How to make chemical formulas based on valency. Video lesson “Valence of chemical elements. Determination of valency using formulas of compounds. Drawing up formulas for valence. Drawing up chemical formulas by valency

Lesson type. Combined.

Teaching methods. Partially searchable.

Goals. Didactic: consolidate the concept of “valency”, skills in determining valency using the formula and the Periodic Table.

Psychological: arouse interest in the subject, develop the ability to reason logically, and correctly express one’s thoughts.

Educational: develop the ability to work collectively, evaluate the answers of your comrades.

Equipment. Kits for building models of molecules of various substances, anagram tablets for chemical warm-up, efficiency target

1. Indicative-motivational stage

Chemical warm-up

Anagrams are words in which the order of the letters has been changed. Try to solve some of the chemical anagrams. Rearrange the letters in each word and get the name of the chemical element. Pay attention to the hint.

“Odovrod” – this element has the smallest relative atomic mass.

“Mailinu” – this element is called “winged” metal.

“Dikosolr” is part of the air.

“Tsalkiy” - without it our bones would be weak and fragile.

“Ozegel” - this element is part of the blood and is involved in the transfer of oxygen.

Teacher. If you can easily guess the anagram words, tell yourself: “I’m great!”

2. Updating knowledge

Catch a mistake (Guys look for a mistake, work in pairs, argue, confer. Having come to an opinion, they offer their own reasoned answer)

The word “valency” (from the Latin “valentia”) arose in the middle of the 19th century, during the period of completion of the chemical-analytical stage of the development of chemistry. “Valency is the ability of atoms of one element to attach a certain number of atoms of another element.” One atom of another monovalent element (HF, NaCl) is combined with one atom of a monovalent element. Combine with an atom of a divalent element one atom of monovalent (H 2 O) or one divalent atom (CaO). This means that the valence of an element can be represented as a number that shows how many atoms of a monovalent element an atom of a given element can combine with.

There are elements that have constant valence:
monovalent (I) - H, Li, Na, Rb, Cs, F, I
divalent (II) - Be, Mg, Ca, Sr, Ba, Zn, Cd K
trivalent (III) - B, Al, O

Tic Tac Toe: (Connect the elements with a straight line, the criterion for the correct answer is the constant valence of the selected elements)

1 option

Option 2

3. Learning new knowledge

Task 1: the general formula for combining hydrogen with any element is given

Knowing that the valency of hydrogen is I, determine the valence of the element.

The guys work in pairs, if necessary, they unite in groups of four, argue, and confer. Having come to an opinion, they offer their own reasoned answer. As a result, we get scheme No. 1

scheme 1

Task for consolidation:

1. determine the valences of elements in compounds with hydrogen: PH 3, HF, H 2 S, CaH 2,
2. name the connections.

Task 2: in the same way, you can determine the valence of elements in compounds with oxygen, knowing that oxygen is divalent. For example:

The guys work in pairs, if necessary, they unite in groups of four, argue, and confer. Having come to an opinion, they offer their own reasoned answer. As a result, we get scheme No. 2

scheme 2

Task for consolidation:

1. Determine the valences of elements in compounds with oxygen:

NO 2, N 2 O 5, SO 2, SO 3, Cl 2 O 7.

2. What are binary compounds containing oxygen called?

Task 3: what do you need to know in order to determine the valence of elements in a binary compound? (valence of one of the elements)

Determine the valence of atoms in a compound

The guys work in pairs, if necessary, they unite in groups of four, argue, and confer. Having come to an opinion, they offer their own reasoned answer. As a result, we get scheme No. 3

Teacher: which of the following diagrams

scheme 2

most fully reflects the rule for determining valency using the formula? (Scheme 3, because it reflects the general case, and Schemes 1 and 2 are only particular)

4. Consolidation of the studied material.

Independent work

The text of the work is written in advance on the board. Two students solve the problem on the back of the board, the rest in their notebooks.

Task 4. Check whether the formulas of the following compounds are written correctly: Na 2 S, KBr, Al 2 O 3, Mg 3 N 2, MgO.

5. Generalization and systematization of knowledge.

Creative work in groups

Task 5. Using kits for making models of molecules of various substances, create formulas and models of molecules for the following compounds:

1st group – copper and oxygen,

2nd group – zinc and chlorine,

3rd group – potassium and iodine,

4th group – magnesium and sulfur.

After finishing the work, one student from the group reports on the completed task and, together with the class, analyzes the errors.

Task 6. Write the formulas for compounds of metals with non-metals: calcium with oxygen, aluminum with chlorine, sodium with phosphorus. Name these connections.

After completing the work, students exchange notebooks and mutual checking takes place.

Task 7. Write down the procedure for drawing up formulas of substances, analyzing the proposed example

6. Reflection

You have the opportunity to self-assess your activities in class. You are presented with an “Efficiency Target”.

Mark your knowledge on a new topic by marking the corresponding sector in the picture with shading. Submit your notes.

7. Homework. According to the textbook “Chemistry-8” (UMK Kuznetsova N.E. and others) § 14, exercise 1-71 is mandatory (additional from 1-72 to 1-74).

Reports about the French scientist J.L. Proust and the English scientist J. Dalton.

Literature

1. Kuznetsova N.E. and others. Chemistry: Textbook for 8th grade students of general education institutions. - M.: Ventana-Graf, 2010. - 320 pp.: ill.
2. Kuznetsova N.E., Shatalov M.A. Teaching chemistry based on interdisciplinary integration: grades 8-9: Educational manual. - M.: Ventana-Graf, 2004. - 352 p.
3. Emelyanova E.O., Iodko A.G. Organization of cognitive activity of students in chemistry lessons in grades 8-9. Basic notes with practical tasks, tests: In 2 parts. Part I. – M.: School press, 2002.- 144 p.
4. Kuznetsova L.M. New technology for teaching chemistry in grade 8. - Obninsk: Title, 1999. - 208 p.: ill.

Lesson in 8th grade

Subject: " Drawing up chemical formulas by valency."

Goals:

consolidate the ability to determine valency using the formulas of compounds;

introduce the concept of “binary compounds”;

teach how to make names of binary compounds using their formulas;

teach how to compose formulas for compounds based on the valency of elements.

(You will learn :

what substances are called binary;

how to correctly formulate the name of a binary compound;

how valence is used to clarify the names of substances;

how to make up their formulas based on the names of binary compounds.

Remember :

what is valence;

how to determine valency, knowing the formula of a substance.)

During the classes.

Organizing time. Checking homework.

What is the valence of chemical elements?

Why is the valence of hydrogen taken as unity?

Which chemical elements have constant valence?

What chemical elements have variable valency?

New topic.

In the last lesson we learned how to determine the valency of chemical elements using the formulas of substances. Determine the valency of the elements in these compounds.

(independently, then check with the whole class)

Na 2 O SO 3 Fe 2 O 3 Ag 2 OCaH 2 H 2 S

In all these compounds we knew the valence of one element. What if there is no chemical element with a known valence? PSHE will come to the rescue (8 groups, metals and non-metals).

Rules for determining valence:

The valence of metals in group A is equal to the group number.

Nonmetals exhibit two valences: the maximum, equal to the group number, and the minimum, equal to 8 - the group number.

Let's look again at the series of connections written on the board. What do these connections have in common?

(complex substances; consist of two chemical elements)

Compounds formed by atoms of two chemical elements are calledbinary . Give another example of a binary compound that you encounter every day (water ).

Now we will learn how to give names to binary compounds. In chemistry, special rules have been developed for naming substances and drawing up formulas, which are called nomenclature. Only for a small number of substances are the so-called trivial names (i.e., historically established) retained. We will become familiar with the rules of chemical nomenclature gradually as we become familiar with the classification of substances.

Compilation of names of binary compounds (Appendix 1):

We name the chemical element whose sign in the formula is in second place. We use its Latin name. Select the root and add the suffix – id.

Presentation, slide 2.

Give names to the substances shown on the board.(Together).

Let's create the nomenclature names for carbon dioxide and carbon monoxide:

carbon dioxide - CO 2 – carbon monoxide;

carbon monoxide – CO – carbon monoxide.

It turned out that different substances have the same names. But this cannot happen. What do we do?

Valence will help here. Determine the valence of carbon in these compounds. Write down: carbon monoxide (IV), carbon monoxide (II).

Knowing the valence of elements, we can create formulas for substances. Let's create the formula for nitric oxide (V). To do this, you need to perform the following steps (Appendix 2, presentation, slide 3):

Find NOC.

Divide the NOC by the valency of the elements.

Presentation, slide 4.

Using the algorithm, create the formula for aluminum oxide.

Lesson summary.

Determine the valence of chromium atoms in the compounds:

CrO 3

CrO

Cr 2 O 3

Give them names.

Check: presentation, slide 6.

Homework.

§12, questions 4-7 p. 37 (written), task 2 p. 37.

Appendix 1. Compilation of names of binary compounds:

We name the chemical element whose sign in the formula is in second place. We use its Latin name. Select the root and add the suffix –id to it.

We name the chemical element whose sign comes first in the formula of the substance. We use the Russian name in the genitive case.

CaO – ok eid calcium

NaCl – chlorine eid sodium

PbS – sulf eid lead

Chemical element sign

Latin name

Russian name

Sa

calcium

ok igenium

oxygen

sodium

chlorine mind

chlorine

lead

sulf ur

sulfur

Appendix 2. Drawing up chemical formulas of binary compounds by their names.

Nitric oxide ( V )

Write down the signs of chemical elements.N O

V II

Indicate the valence of elements.N O

10

Find NOC.

Divide the NOC by the valency of the elements. [N] 10: V=2 [O] 10: II= 5

Place indexes (bottom right).N 2 O 5

C leaving binary formulas

by valences of chemical elements

One chemical element attaches or replaces a certain number of atoms of another.

The unit of valence is taken to be the valency of a hydrogen atom equal to 1, that is, hydrogen is monovalent. Therefore, the valency of an element indicates how many hydrogen atoms one atom of the element in question is connected to. For example, HCl, where chlorine is monovalent; H2O, where oxygen is divalent; NH 3, where nitrogen is trivalent.

Table of elements with constant valency.

Formulas of substances can be compiled according to the valences of their constituent elements. And vice versa, knowing the valences of elements, you can compose a chemical formula from them.

Algorithm for compiling formulas of substances by valence.

1. Write down the symbols of the elements.

2. Determine the valency of the elements included in the formula.

3. Find the least common multiple of the numerical values ​​of valency.

4. Find the relationships between the atoms of the elements by dividing the found least common multiple by the corresponding valences of the elements.

5. Write down the indices of the elements in the chemical formula.

Example: Let's create the chemical formula of phosphorus oxide.

1. Write down the symbols:

2. Let's determine valencies:

4. Let's find the relationships between atoms:

5. Write down the indices:

Algorithm for determining valency using the formulas of chemical elements.

1. Write down the formula of a chemical compound.

2. Designate the known valence of elements.

3. Find the least common multiple of valence and index.

4. Find the ratio of the least common multiple to the number of atoms of the second element. This is the desired valence.

5. Check by multiplying the valence and index of each element. Their products must be equal.

Example: Let's determine the valence of hydrogen sulfide elements.

1. Let's write the formula:

H 2 S

2. Let us denote the known valence:

H 2 S

3. Find the least common multiple:

H 2 S

4. Find the ratio of the least common multiple to the number of sulfur atoms:

H 2 S

5. Let's do a check.

Lesson topic: Valence. Drawing up formulas for valence.

The purpose of the lesson: contribute to the formation in students of the concept of “valency” and the ability to determine the valence of atoms of elements using the formulas of substances

Planned learning outcomes:

1. Students should be able to formulate the definition of “valency”, know the valence of hydrogen and oxygen atoms in compounds, and use it to determine the valence of atoms of other elements in binary compounds,
2. Be able to explain the meaning of the concept of “valence” and the sequence of actions when determining the valence of atoms of elements using the formulas of substances.

Concepts introduced for the first time in class: valence.

Equipment: ball-and-stick models of atoms, plastic boxes with sand, instructional cards for students, computer, projector.

During the classes

I. Organizational moment. (2 min.)

Hello guys! I'm very glad to see you! Those who can name one external sign of a chemical reaction can sit down!

II.Checking homework.(6 min.)

Most recently, you and I studied the symbols of chemical elements, learned to write formulas, and now I propose to test your knowledge in the game “Chemical Shooting Range”, for this we will divide into two teams: Sasha and Nikita will go to the monitor, they will be “technical performers”, I remind you of the rules game - five targets pop up in front of you, but only one has the correct image, it is this target that you must shoot at! (Game "Chemical Range") Close your eyes sharply and open them!

III.Communication of the topic and purpose of the lesson. (2 min.)

The topic of our lesson is “Valence. Drawing up formulas based on valency." Let's try to formulate the purpose of our lesson! Write down the date and topic of the lesson in your notebook.

IV.Explanation of new material. (20 minutes.)

– Until now, we have used ready-made formulas given in the textbook. Chemical formulas can be derived based on data on the composition of substances. But most often, when drawing up chemical formulas, the patterns that the elements obey when connecting with each other are taken into account.

Exercise: Help me, with the help of your cards, write down the formulas of the compounds of hydrogen and chlorine, hydrogen and oxygen, nitrogen and hydrogen, carbon and hydrogen. Compare the qualitative and quantitative composition in molecules: HCl, H 2 O, NH 3, CH 4.

Conversation with students:

– What do the molecules have in common?

Suggested answer:Presence of hydrogen atoms.

We will answer later how they differ from each other! Now I offer you an unusual fragment of the lesson, it is called “Send Play”, this is an English word, maybe someone can translate it? (Playing with sand).

Go to the table, there is a surprise hidden in these drawers, but before we get to it, let's “slide” our palms along the surface of the sand, performing zigzag and circular movements, perform the same movements, placing our palm on the edge, “walk” our palms along the laid paths , leaving your marks on them, play on the surface of the sand, like on a piano or computer keyboard. Now, plunge your hands into the sand and feel for the “surprise”, without taking anything out, try to guess: What is it? Wipe your hands with wet wipes and assemble the HCl, H models 2 O, NH 3, CH 4. We work in pairs.

I suggest returning to the question, what is the difference?composition of these molecules?

Suggested answer:

• HCl – one chlorine atom holds one hydrogen atom,
• H 2 O – one oxygen atom holds two hydrogen atoms,
• NH 3 – one nitrogen atom holds three hydrogen atoms,
• CH 4 – one carbon atom holds four hydrogen atoms.

The problem arises: Why do different atoms hold different numbers of hydrogen atoms?(We listen to the students' answers.)

Conclusion: Atoms have different abilities to hold a certain number of other atoms in compounds. This is called valence. (Attach a card with the term to the board) The word “valence” comes from the Latin. valentia – strength. Pay attention to the spelling of this word, they are underlined! You will need to write down the new term in the dictionary. Open your textbook to page 32, find the definition, read it aloud.

Valence is indicated by Roman numerals.

The valency of the hydrogen atom is taken to be one, and that of oxygen is II.

I am giving you an algorithm for determining valence and we are trying to put it into practice:(teacher works at the blackboard)

Valency determination algorithm.

V. Fastening (4 min.)

Within four minutes you must complete one of three tasks of your choice. Choose only the task that you can handle. The task is in the handout.

• Determine the valence of atoms of chemical elements using the formulas of compounds: NH 3, Au 2 O 3, SiH 4, CuO.
• Application layer (“4”).From the given series, write down only those formulas in which the metal atoms are divalent: MnO, Fe 2 O 3, CrO 3, CuO, K 2 O, CaH 2.
• Creative level (“5”).Find a pattern in the sequence of formulas: N 2 O, NO, N 2 O 3

Work on mistakes.Answers are on the back of the board.

VI. Summing up the lesson. (5 min.)

Our lesson is coming to an end, at You have the opportunity to self-assess your activities in class. You are presented with an “Efficiency Target”.

Mark your knowledge on the new topic by marking the corresponding sector in the picture with the letter of your name.

Conversation with students, in the next lesson we will continue to study this topic and compare the results of the “Performance Target”

• What problem did we pose at the beginning of the lesson?
• What conclusion have we reached?
• Define “valence”.
• What is the valency of a hydrogen atom? Oxygen?
• Have you achieved the goal of the lesson?

Assessing the work of students as a whole and individual students.

VII. Homework: (1 min.)§ 11-12, pp. 32–34, exercise 4 on p. 37.

Preview:

Sand-play.

Playing in the sand is one of the natural activities of a child.
The principle of “sand therapy” was proposed by Carl Gustav Jung, a wonderful psychotherapist and founder of analytical therapy. Perhaps the natural human need to tinker with sand, and its very structure, suggested this idea to the great Jung. The formation of the concept of “sand therapy” (or “sand-play”) was mainly carried out by representatives of the Jungian school.

Regardless of age, sand therapy helps:
- develop cognitive processes (perception, attention, memory, figurative and logical thinking, spatial imagination), self-regulation processes;
- develop the sensory-perceptual sphere, creativity, and form communication skills;
- train fine motor skills of hands;
- harmonize the psycho-emotional state;
- develop a positive attitude towards yourself.

Educational games on the sand.
1. Getting to know the world around you.
Wild and domestic animals, insects, forests, fields, rivers, lakes, seas, islands, professions, cities, transport, everyday life.
2. Geography games.
We simulate various climatic zones and life in them in the sandbox.
3. Fantastic games.
The sandbox simulates life on other planets: the lunar landscape, the surface of Mars.
4. Historical games.
Only in a sandbox can a child build everything himself and lose, becoming a participant in historical events.
5. Games-excursions around the city.
The homeland begins with the hometown, village. Its history has a significant impact on the way residents think and live. The history of the city, like the life path of a person, has its joys and sorrows. These events can be played out on the sand.

Preview:

Preview:

Vality

N 2 O, NO, N 2 O 3 and assign valences to each element.

Reproductive level (“3”).

Application layer (“4”).

Creative level (“5”).

N 2 O, NO, N 2 O 3 and assign valences to each element.

Reproductive level (“3”).Determine the valence of atoms of chemical elements using the formulas of compounds:

NH 3, Au 2 O 3, SiH 4, CuO.

Application layer (“4”).From the given series, write down only those formulas in which the metal atoms are divalent:

MnO, Fe 2 O 3, CrO 3, CuO, K 2 O, CaH 2.

Creative level (“5”).Find a pattern in the sequence of formulas:

N 2 O, NO, N 2 O 3 and assign valences to each element.

Reproductive level (“3”).Determine the valence of atoms of chemical elements using the formulas of compounds:

NH 3, Au 2 O 3, SiH 4, CuO.

Application layer (“4”).From the given series, write down only those formulas in which the metal atoms are divalent:

MnO, Fe 2 O 3, CrO 3, CuO, K 2 O, CaH 2.

Creative level (“5”).Find a pattern in the sequence of formulas:

N 2 O, NO, N 2 O 3 and assign valences to each element.

Reproductive level (“3”).Determine the valence of atoms of chemical elements using the formulas of compounds:

NH 3, Au 2 O 3, SiH 4, CuO.

Application layer (“4”).From the given series, write down only those formulas in which the metal atoms are divalent:

MnO, Fe 2 O 3, CrO 3, CuO, K 2 O, CaH 2.

Creative level (“5”).Find a pattern in the sequence of formulas:

N 2 O, NO, N 2 O 3 and assign valences to each element.

Reproductive level (“3”).Determine the valence of atoms of chemical elements using the formulas of compounds:

NH 3, Au 2 O 3, SiH 4, CuO.

Application layer (“4”).From the given series, write down only those formulas in which the metal atoms are divalent:

MnO, Fe 2 O 3, CrO 3, CuO, K 2 O, CaH 2.

Creative level (“5”).Find a pattern in the sequence of formulas:

N 2 O, NO, N 2 O 3 and assign valences to each element.