectra of atoms. His theory of the structure of the hydrogen atom is based on two postulates.
First postulate:
The electron rotates around the nucleus, without emitting energy, in strictly defined stationary orbits that satisfy the quantum theory.
In each of these orbits, the electron has a certain energy. The farther the orbit is from the nucleus, the more energy the electron located on it has.
The motion of an object around a center in classical mechanics is determined by the angular momentum m´v´r, where m is the mass of the moving object, v is the speed of the object, r is the radius of the circle. According to quantum mechanics, the energy of this object can only have certain values. Bohr believed that the angular momentum of an electron in a hydrogen atom can only be equal to an integer number of action quanta. Apparently, this relationship was Bohr's guess; it was later derived mathematically by the French physicist de Broglie.
Thus, the mathematical expression of Bohr's first postulate is the equality:
(1)
In accordance with equation (1), the minimum radius of the electron's orbit, and, consequently, the minimum potential energy of the electron corresponds to a value of n equal to unity. The state of the hydrogen atom, which corresponds to the value n=1, is called normal or basic. A hydrogen atom whose electron is located in any other orbit corresponding to the values n = 2, 3, 4,¼ is called excited.
Equation (1) includes the electron velocity and orbital radius as unknowns. If you create another equation that includes v and r, you can calculate the values of these important characteristics of the electron in the hydrogen atom. This equation is obtained by taking into account the equality of centrifugal and centripetal forces acting in the “nucleus of a hydrogen atom – electron” system.
The centrifugal force is equal to . The centripetal force, which determines the attraction of the electron to the nucleus, according to Coulomb's law, is . Taking into account the equality of the charges of the electron and nucleus in the hydrogen atom, we can write:
(2)
Solving the system of equations (1) and (2) for v and r, we find:
(3)
Equations (3) and (4) make it possible to calculate the radii of orbits and electron velocities for any value of n. When n=1, the radius of the first orbit of the hydrogen atom is the Bohr radius, equal to 0.053 nm. The speed of an electron in this orbit is 2200 km/s. Equations (3) and (4) show that the radii of the electron orbits of the hydrogen atom are related to each other as the squares of natural numbers, and the speed of the electron decreases with increasing n.
Second postulate:
When moving from one orbit to another, an electron absorbs or emits a quantum of energy.
When an atom is excited, i.e., when an electron moves from an orbit closer to the nucleus to a more distant one, a quantum of energy is absorbed and, conversely, when an electron moves from a distant orbit to a near one, quantum energy E 2 – E 1 = hv is emitted. After finding the radii of the orbits and the energy of the electron on them, Bohr calculated the energy of photons and the corresponding lines in the line spectrum of hydrogen, which corresponded to the experimental data.
The number n, which determines the size of the radii of quantum orbits, the speed of movement of electrons and their energy, is called principal quantum number .
Subsequently, Sommerfeld improved Bohr's theory. He proposed that an atom could have not only circular, but also elliptical orbits of electrons, and on the basis of this he explained the origin of the fine structure of the hydrogen spectrum.
Rice. 12. The electron in the Bohr atom describes not only circular, but also elliptical orbits. Here's what they look like for different values l at P =2, 3, 4.
However, the Bohr-Sommerfeld theory of the structure of the atom combined classical and quantum mechanical concepts and, thus, was built on contradictions. The main disadvantages of the Bohr–Sommerfeld theory are as follows:
1. The theory is not able to explain all the details of the spectral characteristics of atoms.
2. It does not make it possible to quantitatively calculate the chemical bond even in such a simple molecule as the hydrogen molecule.
But the fundamental position was firmly established: the filling of electron shells in the atoms of chemical elements occurs starting from the third, M -shells not sequentially, gradually until full capacity (i.e., as it was with TO- And L - shells), but stepwise. In other words, the construction of electron shells is temporarily interrupted due to the fact that electrons belonging to other shells appear in the atoms.
These letters are designated as follows: n , l , m l , m s – and in the language of atomic physics are called quantum numbers. Historically, they were introduced gradually, and their emergence is largely associated with the study of atomic spectra.
So it turns out that the state of any electron in an atom can be written down with a special code, which is a combination of four quantum numbers. These are not just some abstract quantities used to record electronic states. On the contrary, they all have real physical content.
Number P is included in the formula for the capacity of the electron shell (2 P 2), i.e., this quantum number P corresponds to the number of the electronic shell; in other words, this number determines whether an electron belongs to a given electron shell.
Number P accepts only integer values: 1, 2, 3, 4, 5, 6, 7,..., corresponding respectively to the shells: K, L, M, N, O, P, Q.
Because the P is included in the formula for electron energy, then they say that the principal quantum number determines the total energy reserve of the electron in the atom.
Another letter of our alphabet - the orbital (side) quantum number - is denoted as l . It was introduced to emphasize the inequality of all electrons belonging to a given shell.
Each shell is divided into certain subshells, and their number is equal to the number of the shell. That is, K-shell ( P =1) consists of one subshell; L-shell ( P =2) – from two; M-shell ( P =3) – from three subshells...
And each subshell of this shell is characterized by a certain value l . The orbital quantum number also takes integer values, but starting from zero, i.e. 0, 1, 2, 3, 4, 5, 6... Thus, l always less P . It is easy to understand that when P =1 l =0; at n =2 l =0 and 1; at n = 3 l = 0, 1 and 2, etc. Number l , so to speak, has a geometric image. After all, the orbits of electrons belonging to one or another shell can be not only circular, but also elliptical.
Different meanings l and characterize different types of orbits.
Physicists love traditions and prefer old letter designations to designate electron subshells s ( l =0), p ( l =1), d ( l =2), f ( l =3). These are the first letters of German words that characterize the features of a series of spectral lines caused by electron transitions: sharp, main, blurred, fundamental.
Now we can briefly write down which electron subshells are contained in electron shells (Table 2).
Knowing how many electrons different electron subshells can accommodate helps determine the third and fourth quantum numbers - m l and m s, which are called magnetic and spin.
Magnetic quantum number m l closely related to l and determines, on the one hand, the direction of location of these orbits in space, and on the other, their number possible for a given l . From some regularities of atomic theory it follows that for a given l quantum number m l, takes 2 l +1 integer values: from – l to + l , including zero. For example, for l =3 this is the sequence m l we have: - 3, - 2, - 1, 0, +1, +2, +3, i.e. a total of seven values.
Why m l called magnetic? Each electron, rotating in orbit around the nucleus, essentially represents one turn of the winding through which electric current flows. A magnetic field arises, so each orbit in an atom can be considered as a flat magnetic sheet. When there is an external magnetic field, each electron orbit will interact with this field and strive to occupy a certain position in the atom.
The number of electrons in each orbit is determined by the value of the spin quantum number m s.
The behavior of atoms in strong inhomogeneous magnetic fields showed that each electron in an atom behaves like a magnet. And this indicates that the electron rotates around its own axis, like a planet in orbit. This property of an electron is called “spin” (translated from English as “rotate”). The rotational motion of the electron is constant and unchanging. The rotation of an electron is completely unusual: it cannot be slowed down, accelerated, or stopped. It is the same for all electrons in the world.
But although spin is a common property of all electrons, it also accounts for the differences between electrons in an atom.
Two electrons, rotating in the same orbit around a nucleus, have the same spin in magnitude, and yet they can differ in the direction of their own rotation. In this case, the sign of the angular momentum and the sign of the spin change.
Quantum calculation leads to two possible values of spin quantum numbers inherent in an electron in orbit: s=+ and s= - . There can be no other meanings. Therefore, in an atom, either only one or two electrons can rotate in each orbit. There can be no more.
Each electron subshell can accommodate a maximum of 2(2 l + 1) - electrons, namely (table 3):
From here, by simple addition, the capacities of successive shells are obtained.
The simplicity of the basic law to which the original infinite complexity of the structure of the atom was reduced is amazing. All the whimsical behavior of electrons in its outer shell, which controls all its properties, can be expressed unusually simply: There are not and cannot be two identical electrons in an atom. This law is known in science as the Pauli principle (named after the Swiss theoretical physicist).
Knowing the total number of electrons in an atom, which is equal to its atomic number in the Mendeleev system, you can “build” an atom: you can calculate the structure of its outer electron shell - determine how many electrons are in it and what kind of electrons they are in it.
As you grow Z similar types of electronic configurations of atoms repeat periodically. In essence, this is also a formulation of the periodic law, but in relation to the process of electron distribution among shells and subshells.
Knowing the law of atomic structure, we can now construct a periodic table and explain why it is built this way. Only one small terminological clarification is needed: those elements in the atoms of which the construction of s-, p-, d-, f-subshells occurs are usually called s-, p-, d-, f-elements, respectively.
The formula of an atom is usually written in the following form: the main quantum number is indicated by the corresponding number, the secondary quantum number is marked by a letter, and the number of electrons is marked at the top right.
The first period contains 1 s-elements - hydrogen and helium. The schematic notation for the first period is as follows: 1 s 2 . The second period can be depicted as follows: 2 s 2 2 p 6, i.e. it includes elements in which 2 s-, 2 p-subshells are filled. And the third (3 s-, 3p-subshells are built in it): 3 s 2 3p 6. Obviously, similar types of electronic configurations are repeated.
At the beginning of the 4th period there are two 4 s-elements, i.e., filling of the N-shell begins earlier than the construction of the M-shell is completed. It contains 10 more vacant places, which are filled by ten subsequent elements (3 d-elements). The filling of the M-shell has ended, the filling of the N-shell continues (with six 4 p-electrons). Therefore, the structure of the 4th period is as follows: 4 s 2 3 d 10 4 p 6. The fifth period is filled in similarly:
5 s 2 4 d 10 5 p 6 .
There are 32 elements in the sixth period. Its schematic notation is: 6 s 2 4 f 14 5 d 10 6 p 6.
And finally, the next, 7th period: 7 s 2 5 f 14 6 d 10 7 p 6. It should be kept in mind that not all elements of the 7th period are known yet.
This stepwise filling of the shells is a strict physical law. It turns out that instead of occupying the levels of the 3 d subshell, it is more profitable (from an energy point of view) for electrons to first occupy the levels of the 4 s subshell. It is these energy “swings” “more profitable - less profitable” that explain the situation that in chemical elements the filling of electron shells occurs in steps.
In the mid-20s. French physicist L. de Broglie expressed a bold idea: all material particles (including electrons) have not only material, but also wave properties. It was soon possible to show that electrons, like light waves, could also bend around obstacles.
Since an electron is a wave, its movement in an atom can be described using the wave equation. This equation was derived in 1926 by the Austrian physicist E. Schrödinger. Mathematicians call it a second-order partial differential equation. For physicists, this is the basic equation of quantum mechanics.
This is what the equation looks like:
+++ y = 0,
Where m– electron mass; r – the distance of the electron from the nucleus; e – electron charge; E– total electron energy, equal to the sum of kinetic and potential energy; Z– serial number of the atom (for the hydrogen atom it is 1); h– “quantum of action”; x , y , z – electron coordinates; y is the wave function (an abstract abstract quantity characterizing the degree of probability).
The degree of probability that an electron is located at a certain location in space around the nucleus. If y = 1, then the electron must really be in this very place; if y = 0, then there is no trace of an electron there.
The idea of the probability of finding an electron is central to quantum mechanics. And the value of the y (psi) function (more precisely, the square of its value) expresses the probability of an electron being at one or another point in space.
In a quantum mechanical atom there are no definite electron orbits, so clearly outlined in the Bohr model of the atom. The electron seems to be spread out in space in the form of a cloud. But the density of this cloud is different: as they say, where it is thick and where it is empty. A higher cloud density corresponds to a higher probability of finding an electron.
From the abstract quantum mechanical model of the atom, one can move on to the visual and visible model of the Bohr atom. To do this, you need to solve the Schrödinger equation. It turns out that the wave function is associated with three different quantities, which can only take on integer values. Moreover, the sequence of changes in these quantities is such that they cannot be anything other than quantum numbers. Main, orbital and magnetic. But they were introduced specifically to designate the spectra of various atoms. Then they very organically migrated to the Bohr model of the atom. This is scientific logic - even the most severe skeptic cannot undermine it.
All this means that solving the Schrödinger equation ultimately leads to the derivation of the sequence of filling the electron shells and subshells of atoms. This is the main advantage of the quantum mechanical atom over the Bohr atom. And the concepts familiar to the planetary atom can be reconsidered from the point of view of quantum mechanics. We can say that an orbit is a certain set of probable positions of a given electron in an atom. It corresponds to a certain wave function. Instead of the term “orbit” in modern atomic physics and chemistry the term “orbital” is used.
So, the Schrödinger equation is like a magic wand that eliminates all the shortcomings contained in the formal theory of the periodic table. Transforms "formal" into "factual".
In reality this is far from the case. Because the equation has an exact solution only for the hydrogen atom, the simplest of atoms. For the helium atom and subsequent ones, it is impossible to accurately solve the Schrödinger equation, since the interaction forces between the electrons are added. And taking into account their influence on the final result is a mathematical task of unimaginable complexity. It is inaccessible to human abilities; only high-speed electronic computers, performing hundreds of thousands of operations per second, can compare with it. And even then only on the condition that the calculation program is developed with numerous simplifications and approximations.
Over 40 years, the list of known chemical elements has increased by 19. And all 19 elements were synthesized, prepared artificially.
The synthesis of elements can be understood as obtaining from an element with a lower nuclear charge, a lower atomic number, an element with a higher atomic number. And the process of production itself is called a nuclear reaction. Its equation is written in the same way as the equation of an ordinary chemical reaction. On the left side are the reacting substances, on the right are the resulting products. The reactants in a nuclear reaction are the target and the bombarding particle.
The target can be almost any element of the periodic table (in free form or in the form of a chemical compound).
The role of bombarding particles is played by a-particles, neutrons, protons, deuterons (nuclei of the heavy isotope of hydrogen), as well as the so-called multiply charged heavy ions of various elements - boron, carbon, nitrogen, oxygen, neon, argon and other elements of the periodic table.
For a nuclear reaction to occur, the bombarding particle must collide with the nucleus of the target atom. If a particle has a high enough energy, it can penetrate so deeply into the nucleus that it merges with it. Since all the particles listed above, except the neutron, carry positive charges, when they merge with the nucleus, they increase its charge. And a change in the value of Z means the transformation of elements: the synthesis of an element with a new value of the nuclear charge.
To find a way to accelerate bombarding particles and give them high energy, sufficient for them to merge with nuclei, a special particle accelerator was invented and constructed - a cyclotron. Then they built a special factory for new elements - a nuclear rector. Its direct purpose is to generate nuclear energy. But since intense neutron fluxes always exist in it, they are easy to use for artificial fusion purposes. A neutron has no charge, and therefore it does not need (and is impossible) to be accelerated. On the contrary, slow neutrons turn out to be more useful than fast ones.
Chemists had to rack their brains and show real miracles of ingenuity to develop ways to separate tiny amounts of new elements from the target substance. Learn to study the properties of new elements when only a few atoms were available...
Through the work of hundreds and thousands of scientists, 19 new cells were filled in the periodic table. Four are within its old boundaries: between hydrogen and uranium. Fifteen - for uranium. Here's how it all happened...
4 places in the periodic table remained empty for a long time: cells No. 43, 61, 85 and 87.
These 4 elements were elusive. The efforts of scientists aimed at searching for them in nature remained unsuccessful. With the help of the periodic law, all other places in the periodic table were filled long ago - from hydrogen to uranium.
More than once, reports of the discovery of these four elements have appeared in scientific journals. But all these discoveries were not confirmed: each time an accurate check showed that an error had been made and random insignificant impurities were mistaken for a new element.
A long and difficult search finally led to the discovery of one of nature's elusive elements. It turned out that excesium No. 87 occurs in the decay chain of the natural radioactive isotope uranium-235. It is a short-lived radioactive element.
Rice. 13. Scheme of formation of element No. 87 – France. Some radioactive isotopes can decay in two ways, for example, through both a- and b-decay. This phenomenon is called a radioactive fork. All natural radioaction families contain forks.
Element 87 deserves to be discussed in more detail. Now in chemistry encyclopedias we read: francium (serial number 87) was discovered in 1939 by the French scientist Margarita Perey.
How did Perey manage to catch the elusive element? In 1914, three Austrian radiochemists - S. Meyer, W. Hess and F. Paneth - began studying the radioactive decay of the actinium isotope with mass number 227. It was known that it belongs to the actinouranium family and emits b-particles; hence its breakdown product is thorium. However, scientists had vague suspicions that actinium-227 in rare cases also emits a-particles. In other words, this is one example of a radioactive fork. During such a transformation, an isotope of element 87 should be formed. Meyer and his colleagues did indeed observe alpha particles. Further research was required, but it was interrupted by the First World War.
Margarita Perey followed the same path. But she had more sensitive instruments and new, improved methods of analysis at her disposal. That's why she was successful.
Francium is classified as an artificially synthesized element. But still, the element was first discovered in nature. This is an isotope of francium-223. Its half-life is only 22 minutes. It becomes clear why there is so little France on Earth. Firstly, due to its fragility, it does not have time to concentrate in any noticeable quantities, and secondly, the process of its formation itself is characterized by a low probability: only 1.2% of actinium-227 nuclei decay with the emission of a-particles.
In this regard, it is more profitable to prepare francium artificially. 20 isotopes of francium have already been obtained, and the longest-lived of them is francium-223. Working with very small quantities of francium salts, chemists were able to prove that its properties are extremely similar to cesium.
By studying the properties of atomic nuclei, physicists came to the conclusion that stable isotopes cannot exist for elements with atomic numbers 43, 61, 85 and 87. They can only be radioactive, have short half-lives and must disappear quickly. Therefore, all these elements were created artificially by man. The paths for the creation of new elements were indicated by the periodic law. Element 43 was the first artificially created.
The nucleus of element 43 should have 43 positive charges and 43 electrons orbiting the nucleus. The empty space for element 43, located in the middle of the fifth period, has manganese in the fourth period and rhenium in the sixth. Therefore, the chemical properties of element 43 should be similar to those of manganese and rhenium. To the left of cell 43 is molybdenum No. 42, to the right is ruthenium No. 44. Therefore, to create element 43, it is necessary to increase the number of charges in the nucleus of an atom that has 42 charges by one more elementary charge. Therefore, to synthesize a new element 43, it is necessary to take molybdenum as a starting material. The lightest element, hydrogen, has one positive charge. So, it can be expected that element 43 can be obtained from a nuclear reaction between molybdenum and a proton.
Rice. 14. Scheme for the synthesis of element No. 43 – technetium.
The properties of element 43 should be similar to those of manganese and rhenium, and in order to detect and prove the formation of this element, it is necessary to use chemical reactions similar to those by which chemists determine the presence of small quantities of manganese and rhenium.
This is how the periodic table makes it possible to chart the path for the creation of artificial elements.
In exactly the same way, the first artificial chemical element was created in 1937. It received the significant name of technetium - the first element produced technically, artificially. This is how the synthesis of technetium was carried out. The molybdenum plate was subjected to intense bombardment by nuclei of the heavy isotope of hydrogen - deuterium, which were accelerated in a cyclotron to enormous speed.
Heavy hydrogen nuclei, which received very high energy, penetrated into the molybdenum nuclei. After irradiation in a cyclotron, the molybdenum plastic was dissolved in acid. An insignificant amount of a new radioactive substance was isolated from the solution using the same reactions that are necessary for the analytical determination of manganese (an analogue of element 43). This was the new element - technetium. They correspond exactly to the position of the element in the periodic table.
Now technetium has become quite accessible: it is formed in fairly large quantities in nuclear reactors. Technetium has been well studied and is already in practical use.
The method by which element 61 was created is very similar to the method by which technetium is produced. Element 61 was isolated only in 1945 from fragmentation elements formed in a nuclear reactor as a result of the fission of uranium.
Rice. 15. Scheme for the synthesis of element No. 61 – promethium.
The element received the symbolic name “promethium”. This name was not given to him lightly. It symbolizes the dramatic path of science stealing nuclear fission energy from nature and mastering this energy (according to legend, the titan Prometheus stole fire from the sky and gave it to people; for this he was chained to a rock and a huge eagle tormented him daily), but it also warns people against the terrible war danger.
Promethium is now obtained in considerable quantities: it is used in atomic batteries - direct current sources that can operate without interruption for many years.
The heaviest halogen, ekaiod, element 85, was synthesized in a similar way. It was first obtained by bombarding bismuth (No. 83) with helium nuclei (No. 2), accelerated in a cyclotron to high energies. The new element is named astatine (unstable). It is radioactive and disappears quickly. Its chemical properties also turned out to correspond exactly to the periodic law. It is similar to iodine.
Rice. 16. Scheme for the synthesis of element No. 85 – astatine.
Transuranic elements are artificially synthesized chemical elements located in the periodic table after uranium. How many more of them will be able to be synthesized in the future, no one can definitely answer yet.
Uranium was the last element in the natural series of chemical elements for 70 long years.
And all this time, scientists were naturally worried about the question: do elements heavier than uranium exist in nature? Dmitry Ivanovich believed that if uranium elements could ever be discovered in the bowels of the earth, then their number should be limited. After the discovery of radioactivity, the absence of such elements in nature was explained by the fact that their half-lives are short and they all decayed and turned into lighter elements a long time ago, in the very early stages of the evolution of our planet. But uranium, which turned out to be radioactive, had such a long lifespan that it has survived to this day. Why couldn’t nature give at least the closest transurans an equally generous time to exist? There have been many reports of the discovery of supposedly new elements within the system - between hydrogen and uranium, but almost never have scientific journals written about the discovery of transuraniums. Scientists only argued about the reason for the break of the periodic table on uranium.
Only nuclear fusion made it possible to establish interesting circumstances that previously could not even be suspected.
The first studies on the synthesis of new chemical elements were aimed at the artificial production of transuraniums. The first artificial transuranium element was talked about three years before technetium appeared. The stimulating event was the discovery of the neutron. an elementary particle, devoid of charge, had enormous penetrating power, could reach the atomic nucleus without encountering any obstacles, and cause transformations of various elements. Neutrons began to be fired at targets made from a wide variety of substances. The pioneer of research in this area was the outstanding Italian physicist E. Fermi.
Uranium irradiated with neutrons exhibited unknown activity with a short half-life. Uranium-238, having absorbed a neutron, turns into an unknown isotope of the element uranium-239, which is b-radioactive and should turn into an isotope of an element with atomic number 93. A similar conclusion was made by E. Fermi and his colleagues.
In fact, it took a lot of effort to prove that the unknown activity actually corresponded to the first transuranium element. Chemical operations led to the conclusion: the new element is similar in properties to manganese, i.e. it belongs to the VII b-subgroup. This argument turned out to be impressive: at that time (in the 30s) almost all chemists believed that if transuranium elements existed, then at least the first of them would be similar d-elements from previous periods. This was an error that undoubtedly affected the history of the discovery of elements heavier than uranium.
In short, in 1934, E. Fermi confidently announced the synthesis of not only element 93, to which he gave the name “ausonium,” but also its right neighbor on the periodic table, “hesperia” (No. 94). The latter was a product of the b-decay of ausonium:
There were scientists who “pulled” this chain even further. Among them: German researchers O. Hahn, L. Meitner and F. Strassmann. In 1937 they were already talking about element No. 97 as something real:
But none of the new elements were obtained in any noticeable quantities or isolated in free form. Their synthesis was judged by various indirect signs.
Ultimately, it turned out that all these ephemeral substances, taken for transuranium elements, are in fact elements belonging ... to the middle of the periodic table, that is, artificial radioactive isotopes of long-known chemical elements. This became clear when O. Hahn and F. Strassmann made one of the greatest discoveries of the 20th century on December 22, 1938. – discovery of uranium fission under the influence of slow neutrons. Scientists have irrefutably established that uranium irradiated with neutrons contains isotopes of barium and lanthanum. They could be formed only on the assumption that neutrons seem to break up uranium nuclei into several smaller fragments.
The fission mechanism was explained by L. Meitner and O. Frisch. The so-called droplet model of the nucleus already existed: the atomic nucleus became like a drop of liquid. If a drop is given enough energy and excited, it can split into smaller drops. Likewise, a nucleus brought into an excited state by a neutron can disintegrate and split into smaller parts - the nuclei of atoms of lighter elements.
In 1940, Soviet scientists G.N. Flerov and K.A. Petrzhak proved that uranium fission can occur spontaneously. Thus, a new type of radioactive transformation found in nature was discovered, the spontaneous fission of uranium. This was an extremely important discovery.
However, it is wrong to declare research on transuraniums in the 1930s erroneous.
Uranium has two main natural isotopes: uranium-238 (significantly predominant) and uranium-235. The second one is mainly fissioned under the influence of slow neutrons, while the first one, absorbing a neutron, only turns into a heavier isotope - uranium-239, and this absorption is more intense, the faster the bombarding neutrons. Therefore, in the first attempts to synthesize transuraniums, the effect of neutron moderation led to the fact that when a target made of natural uranium containing and was “fired”, the fission process prevailed.
But uranium-238, which absorbed a neutron, was bound to give rise to the chain of formation of transuranium elements. It was necessary to find a reliable way to trap the atoms of element 93 in a complex mess of fission fragments. Relatively smaller in mass, these fragments during the bombardment of uranium should have flown over greater distances (have a longer path length) than the very massive atoms of element 93.
The American physicist E. MacMillan, who worked at the University of California, based his experiments on these considerations. In the spring of 1939, he began to carefully study the distribution of uranium fission fragments along the path lengths. He managed to separate a small portion of fragments with a small range. It was in this portion that he discovered traces of a radioactive substance with a half-life of 2.3 days and high radiation intensity. Such activity was not observed in other fractions of fragments. McMillan was able to show that this substance X is a decay product of the isotope uranium-239:
The chemist F. Ableson joined the work. It turned out that a radioactive substance with a half-life of 2.3 days can be chemically separated from uranium and thorium and has nothing to do with rhenium. Thus the assumption that element 93 should be ekarenium collapsed.
The successful synthesis of neptunium (the new element was named after the planet of the solar system) was announced by the American journal “Physical Review” in early 1940. Thus began the era of the synthesis of transuranium elements, which turned out to be very important for the further development of Mendeleev’s doctrine of periodicity.
Rice. 17. Scheme for the synthesis of element No. 93 - neptunium.
Even the periods of the longest-lived isotopes of transuranium elements, as a rule, are significantly shorter than the age of the Earth, and therefore their existence in nature is currently practically excluded. Thus, the reason for the break in the natural series of chemical elements on uranium - element 92 is clear.
Neptunium was followed by plutonium. It was synthesized by a nuclear reaction:
winter 1940 – 1941 American scientist G. Seaborg and his colleagues (several new transuranium elements were subsequently synthesized in G. Seaborg’s laboratory). But the most important isotope of plutonium turned out to have a half-life of 24,360 years. In addition, plutonium-239 fissions much more intensely under the influence of slow neutrons than
Rice. 18. Scheme for the synthesis of element No. 94 - plutonium.
In the 40s three more elements heavier than uranium were synthesized: americium (in honor of America), curium (in honor of M. and P. Curie) and berkelium (in honor of Berkeley in California). The target in nuclear reactors was plutonium-239, bombarded by neutrons and a-particles, and americium (its irradiation led to the synthesis of berkelium):
.
50s began with the synthesis of californium (No. 98). It was obtained when the long-lived isotope curium-242 was accumulated in significant quantities and a target was made from it. Nuclear reaction: 
led to the synthesis of a new element 98.
To move towards elements 99 and 100, care had to be taken to accumulate weights of berkelium and californium. The bombardment of targets made from them with a-particles provided grounds for synthesizing new elements. But the half-lives (hours and minutes) of the synthesized isotopes of elements 97 and 98 were too short, and this turned out to be an obstacle to their accumulation in the required quantities. Another way was also proposed: long-term irradiation of plutonium with an intense neutron flux. But we would have to wait for the results for many years (to obtain one of the berkelium isotopes in its pure form, the plutonium target was irradiated for 6 years!). There was only one way to significantly reduce the synthesis time: to sharply increase the power of the neutron beam. This turned out to be impossible in laboratories.
A thermonuclear explosion came to the rescue. On November 1, 1952, the Americans exploded a thermonuclear device on Eniwetak Atoll in the Pacific Ocean. Several hundred kilograms of soil were collected from the explosion site and samples were examined. As a result, it was possible to discover isotopes of elements 99 and 100, named respectively einsteinium (in honor of A. Einstein) and fermium (in honor of E. Fermi).
The neutron flux generated during the explosion turned out to be very powerful that the uranium-238 nuclei were able to absorb a large number of neutrons in a very short period of time. These superheavy isotopes of uranium, as a result of chains of successive decays, turned into isotopes of einsteinium and fermium (Figure 19).
|
|
Rice. 19. Scheme of synthesis of elements No. 99 – einsteinium and No. 100 – fermium.
Mendeleevium is the name given to chemical element No. 101, synthesized by American physicists led by G. Seaborg in 1955. The authors of the synthesis named the new element “in honor of the merits of the great Russian chemist, who was the first to use the periodic system to predict the properties of undiscovered chemical elements.” Scientists managed to accumulate enough einsteinium to prepare a target from it (the amount of einsteinium was measured in a billion atoms); By irradiating it with a-particles, it was possible to calculate the synthesis of nuclei of element 101 (Figure 20):
Rice. 20. Scheme for the synthesis of element No. 101 - mendeleevium.
The half-life of the resulting isotope turned out to be much longer than theorists expected. And although only a few mendeleevium atoms were obtained as a result of the synthesis, it turned out to be possible to study their chemical properties using the same methods that were used for previous transuraniums.
A worthy assessment of the periodic law was given by William Razmay, who argued that the periodic law is a true compass for researchers.
| |
It is impossible to study chemistry except on the basis of this omnipresent law. How ridiculous a chemistry textbook would look without the periodic table! You need to understand how different elements are related to each other and why they are so connected. Only then will the periodic table turn out to be a rich repository of information about the properties of elements and their compounds, a repository that little can compare with.
An experienced chemist, just by looking at the place occupied by any element in a system, can tell a lot about it: whether the element is a metal or a non-metal; whether or not it forms compounds with hydrogen - hydrides; what oxides are characteristic of this element; what valencies it can exhibit when entering into chemical compounds; which compounds of this element will be stable, and which, on the contrary, will be fragile; From what compounds and in what way is it most convenient and profitable to obtain this element in free form. And if a chemist is able to extract all this information from the periodic table, then this means that he has mastered it well.
The periodic table is the basis for obtaining new materials and substances with new, unusual, predetermined properties, substances that are unknown to nature. They are now being created in large quantities. It also became a guiding thread for the synthesis of semiconductor materials. Using many examples, scientists have discovered that compounds of elements that occupy certain places in the periodic table (mainly in its groups III – V) have or should have the best semiconductor properties.
It is impossible to set the task of obtaining new alloys while ignoring the periodic table. After all, the structure and properties of alloys are determined by the position of the metals in the table. Currently, thousands of different alloys are known.
Perhaps in any branch of modern chemistry one can notice a reflection of the periodic law. But it is not only chemists who bow their heads before his greatness. In the difficult and fascinating task of synthesizing new elements, it is impossible to do without the periodic law. A gigantic natural process of synthesis of chemical elements occurs in stars. Scientists call this process nucleosynthesis.
So far, scientists have no idea in what exact ways, as a result of what successive nuclear reactions, the chemical elements known to us were formed. There are many hypotheses of nucleosynthesis, but there is no complete theory yet. But we can say with confidence that even the most timid assumptions about the paths of origin of elements would be impossible without taking into account the sequential arrangement of elements in the periodic table. The laws of nuclear periodicity, structure and properties of atomic nuclei underlie various nucleosynthesis reactions.
It would take a long time to list those areas of human knowledge and practice where the Great Law and the system of elements play an important role. And, to tell the truth, we do not even imagine the full scale of Mendeleev’s doctrine of periodicity. Many times it will flash its unexpected facets to scientists.
Mendeleev is undoubtedly one of the world's greatest chemists. Although more than a hundred years have passed since his law, no one knows when the entire content of the famous periodic table will be fully understood.
Rice. 21. Photo by Dmitry Ivanovich Mendeleev.
Rice. 22. Russian Chemical Society under the chairmanship
1. Petryanov I.V., Trifonov D.N. “The Great Law”
Moscow, “Pedagogy”, 1984
2. Kedrov B. M. “Forecasts of D. I. Mendeleev in atomism”
Moscow, Atomizdat, 1977
3. Agafoshin N. P. “Periodic law and the periodic system of elements of D. I. Mendeleev” Moscow, “Enlightenment”, 1973
4. "D. I. Mendeleev in the memoirs of his contemporaries" Moscow, "Atomizdat", 1973.
5. Volkov V. A. biographical reference book “Outstanding Chemists of the World” Moscow, “Higher School”, 1991
6. Bogolyubova L.N. “Biographies of great chemists” Moscow, “Enlightenment”, 1997
7. Ivanova L. F., Egorova E. N. desktop encyclopedia “Everything about everything” Moscow, “Mnemosyne”, 2001
8. Summ L.B. children's encyclopedia “I explore the world. Chemistry" Moscow, "Olympus", 1998
Everything material that surrounds us in nature, be it space objects, ordinary earthly objects or living organisms, consists of substances. There are many varieties of them. Even in ancient times, people noticed that they were able not only to change their physical state, but also to transform into other substances endowed with different properties compared to the original ones. But people did not immediately understand the laws according to which such transformations of matter occur. In order to do this, it was necessary to correctly identify the basis of the substance and classify the elements existing in nature. This became possible only in the middle of the 19th century with the discovery of the periodic law. The history of its creation D.I. The Mendeleevs were preceded by many years of work, and the formation of this type of knowledge was facilitated by the centuries-old experience of all mankind.
When were the foundations of chemistry laid?
Craftsmen of ancient times were quite successful in casting and melting various metals, knowing many secrets of their transmutation. They passed on their knowledge and experience to their descendants, who used them until the Middle Ages. It was believed that it was quite possible to transform base metals into valuable ones, which, in fact, was the main task of chemists until the 16th century. In essence, such an idea also contained the philosophical and mystical ideas of ancient Greek scientists that all matter is built from certain “primary elements” that can be transformed into one another. Despite the apparent primitiveness of this approach, it played a role in the history of the discovery of the Periodic Law.
Panacea and white tincture
While searching for the fundamental principle, alchemists firmly believed in the existence of two fantastic substances. One of them was the legendary philosopher's stone, also called the elixir of life or panacea. It was believed that such a remedy was not only a fail-safe way to transform mercury, lead, silver and other substances into gold, but also served as a miraculous universal medicine that healed any human ailment. Another element, called white tincture, was not so effective, but was endowed with the ability to convert other substances into silver.
Telling the background to the discovery of the periodic law, it is impossible not to mention the knowledge accumulated by alchemists. They personified an example of symbolic thinking. Representatives of this semi-mystical science created a certain chemical model of the world and the processes occurring in it at the cosmic level. Trying to understand the essence of all things, they recorded in great detail laboratory techniques, equipment and information about chemical glassware, with great scrupulousness and diligence in passing on their experience to colleagues and descendants.
Need for classification
By the 19th century, sufficient information about a wide variety of chemical elements had been accumulated, which gave rise to the natural need and desire of scientists to systematize them. But to carry out such a classification, additional experimental data was required, as well as not mystical, but real knowledge about the structure of substances and the essence of the basis of the structure of matter, which did not yet exist. In addition, the available information about the meaning of the atomic masses of the chemical elements known at that time, on the basis of which the systematization was carried out, was not particularly accurate.
But attempts at classification among natural scientists were repeatedly made long before the understanding of the true essence of things, which now forms the basis of modern science. And many scientists worked in this direction. In briefly describing the prerequisites for the discovery of Mendeleev's periodic law, it is worth mentioning examples of such combinations of elements.
Triads
Scientists of those times felt that the properties exhibited by a wide variety of substances were undoubtedly dependent on the magnitude of their atomic masses. Realizing this, the German chemist Johann Döbereiner proposed his own system of classification of the elements that form the basis of matter. This happened in 1829. And this event was quite a serious advance in science for that period of its development, as well as an important stage in the history of the discovery of the periodic law. Döbereiner united known elements into communities, giving them the name "triad". According to the existing system, the mass of the outer elements turned out to be equal to the average of the sum of the atomic masses of the member of the group that was between them.
Attempts to expand the boundaries of triads
There were enough shortcomings in the mentioned Döbereiner system. For example, in the chain of barium, strontium, and calcium there was no magnesium, similar in structure and properties. And in the community of tellurium, selenium, and sulfur there was not enough oxygen. Many other similar substances also could not be classified according to the triad system.
Many other chemists tried to develop these ideas. In particular, the German scientist Leopold Gmelin sought to expand the “tight” framework, expanding the groups of classified elements, distributing them in order of equivalent weights and electronegativity of the elements. Its structures formed not only triads, but also tetrads and pentads, but the German chemist never managed to grasp the essence of the periodic law.
Spiral de Chancourtois
An even more complex scheme for constructing elements was invented by Alexandre de Chancourtois. He placed them on a plane rolled into a cylinder, distributing them vertically with an inclination of 45° in order of increasing atomic masses. As expected, substances with similar properties should have been located along lines parallel to the axis of a given volumetric geometric figure.
But in reality, an ideal classification did not work out, since sometimes completely unrelated elements fell into one vertical. For example, next to the alkali metals, manganese turned out to have a completely different chemical behavior. And the same “company” included sulfur, oxygen and the element titanium, which is not at all similar to them. However, a similar scheme also made its contribution, taking its place in the history of the discovery of the periodic law.
Other attempts to create classifications
Following those described, John Newlands proposed his own classification system, noting that every eighth member of the resulting series exhibits similarity in the properties of elements arranged in accordance with the increase in atomic mass. It occurred to the scientist to compare the discovered pattern with the structure of the arrangement of musical octaves. At the same time, he assigned each of the elements its own serial number, arranging them in horizontal rows. But such a scheme again did not turn out to be ideal and was assessed very skeptically in scientific circles.
From 1964 to 1970 tables organizing chemical elements were also created by Odling and Meyer. But such attempts again had their drawbacks. All this happened on the eve of Mendeleev’s discovery of the periodic law. And some works with imperfect attempts at classification were published even after the table that we use to this day was presented to the world.
Biography of Mendeleev
The brilliant Russian scientist was born in the city of Tobolsk in 1834 in the family of a gymnasium director. In addition to him, there were sixteen other brothers and sisters in the house. Not deprived of attention, as the youngest of the children, Dmitry Ivanovich from a very young age amazed everyone with his extraordinary abilities. His parents, despite the difficulties, strove to give him the best education. Thus, Mendeleev first graduated from a gymnasium in Tobolsk, and then from the Pedagogical Institute in the capital, while maintaining a deep interest in science in his soul. And not only to chemistry, but also to physics, meteorology, geology, technology, instrument making, aeronautics and others.
Soon Mendeleev defended his dissertation and became an associate professor at St. Petersburg University, where he lectured on organic chemistry. In 1865, he presented his doctoral dissertation to his colleagues on the topic “On the combination of alcohol with water.” The year the periodic law was discovered was 1969. But this achievement was preceded by 14 years of hard work.
About the great discovery
Taking into account errors, inaccuracies, as well as the positive experience of his colleagues, Dmitry Ivanovich was able to systematize chemical elements in the most convenient way. He also noticed the periodic dependence of the properties of compounds and simple substances, their shape on the value of atomic masses, which is stated in the formulation of the periodic law given by Mendeleev.
But such progressive ideas, unfortunately, did not immediately find a response in the hearts of even Russian scientists, who accepted this innovation very warily. And among figures of foreign science, especially in England and Germany, Mendeleev’s law found its most ardent opponents. But very soon the situation changed. What was the reason? The brilliant courage of the great Russian scientist some time later appeared to the world as evidence of his brilliant ability of scientific foresight.
New elements in chemistry
The discovery of the periodic law and the structure of the periodic table created by him made it possible not only to systematize substances, but also to make a number of predictions about the presence in nature of many elements unknown at that time. That is why Mendeleev managed to put into practice what other scientists had not been able to do before him.
Only five years passed, and the guesses began to be confirmed. The Frenchman Lecoq de Boisbaudran discovered a new metal, which he named gallium. Its properties turned out to be very similar to eka-aluminum predicted by Mendeleev in theory. Having learned about this, representatives of the scientific world of those times were stunned. But the amazing facts didn’t end there. Then the Swede Nilsson discovered scandium, the hypothetical analogue of which turned out to be ekabor. And the twin of eca-silicon was germanium, discovered by Winkler. Since then, Mendeleev's law began to take hold and gain more and more new supporters.
New facts of brilliant foresight
The creator was so carried away by the beauty of his idea that he took it upon himself to make some assumptions, the validity of which was later most brilliantly confirmed by practical scientific discoveries. For example, Mendeleev arranged some substances in his table not at all in accordance with increasing atomic masses. He foresaw that periodicity in a deeper sense is observed not only in connection with the increase in the atomic weight of elements, but also for another reason. The great scientist guessed that the mass of an element depends on the amount of some more elementary particles in its structure.
Thus, the periodic law in some way prompted representatives of science to think about the components of the atom. And scientists of the soon to come 20th century - the century of grandiose discoveries - were repeatedly convinced that the properties of elements depend on the magnitude of the charges of atomic nuclei and the structure of its electronic shell.
Periodic law and modernity
The periodic table, while remaining unchanged in its core, was subsequently supplemented and altered many times. It formed the so-called zero group of elements, which includes inert gases. The problem of placement of rare earth elements was also successfully solved. But despite the additions, the significance of the discovery of Mendeleev’s periodic law in its original version is quite difficult to overestimate.
Later, with the phenomenon of radioactivity, the reasons for the success of such systematization, as well as the periodicity of the properties of the elements of various substances, were fully understood. Soon, isotopes of radioactive elements also found their place in this table. The basis for the classification of numerous cell members was the atomic number. And in the middle of the 20th century, the sequence of arrangement of elements in the table was finally justified, depending on the filling of the orbitals of atoms with electrons moving at enormous speed around the nucleus.
Loading...