Chemical formula h2. H2O2 - what is this substance? IV Distributing shared electrons

The formulas for covalent bonds are fundamentally different from the formulas for ionic bonds. The fact is that covalent compounds can be formed in a variety of ways, so different compounds may appear as a result of the reaction.

1. Empirical formula

The empirical formula specifies the elements that make up the molecule in their smallest whole number ratios.

For example, C 2 H 6 O - the compound contains two carbon atoms, six hydrogen atoms and one oxygen atom.

2. Molecular formula

The molecular formula indicates which atoms the compound consists of and in what quantities these atoms are present in it.

For example, for the compound C 2 H 6 O, the molecular formulas can be: C 4 H 12 O 2; C6H18O3...

For full description covalent compound molecular formula is not enough:

As you can see, both compounds have the same molecular formula - C 2 H 6 O, but are completely different substances:

• dimethyl ether is used in refrigeration units;
• ethyl alcohol is the basis of alcoholic beverages.

3. Structural formula

The structural formula serves to precise definition covalent compound, because, in addition to the elements in the compound and the number of atoms, it also shows connection diagram connections.

The structural formula is used electron-dot formula And Lewis formula.

4. Structural formula for water (H 2 O)

Let's consider the procedure for constructing a structural formula using the example of a water molecule.

I Building the connection frame

The atoms of a compound are arranged around a central atom. The central atoms are usually: carbon, silicon, nitrogen, phosphorus, oxygen, sulfur.

II Find the sum of valence electrons of all atoms of the compound

For water: H 2 O = (2 1 + 6) = 8

A hydrogen atom has one valence electron, and an oxygen atom has 6. Since there are two hydrogen atoms in the compound, then total number The valence electrons of a water molecule will be equal to 8.

III Determine the number of covalent bonds in a water molecule

Determined by the formula: S = N - A, Where

S- the number of electrons shared in the molecule;

N- the sum of valence electrons corresponding to the completed external energy level of the atoms in the compound:

N=2- for the hydrogen atom;

N=8- for atoms of other elements

A- the sum of the valence electrons of all atoms in the compound.

N = 2 2 + 8 = 12

A = 2 1 +6 = 8

S = 12 - 8 = 4

There are 4 shared electrons in a water molecule. Since a covalent bond consists of a pair of electrons, we get two covalent bonds.

IV Distributing shared electrons

There must be at least one bond between the central atom and the atoms that surround it. For a water molecule there will be two such bonds for each hydrogen atom:

V Distribute the remaining electrons

Of the eight valence electrons, four have already been distributed. Where to “put” the remaining four electrons?

Each atom in the compound must have a full octet of electrons. For hydrogen it is two electrons; for oxygen - 8.

The shared electrons are called connecting.

The electron-dot formula and the Lewis formula clearly describe the structure covalent bond, but are bulky and take up a lot of space. These disadvantages can be avoided by using condensed structural formula, which indicates only the order of the connections.

An example of a condensed structural formula:

• dimethyl ether - CH 3 OCH 3
• ethyl alcohol - C 2 H 5 OH

The formula for the basis of life - water - is well known. Its molecule consists of two hydrogen atoms and one oxygen, which is written as H2O. If there is twice as much oxygen, then a completely different substance will be obtained - H2O2. What is it and how will the resulting substance differ from its “relative” water?

H2O2 - what is this substance?

Let's look at it in more detail. H2O2 is the formula of hydrogen peroxide, Yes, the same one that is used to treat scratches, white. Hydrogen peroxide H2O2 - scientific.

For disinfection, use a three percent peroxide solution. In pure or concentrated form, it causes chemical burns to the skin. A thirty percent peroxide solution is otherwise called perhydrol; Previously, it was used in hairdressers to bleach hair. The skin burned by it also turns white.

Chemical properties of H2O2

Hydrogen peroxide is a colorless liquid with a “metallic” taste. It is a good solvent and easily dissolves in water, ether, and alcohols.

Three and six percent peroxide solutions are usually prepared by diluting a thirty percent solution. When storing concentrated H2O2, the substance decomposes with the release of oxygen, so it should not be stored in tightly sealed containers to avoid an explosion. As the peroxide concentration decreases, its stability increases. You can also add H2O2 to it to slow down the decomposition various substances, for example, phosphoric or salicylic acid. To store solutions of high concentration (more than 90 percent), sodium pyrophosphate is added to peroxide, which stabilizes the state of the substance, and aluminum vessels are also used.

H2O2 can be both an oxidizing agent and a reducing agent in chemical reactions. However, more often peroxide exhibits oxidizing properties. Peroxide is considered to be an acid, but a very weak one; salts of hydrogen peroxide are called peroxides.

as a method of producing oxygen

The decomposition reaction of H2O2 occurs when the substance is exposed to high temperature (more than 150 degrees Celsius). As a result, water and oxygen are formed.

Reaction formula - 2 H2O2 + t -> 2 H2O + O2

The oxidation state of H in H 2 O 2 and H 2 O = +1.
Oxidation state of O: in H 2 O 2 = -1, in H 2 O = -2, in O 2 = 0
2 O -1 - 2e -> O2 0

O -1 + e -> O -2
2 H2O2 = 2 H2O + O2

The decomposition of hydrogen peroxide can also occur at room temperature if a catalyst is used ( Chemical substance, accelerating the reaction).

In laboratories, one of the methods for obtaining oxygen, along with decomposition bertholet salt or potassium permanganate, is the decomposition reaction of peroxide. In this case, manganese (IV) oxide is used as a catalyst. Other substances that accelerate the decomposition of H2O2 are copper, platinum, and sodium hydroxide.

History of the discovery of peroxide

The first steps towards the discovery of peroxide were taken in 1790 by the German Alexander Humboldt, when he discovered the transformation of barium oxide into peroxide when heated. That process was accompanied by the absorption of oxygen from the air. Twelve years later, scientists Tenard and Gay-Lussac conducted an experiment on burning alkali metals with excess oxygen, resulting in sodium peroxide. But hydrogen peroxide was obtained later, only in 1818, when Louis Thénard studied the effect of acids on metals; a low amount of oxygen was necessary for their stable interaction. Conducting a confirmatory experiment with barium peroxide and sulfuric acid, the scientist added water, hydrogen chloride and ice to them. After a short time, Tenar discovered small frozen drops on the walls of the container with barium peroxide. It became clear that this was H2O2. Then they gave the resulting H2O2 the name “oxidized water.” This was hydrogen peroxide - a colorless, odorless, difficult-to-evaporate liquid that dissolves other substances well. The result of the interaction of H2O2 and H2O2 is a dissociation reaction, peroxide is soluble in water.

An interesting fact is that the properties of the new substance were quickly discovered, allowing it to be used in restoration work. Tenar himself, using peroxide, restored a painting by Raphael that had darkened with time.

Hydrogen peroxide in the 20th century

After careful study of the resulting substance, it began to be produced on an industrial scale. At the beginning of the twentieth century, electrochemical technology for the production of peroxide, based on the process of electrolysis, was introduced. But the shelf life of the substance obtained by this method was short, about a couple of weeks. Pure peroxide is unstable, and for the most part it was produced in thirty percent concentration for bleaching fabrics and in three or six percent concentration for household needs.

Scientists fascist Germany used peroxide to create a liquid-fuel rocket engine that was used for defense purposes in World War II. As a result of the interaction of H2O2 and methanol/hydrazine, powerful fuel was obtained, on which the aircraft reached speeds of more than 950 km/h.

Where is H2O2 used now?

• in medicine - for treating wounds;
• in the pulp and paper industry the bleaching properties of the substance are used;
• in the textile industry, natural and synthetic fabrics, furs, and wool are bleached with peroxide;
• as rocket fuel or its oxidizer;
• in chemistry - to produce oxygen, as a foaming agent for the production of porous materials, as a catalyst or hydrogenating agent;
• for the production of disinfectants or cleaning agents, bleaches;
• for bleaching hair (this is an outdated method, since hair is severely damaged by peroxide);

Hydrogen peroxide can be successfully used to solve various household problems. But only three percent hydrogen peroxide can be used for these purposes. Here are some ways:

• To clean surfaces, you need to pour peroxide into a container with a spray bottle and spray it on contaminated areas.
• To disinfect objects, they need to be wiped with an undiluted H2O2 solution. This will help cleanse them of harmful microorganisms. Washing sponges can be soaked in water with peroxide (1:1 ratio).
• To bleach fabrics, add a glass of peroxide when washing white items. You can also rinse white fabrics in water mixed with a glass of H2O2. This method restores whiteness, protects fabrics from yellowing and helps remove stubborn stains.
• To combat mold and mildew, mix peroxide and water in a 1:2 ratio in a container with a spray bottle. Spray the resulting mixture onto contaminated surfaces and after 10 minutes clean them with a brush or sponge.
• You can renew darkened grout in tiles by spraying peroxide on the desired areas. After 30 minutes, you need to thoroughly rub them with a stiff brush.
• To wash dishes, add half a glass of H2O2 to a full basin of water (or a sink with a closed drain). Cups and plates washed in this solution will shine clean.
• To clean your toothbrush, you need to dip it in an undiluted three percent peroxide solution. Then rinse under strong running water. This method disinfects hygiene items well.
• To disinfect purchased vegetables and fruits, you should spray a solution of 1 part peroxide and 1 part water on them, then rinse them thoroughly with water (can be cold).
• At your summer cottage, using H2O2 you can fight plant diseases. You need to spray them with a peroxide solution or soak the seeds shortly before planting in 4.5 liters of water mixed with 30 ml of forty percent hydrogen peroxide.
• To revive aquarium fish, if they are poisoned by ammonia, suffocated when the aeration is turned off, or for another reason, you can try placing them in water with hydrogen peroxide. You need to mix three percent peroxide with water at the rate of 30 ml per 100 liters and place lifeless fish in the resulting mixture for 15-20 minutes. If they do not come to life during this time, then the remedy did not help.

Even as a result of vigorously shaking a bottle of water, a certain amount of peroxide is formed in it, since the water is saturated with oxygen during this action.

Fresh fruits and vegetables also contain H2O2 until they are cooked. When heating, cooking, frying and other processes with accompanying high temperatures, a large amount of oxygen is destroyed. This is why cooked foods are considered not so healthy, although some vitamins remain in them. Freshly squeezed juices or oxygen cocktails served in sanatoriums are useful for the same reason - due to saturation with oxygen, which gives the body new strength and cleanses it.

Danger of peroxide when ingested

After the above, it may seem that peroxide can be specifically taken orally, and this will benefit the body. But this is not true at all. In water or juices, the compound is found in minimum quantities and is closely related to other substances. Taking “unnatural” hydrogen peroxide internally (and all peroxide purchased in a store or produced as a result of chemical experiments independently cannot be considered natural, and also has too high a concentration compared to natural) can lead to dangers to life and health consequences. To understand why, we need to turn again to chemistry.

As already mentioned, under certain conditions, hydrogen peroxide breaks down and releases oxygen, which is an active oxidizing agent. can occur when H2O2 collides with peroxidase, an intracellular enzyme. The use of peroxide for disinfection is based on its oxidizing properties. So, when a wound is treated with H2O2, the released oxygen destroys living pathogenic microorganisms that have entered it. It has the same effect on other living cells. If you treat intact skin with peroxide and then wipe the treated area with alcohol, you will feel a burning sensation, which confirms the presence of microscopic damage after peroxide. But when low concentration peroxide is used externally, there will be no noticeable harm to the body.

It’s another matter if you try to take it orally. That substance, which can damage even relatively thick skin on the outside, ends up on the mucous membranes of the digestive tract. That is, chemical mini-burns occur. Of course, the released oxidizing agent - oxygen - can also kill harmful microbes. But the same process will happen with the cells of the food tract. If burns as a result of the action of the oxidizing agent are repeated, then atrophy of the mucous membranes is possible, and this is the first step on the path to cancer. The death of intestinal cells leads to the body's inability to absorb nutrients, which explains, for example, weight loss and the disappearance of constipation in some people who practice “treatment” with peroxide.

Separately, it is necessary to say about this method of using peroxide, such as intravenous injections. Even if for some reason they were prescribed by a doctor (this can only be justified in case of blood poisoning, when there are no other suitable drugs available), then under medical supervision and with strict dosage calculations, there are still risks. But in such extreme situation this will be a chance for recovery. Under no circumstances should you prescribe hydrogen peroxide injections to yourself. H2O2 poses a great danger to blood cells - red blood cells and platelets, since it destroys them when it enters the bloodstream. In addition, a fatal blockage of blood vessels by the released oxygen can occur - a gas embolism.

Safety precautions for handling H2O2

• Keep out of the reach of children and disabled persons. The lack of odor and distinct taste makes peroxide especially dangerous for them, since large doses can be taken. If the solution gets inside, the consequences of use can be unpredictable. You should consult a doctor immediately.
• Peroxide solutions with a concentration of more than three percent cause burns if they come into contact with the skin. The burn area should be washed with plenty of water.

• Do not allow the peroxide solution to get into your eyes, as this will cause swelling, redness, irritation, and sometimes pain. First aid before contacting a doctor is to wash the eyes generously with water.
• Store the substance in such a way that it is clear that it is H2O2, that is, in a container with a sticker to avoid accidental use for other purposes.
• Storage conditions that prolong its life are a dark, dry, cool place.
• Hydrogen peroxide should not be mixed with any liquids other than clean water, including chlorinated tap water.
• All of the above applies not only to H2O2, but also to all preparations containing it.

DEFINITION

Hydrogen(chemical symbol – H) – chemical element with atomic number 1 (the first element in periodic table). Located in the first period in the first (I) or seventh (VII) group of the periodic system.

Atomic mass: 1.008 amu

Electronic formula: 1s 1

The dual position of hydrogen in the periodic table is explained by the fact that it has a certain similarity with both alkali metals and halogens. Like alkali metal atoms, a hydrogen atom can give up its only electron (oxidize) and become positively charged and it is H +. Like halogen atoms, a hydrogen atom can add another electron to form a stable noble gas (helium) configuration, i.e. recover and turn into a negatively charged H – ion.

The electronegativity of hydrogen has an intermediate value (2.1) between the electronegativity values ​​of typical metals and typical nonmetals.

Hydrogen– a simple substance consisting of two hydrogen atoms.

Formula: H2.

Structural formula:

Under normal conditions, hydrogen is a colorless, tasteless, and odorless gas. The easiest of known substances. hydrogen is 0.08987 g/l under normal conditions.

In nature, hydrogen exists in the form of three isotopes that have individual names: 1 H - protium (H), 2 H - deuterium (D), 3 H - tritium (T). Protium and deuterium are stable isotopes, tritium is radioactive with a half-life of 12.32 years.

Natural hydrogen consists of H 2 and HD molecules in a ratio of 3200:1. The content of pure D 2 is even less.

Physical and Chemical properties The isotopes of hydrogen are quite different from each other, unlike the isotopes of other chemical elements. This is because the addition of each additional proton causes a large relative increase in the atom.

Hydrogen is basic integral part stars and interstellar gas. The share of hydrogen atoms in the Universe is 88.6%.

According to the reaction equation

In our case, therefore, aluminum is taken in excess; we make the calculation using hydrochloric acid.

Chemical formula is an image using symbols.

Chemical element signs

Chemical sign or chemical element symbol– this is the first or two first letters of the Latin name of this element.

For example: FerrumFe , Cuprum –Cu , OxygeniumO etc.

Table 1: Information provided by a chemical symbol

The name of a chemical symbol in most cases is read as the name of a chemical element. For example, K – potassium, Ca – calcium, Mg – magnesium, Mn – manganese.

Cases when the name of a chemical symbol is read differently are given in Table 2:

Chemical formulas of simple substances

The chemical formulas of most simple substances (all metals and many non-metals) are the signs of the corresponding chemical elements.

So iron substance And chemical element iron are designated the same - Fe .

If it has a molecular structure (exists in the form , then its formula is the chemical sign of the element with index bottom right indicating number of atoms in a molecule: H 2, O2, O 3, N 2, F 2, Cl2, BR 2, P 4, S 8.

Table 3: Information provided by a chemical sign

Chemical formulas of complex substances

The formula of a complex substance is prepared by writing down the signs of the chemical elements of which the substance is composed, indicating the number of atoms of each element in the molecule. In this case, as a rule, chemical elements are written in order of increasing electronegativity in accordance with the following practical series:

Me, Si, B, Te, H, P, As, I, Se, C, S, Br, Cl, N, O, F

For example, H2O , CaSO4 , Al2O3 , CS 2 , OF 2 , NaH.

The exceptions are:

• some compounds of nitrogen with hydrogen (for example, ammonia NH 3 , hydrazine N 2H 4 );
• salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
• hydrocarbons ( CH 4 , C2H4 , C2H2 ).

Chemical formulas of substances existing in the form dimers (NO 2 , P2O 3 , P2O5, salts of monovalent mercury, for example: HgCl , HgNO3 etc.), written in the form N 2 O4,P 4 O6,P 4 O 10Hg 2 Cl2,Hg 2 ( NO 3) 2 .

The number of atoms of a chemical element in a molecule and a complex ion is determined based on the concept valency or oxidation states and is recorded index lower right from the sign of each element (index 1 is omitted). In this case, they proceed from the rule:

the algebraic sum of the oxidation states of all atoms in a molecule must be equal to zero (the molecules are electrically neutral), and in a complex ion - the charge of the ion.

For example:

2Al 3 + +3SO 4 2- =Al 2 (SO 4) 3

The same rule is used when determining the oxidation state of a chemical element using the formula of a substance or complex. It is usually an element that has several oxidation states. The oxidation states of the remaining elements forming the molecule or ion must be known.

The charge of a complex ion is the algebraic sum of the oxidation states of all the atoms that form the ion. Therefore, when determining the oxidation state of a chemical element in a complex ion, the ion itself is placed in brackets, and its charge is taken out of brackets.

When compiling formulas for valence a substance is represented as a compound consisting of two particles of different types, the valencies of which are known. Next they use rule:

in a molecule, the product of valence by the number of particles of one type must be equal to the product of valence by the number of particles of another type.

For example:

The number before the formula in a reaction equation is called coefficient. She indicates either number of molecules, or number of moles of substance.

The coefficient before the chemical symbol, indicates number of atoms of a given chemical element, and in the case when the sign is the formula of a simple substance, the coefficient indicates either number of atoms, or the number of moles of this substance.

For example:

• 3 Fe– three iron atoms, 3 moles of iron atoms,
• 2 H– two hydrogen atoms, 2 moles of hydrogen atoms,
• H 2– one molecule of hydrogen, 1 mole of hydrogen.

The chemical formulas of many substances have been determined experimentally, which is why they are called "empirical".

Table 4: Information provided by the chemical formula of a complex substance

Graphic formulas

To obtain more complete information about a substance, use graphic formulas , which indicate order of connection of atoms in a molecule And valence of each element.

Graphic formulas of substances consisting of molecules sometimes, to one degree or another, reflect the structure (structure) of these molecules; in these cases they can be called structural .

To compile a graphical (structural) formula of a substance, you must:

• Determine the valence of all chemical elements that form the substance.
• Write down the signs of all chemical elements that form the substance, each in an amount equal to the number of atoms of a given element in the molecule.
• Connect the signs of chemical elements with dashes. Each dash denotes a pair that communicates between chemical elements and therefore belongs equally to both elements.
• The number of lines surrounding the sign of a chemical element must correspond to the valence of this chemical element.
• When formulating oxygen-containing acids and their salts, hydrogen atoms and metal atoms are bonded to the acid-forming element through an oxygen atom.
• Oxygen atoms are combined with each other only when formulating peroxides.

Examples of graphic formulas:

Check information. It is necessary to check the accuracy of the facts and reliability of the information presented in this article. On the talk page there is a discussion on the topic: Doubts regarding terminology. Chemical formula ... Wikipedia

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Books

• A brief dictionary of biochemical terms, Kunizhev S.M. , The dictionary is intended for students of chemical and biological specialties at universities studying general biochemistry, ecology and fundamentals of biotechnology, and can also be used in ... Category: Biology Publisher: VUZOVSKAYA KNIGA, Manufacturer: