The topic is drawing up formulas for valency. Drawing up chemical formulas by valency

Class 8 Lesson date

Lesson topic: Valence. Drawing up chemical formulas
by valence

Goals. Didactic: consider the concept of “valency” as the atomicity of an element, introduce students to different types of valency (higher and lower, variable and constant).

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.

Lesson type. Combined.

Teaching methods. Partially search, reproductive, programmed survey, conversation with elements of a lecture.

Epigraph for the lesson. “Every substance – from the simplest to the most complex – has three different but interconnected aspects: properties, composition, structure...” (B.M. Kedrov).

Equipment. Models of molecules of water, carbon dioxide, kits for constructing models of molecules of various substances, individual cards for checking homework and independent work of students in a group, anagram tablets for chemical warm-up, a scale for determining the emotional state of a student.

DURING THE CLASSES

Indicative-motivational stage

Psychological warm-up

The purpose of the warm-up is to determine the emotional state of students. Each student has a sign with six faces glued to the inside cover of their notebook - a scale for determining their emotional state (Fig.). Each student puts a tick under the face whose expression reflects his mood.

Rice. Determine your emotional state

Teacher. It would be great if by the end of the lesson everyone managed to move the check mark at least one box to the left.

To do this, you need to think about the questions: can a person fall in love with a subject that is not very interesting to him? What do I need to do?

Chemical warm-up

The warm-up is prepared and conducted by students.

Student. 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.

"Tjurt" - contained in a medical thermometer.

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

"Rosphof" - a substance consisting of atoms of this element, was smeared on the fur of the Baskerville dog.

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

Chemical symbols and chemical formulas
(Checking homework)

Individual work at the board using cards.

Card 1

(sample tasks for cards)

Exercise 1. Solve the riddle:

“I am both graphite and diamond,
In your body you have
Even though they burn me in the ovens -
They call it black gold!

Task 2. Answer the questions.

1. What chemical sign does this element have?

2. Is it a metal or non-metal?

3. What is its relative atomic mass?

4. Calculate the mass fraction of this element in the EO compound 2 .

Digital dictation

Students monitor the completion of the dictation using the method of mutual checking.

Exercise. Place the number 1 next to the correct statements, and 0 next to the incorrect ones.

1. A chemical element is a certain type of atom.

2. In each cell of D.I. Mendeleev’s table, in addition to the designation and name of the element, two numbers are written: the upper one is the relative atomic mass of the element, the lower one is its serial number.

3. The chemical element gallium was named after France.

4. In D.I. Mendeleev’s table, elements are arranged, as a rule, in descending order of their atomic masses.

5. Values ​​of relative atomic mass and atomic mass expressed in a. e.m., never coincide numerically.

6. Substances consisting of atoms of one element are called simple.

7. Index is a number showing the number of particles (atoms or molecules) of a substance taken.

8. The mass fraction of an element shows what part (share) the mass of a given element is of the total mass of the substance.

9. Relative molecular weight of water H 2 O is equal to 20.

10. The mass fraction of calcium in calcium oxide CaO is 71%.

CORRECT ANSWERS: 1 – 1, 2 – 0, 3 – 1, 4 – 0, 5 – 0, 6 – 1, 7 – 0, 8 – 1, 9 – 0, 10 – 1.

Operational and executive stage

Teacher. You know that chemical formulas of substances show the quantitative relationships in which atoms are connected to each other; you also learned how to calculate the mass fraction of an element using the chemical formula of a substance. For example, in water N 2 ABOUTFor one oxygen atom there are two hydrogen atoms, or 11% Nand 89% ABOUT.In carbon dioxide CO 2 There are two oxygen atoms for every carbon atom. (demonstration of models of molecules of these substances.)

Valence

Teacher. Valency is the ability of atoms to attach to themselves a certain number of other atoms.

One atom of another monovalent element is combined with one atom of a monovalent element (HF, NaCl). An atom of a divalent element combines with two atoms of a monovalent element. (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.

Rules for determining valence
elements in connections

The valency of hydrogen is taken to be I (one). Then, in accordance with the formula of water H 2 O to one oxygen atom there are two hydrogen atoms attached.

Oxygen in its compounds always exhibits valency II. Therefore, the carbon in the compound CO 2 (carbon dioxide) has a valence of IV.

Teacher. How to determine the valency of an element based on D.I. Mendeleev’s table?

For metals in groups a, the valency is equal to the group number.

Nonmetals generally exhibit two valences: higher and lower (scheme).

The highest valence is equal to the group number.

The lowest valence is equal to the difference between the number 8 (the number of groups in the table) and the number of the group in which the element is located.

Teacher. For example: sulfur has the highest valence VI and the lowest (8 – 6) equal to II; phosphorus exhibits valences V and III.

Valency can be constant (for elements of the main subgroups of D.I. Mendeleev’s table) or variable (for elements of side subgroups in the table), but you will get acquainted with this phenomenon a little later, and if you are interested, then read the 9th grade textbook.

The valency of elements must be known in order to compose chemical formulas of compounds. To do this, it is convenient to use the following table.

Table

Algorithm for composing the formula for the compound P and O

Sequencing

Formulating phosphorus oxide

1. Write the symbols of the elements

R O

2. Determine the valencies of elements

V II
P O

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

5 2 = 10

4. Find the relationships between atoms of elements by dividing the found smallest multiple by the corresponding valencies of the elements

10: 5 = 2, 10: 2 = 5;

P:O=2:5

5. Write indices for element symbols

R 2 ABOUT 5

6. Formula of the compound (oxide)

R 2 ABOUT 5

Teacher. Remember two more rules for drawing up chemical formulas for compounds of non-metals with each other.

1) The lowest valence is shown by the element that is located to the right and above in D.I. Mendeleev’s table, and the highest valence is shown by the element located to the left and below. (Demonstration of D.I. Mendeleev’s table.)

For example, in combination with oxygen, sulfur exhibits the highest valency VI, and oxygen the lowest valency II. Thus, the formula for sulfur oxide would be SO 3.

In the compound of silicon with carbon, the first exhibits the highest valency IV, and the second - the lowest IV. So the formula – SiC.This is silicon carbide, the basis of refractory and abrasive materials.

2) In the formulas of compounds, the non-metal atom exhibiting the lowest valency always comes in second place, and the name of such a compound ends in “id”.

For example, Sao– calcium oxide, NaCl- sodium chloride, PbS– lead sulfide.

Now you can write the formulas for any compounds of metals and non-metals.

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.

Exercise 1. Check whether the formulas of the following compounds are written correctly: Na 2 S, KBr, Al 2 O 3 ,
Mg 3 N 2 , MgO.

Task 2. 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. The teacher can selectively check some notebooks and praise those students who did it the fastest and made the fewest mistakes.

Consolidation of learned material

Conversation with students on issues

1) What is valency?

2) Why is valence sometimes called the atomicity of an element?

3) What are the valencies of hydrogen and oxygen?

4) What two valence values ​​can nonmetals exhibit?

5) How to determine the lowest and highest valence of non-metals?

6) How to find the least common multiple between the numerical values ​​of valences?

7) Can atoms in a compound have free valencies?

8) Which of the two non-metals in the chemical formula of their compound occupies 1st place, and which -
2nd? Explain using the example of NO oxide 2 , using the table of D.I. Mendeleev.

Creative work in groups

Exercise . 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, provides an analysis of the errors.

Homework assignment. According to the textbook “Chemistry-8” by L.S. Guzey: § 3.1, assignments No. 3, 4, 5, p. 51. Those who wish can prepare reports on the French scientist J.L. Proust and the English scientist J. Dalton.

Reflective-evaluative stage and summing up the lesson

Announce grades for the lesson to the students who responded, thank everyone for their work in the lesson. Assess your emotional state using the scale (see figure). The teacher once again reminds students of questions that need to be thought about in order to work effectively in the next lesson.

Literature

Guzey L.S., Sorokin V.V., Surovtseva R.P. Chemistry-8, M.: Bustard, 2000;Tyldsepp A.A., Kork V.A. We are studying chemistry. M.: Education, 1988;Bukreeva R.V., Bykanova T.A. Lessons on new technologies in chemistry. Voronezh, 1997.

DEFINITION

Under valence refers to the property of an atom of a given element to attach or replace a certain number of atoms of another element. A measure of valence can therefore be the number of chemical bonds formed by a given atom with other atoms.

Thus, at present, the valency of a chemical element is usually understood as its ability (in a narrower sense, a measure of its ability) to form chemical bonds. In the valence bond method representation, the numerical value of valence corresponds to the number of covalent bonds that an atom forms.

Drawing up chemical formulas by valency

Using chemical symbols based on the valence of elements, you can create a formula for a complex substance. To do this you need to know:

— chemical signs of the elements that make up the complex substance;

— valence of elements;

- be able to find the least common multiple of the valences of elements;

— determine indices for atoms of elements.

Let's consider the rules for compiling chemical formulas of complex compounds by valency using the example of inorganic substances of different classes:

a) oxides

Suppose we need to derive the formula for iron (III) oxide. To do this you need to do the following:

- depict the chemical symbols of the elements that make up a complex substance:

— let’s put the valency in Roman numerals above the sign of each element:

— find the smallest common multiple of the numbers of valence units:

— divide the least common multiple by the number of valence units of each element separately (the resulting quotients will be indices in the formula):

b) bases, salts and acids

When composing the formulas of bases and salts, use the same steps as when composing the formulas of oxides. The only difference is that instead of the oxygen atom there will be a hydroxo group (OH) or acidic residues (SO 4, SO 3, CO 3, NO 3, PO 4, SiO 3, S, Cl, etc.).

Suppose we need to derive the formula for calcium hydroxide:

common multiple of II × I = 2

2 / 2 = 1 (one is not included);

2 / 1 = 2 (OH should be in parentheses);

Examples of problem solving

EXAMPLE 1

Exercise	Determine the valence of elements in the following compounds: a) Mg 3 P 2 ; b) Al 2 S 3; c) Na 2 O; d) AgCl; e) FeCl 3.
Solution	Determining the valences of elements in a chemical compound should begin by indicating the valency of the known element. In option “a” it is magnesium, since elements of group IIA have a constant valence value equal to the group number, i.e. II. Let's write down the formula of the substance and indicate in Roman numerals the valency of the known element: We find the smallest multiple of the numbers of valency units. To do this, we multiply the magnesium valence value by the number of atoms of this element in compound (3): To determine the valence of phosphorus, divide the smallest multiple of the number of valency units by the number of phosphorus atoms in compound (2): This means that the valency of phosphorus is III: Mg II 3 P III 2 . Similarly, we determine the valences of elements in other compounds: b) Al III 2 S II 3; c) Na I 2 O II; d) Ag I Cl I ; e) Fe III Cl I 3.
Answer	a) Mg II 3 P III 2; b) Al III 2 S II 3; c) Na I 2 O II; d) Ag I Cl I ; e) Fe III Cl I 3

EXAMPLE 2

Exercise	Determine the valence of elements in the following compounds: a) CuO; b) Au 2 O; c) PbO 2; d) Li 3 N; e) AlF 3.
Solution	Determining the valences of elements in a chemical compound should begin by indicating the valence of the known element. In option “a” it is oxygen, since its valence is always equal to II: We put the resulting value to the right of the chemical symbol of this element, denoting it in Arabic numerals: Now we divide the total number of valence units by the number of atoms (index) of the element for which the valence is known: Let us place the resulting quotient (2) with a Roman numeral above the desired element as its valence: This means that the valence of the elements in the CuO compound is equal: for copper - II and for oxygen - II. Similarly, we determine the valences of elements in other compounds: b) Au I 2 O II; c) Pb IV O II 2; d) Li I 3 N II; e) Al III F I 3.
Answer	a) Cu II O II; b) Au I 2 O II; c) Pb IV O II 2; d) Li I 3 N II; e) Al III F I 3

Atomic-molecular science. Atoms. Molecules. Molecular and non-molecular structure of matter. Relative atomic and molecular mass. The law of conservation of mass, its significance in chemistry. A mole is a unit of quantity of a substance. Molar mass. Avogadro's law and the molar volume of gas. Relative density of matter.

Chemistry subject. Chemical and physical phenomena.

Chemistry is the science of substances and their transformations. She studies the composition and structure of substances, the dependence of their properties on their structure, the conditions and methods of converting some substances into others.

Chemistry is of great practical importance. Many thousands of years ago, man used chemical phenomena to smelt metals from ores, obtain alloys, melt glass, etc. Back in 1751. M.V. Lomonosov in his famous “Sermon on the Benefits of Chemistry” wrote: “Chemistry spreads its hands widely into human affairs. Wherever we look, wherever we look, the successes of its application appear before our eyes.”

Nowadays, the role of chemistry in the life of society is immeasurable. Chemical knowledge has now reached such a level of development that, on its basis, ideas about the nature and mechanism of a number of the most important natural and technological processes are radically changing. Chemistry has helped us discover and use not only previously unknown properties of substances and materials, but also to create new substances and materials that do not exist in nature.

Substance is a type of matter that, under certain conditions, has constant physical properties. However, as conditions change, the properties of the substance change.

Any changes that occur with matter are called phenomena. Phenomena are both physical and chemical.

Physical phenomena are those that lead to a change in the shape, state of aggregation, and temperature of a substance without changing its composition. The chemical composition of a substance does not change as a result of a physical phenomenon. For example, water can be turned into ice, into steam, but its chemical composition remains the same.

Chemical phenomena are those in which a radical change in the composition and properties of substances occurs. As a result of chemical phenomena, the transformation of some substances into others occurs, i.e. the composition of molecules changes, molecules of another substance are formed. However, atoms remain unchanged during chemical reactions. An example is the decomposition of limestone:

CaCO3 → CaO + CO2

Chemical phenomena are otherwise called chemical reactions. Characteristic signs of chemical phenomena (reactions): release of heat, gas, precipitation, color change, odor. This cannot be observed in physical phenomena.

The theoretical basis of modern chemistry is atomic-molecular science.

Atoms are the smallest chemical particles that are the limit of chemical decomposition of any substance.

A chemical element is a type of atom with the same positive nuclear charge.

Hence, an atom is the smallest particle of a chemical element that retains all its chemical properties. Currently, 110 elements are known, of which 92 occur in nature.

Depending on the nature of the particles from which the substance is built, substances with molecular and non-molecular structures are distinguished. Almost all organic substances (that is, the vast majority of known substances) are composed of molecules. Among inorganic compounds, approximately 5% have a molecular structure. Thus, the most typical form of existence of a substance is a molecule.

A molecule is the smallest particle of a substance that can exist independently and retain its basic chemical properties.

Under normal conditions, substances with a molecular structure can exist in a solid, liquid or gaseous state. Substances with a non-molecular structure are found only in the solid state, mainly in crystalline form. The carriers of the chemical properties of such substances are not molecules, but combinations of atoms or ions that form a given substance.

The symbolic notation of the simplest numerical relationship in which atoms of different elements form a chemical compound is called formula. Consequently, the formula expresses the specific (qualitative and quantitative) composition of the compound. So, SO2, N2, CO are the formulas of substances with a molecular structure. Their composition is always strictly constant. NaCl, AlF3, ZnS are the formulas of substances that do not have a molecular structure under normal conditions. The composition of such substances is not always constant and often depends on the conditions of their production. Deviations from the integer ratio can be expressed by writing the formula: Fe0.9S, TiO0.7, ZrN0.69. Substances with a constant composition are called colorblind, substances with variable composition - berthollides.

The masses of atoms of chemical elements are extremely small. In chemistry, they do not use their absolute values, but their relative ones.

The relative atomic mass of a chemical Ar element is a value equal to the ratio of the average mass of atoms of a given element (taking into account the percentage of its isotopes in nature) to 1/12 of the mass of carbon isotopes - 12. 1\12 of the mass of an atom of carbon isotope 12 is taken as atomic mass unit(a.u.m.), international designation - u.

Relative atomic mass is a dimensionless quantity.

The relative molecular mass Mr of a substance is the ratio of the mass of its molecule to 1/12 of the mass of an atom of the carbon isotope 12.

Since most inorganic substances under normal conditions do not have a molecular structure, in this case we can talk about formula mass F, meaning by it the sum of the atomic masses of all elements included in the compound, taking into account the number of atoms of each element in the formula.

The unit for measuring the amount of substance n (ν) in the International System of Units is mole.

Mole is the amount of substance containing as many structural elementary units (atoms, ions, molecules, electrons, equivalents, etc.) as there are atoms in 0.012 kg of the carbon 12 isotope.

The number of NA atoms in 0.012 kg of carbon (i.e. in 1 mol) is easy to determine, knowing the mass of the carbon atom. The exact value of this value is 6.02·10²³. This quantity is called Avogadro's constant and is one of the most important universal constants. It is equal to the number of structural units in 1 mole of any substance.

The mass of 1 mole of substance X is called molar mass M(X) is the ratio of the mass m of this substance to its quantity n.

Law of Conservation of Mass: “The mass of substances that entered into a chemical reaction is equal to the mass of substances formed as a result of the reaction, taking into account the mass corresponding to the thermal effect of the reaction.” It was formulated by the great Russian scientist M.V. Lomonosov in 1748. and confirmed experimentally by himself in 1756. and independently of him by the French chemist A.L. Lavoisier in 1789.

Law of constancy of the composition of matter: “Any complex substance of molecular structure, regardless of the method of production, has a constant quantitative composition.”

Avogadro's Law: “Equal volumes of different gases under the same conditions contain the same number of molecules.”

Consequences: 1. If the number of molecules of some gases is equal, then at no. they occupy equal volumes. If the number of molecules is 6.02·10²³, then the volume of the gas is 22.4 liters. This volume is called molar volume.

1. The absolute density of a gas is equal to the ratio of its molecular mass to its molar volume

2. The relative density of a gas (X) to another gas (Y) is equal to the ratio of the molar mass of the gas (X) to the molar mass of the gas (Y).

Claperon equation:

Boyle-Marriott equation:

Charles-Gay-Lusac equation:

Chemical element. Simple and complex substances. Chemical formulas.

A type of atom with the same chemical properties is called an element. Atoms of the same element can differ only in mass. Their chemical properties are the same. There are varieties of atoms of the same element called isotopes.

The concept of “chemical element” equally refers to atoms of a given element, both in free form and those included in compounds.

Molecules are formed from atoms. Depending on whether the molecule consists of atoms of the same element or of atoms of different elements, all substances are divided into simple and complex.

Simple substances are those whose molecules consist of atoms of one element. Molecules of simple substances can consist of one, two or more atoms of one element. At present, it is undeniable that the same element exists in a free state in the form of a number of different forms, i.e. in the form of several simple substances.

The existence of an element in the form of several simple substances is called allotropy. Simple substances formed by the same element are called allotropic modifications this element. These modifications differ both in the number and arrangement of the same atoms in the molecule.

Complex substances or chemical compounds are those whose molecules consist of atoms of two or more elements. Atoms that enter into a chemical compound do not remain unchanged. They influence each other mutually. In different molecules, atoms are in different states.

A chemical formula is a representation of the composition of a substance using chemical symbols. Chemical formulas indicate the molecule of a substance, its qualitative and quantitative composition.

An important concept in chemistry is valence . Valency is the ability of an atom to connect with other atoms through a certain number of chemical bonds. The numerical value of valency is determined by the total number of atomic orbitals involved in the formation of a chemical bond:

↓
		↓	↓

CO: C≡O C: 1s 2 2s 2 2p 2 valence: 3

O: 1s 2 2s 2 2p 4

All of the above applies to compounds with covalent bonds. If an element forms ionic bonds, its valence is called stoichiometric. It says nothing about the number of connections. The highest valence is equal to the number of the group in which the element is located, however, N, O and F have the highest valency - 4. This is explained by the fact that the atoms of these elements cannot go into an excited state due to the lack of vacant orbitals in the wind turbine.

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

DURING THE CLASSES

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 “valence” (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. “Valence 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 valency 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

Assignment 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

Assignment 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

Procedure

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.

Topic No. 11 “Drawing up chemical formulas by valency.”

1. Nomenclature of binary compounds.

Complex substances consisting of two elements, one of which is:

Bromides

NaBr

Chlorides

AlCl₃

Oxides

Sulfides

Nitrides

Ca₃N₂

Yodides

Hydrides

Name the substances: CrCl₃, MnO₂, H₂O, Li₂S, SO₃, Ca₃N₂, BaO, FeCl₃.

1. Fill in the missing words in the phrases:

1. water contains two......hydrogen and oxygen.
2. The human body contains a large amount of………. elements.
3. ...sulfuric acid H₂ SO ₄ consist of two….hydrogen, one…. sulfur and four.....oxygen.
4. …. aluminum chloride consists of….two……..
5. ......water is part of all living organisms.
6. …. nitrogen forms complex organic substances proteins.
7. Chemical……. aluminum is the second most abundant element in the earth's crust.

1. Make up the formulas:

Carbon(II) monoxide - cobalt(II) chloride

Carbon (IV) monoxide - iron (III) nitride

Phosphorus(III) chloride - copper(II) sulfide

Aluminum bromide - manganese (VII) oxide

Magnesium iodide - chromium (III) oxide

Potassium hydride - calcium hydride

W. Determine the valences of chemical elements in NH formulas₃ and CaO and create a formula for the compound of calcium and nitrogen in which they exhibit the same valency. Name all three substances found in the task.

D/z. 1. Determine the valence of elements in compounds: KClO₃, AlPO₄, CaCO₃, FeSO₄