One of the basic laws of chemistry, discovered in 1799 by J. L. Proust; According to this law, a certain chemically pure compound, regardless of the method of its preparation, consists of the same chemicals. elements having constant composition and properties... ... Big Polytechnic Encyclopedia

law of constancy of composition- pastoviųjų santykių dėsnis statusas T sritis fizika atitikmenys: engl. law of constant proportions; law of definite composition vok. Gesetz der konstanten Gewichtsverhältnisse, n; Gesetz der konstanten Proportionen, n; Gesetz der konstanten… … Fizikos terminų žodynas

law of constancy of composition- law of shares... Dictionary of chemical synonyms I

CONSTANTITY OF COMPOSITION LAW: every chemical compound, regardless of the method of its preparation, consists of the same elements, and the ratios of their masses are constant. Strictly applicable to gaseous and liquid compounds. Composition of crystalline... ... Big Encyclopedic Dictionary

CONSTANTITY OF COMPOSITION LAW: every chemical compound, regardless of the method of its preparation, consists of the same elements, and the ratios of their masses are constant. Strictly applicable to gaseous and liquid compounds. Composition of crystalline... ... encyclopedic Dictionary

In each specific chem. comp., regardless of the method of its preparation, the mass ratios of the constituent elements are constant. Formulated in the beginning. 19th century J. Proustome: A compound is a privileged product to which nature has given a constant composition.… … Chemical encyclopedia

One of the basic laws of chemistry: each specific chemical compound, regardless of the method of its preparation, consists of the same elements, and the ratios of their masses are constant, and the relative quantities of their atoms are expressed... ... Great Soviet Encyclopedia

One of the main laws of chemistry, which consists in the fact that every chemical. a compound, regardless of the method of its preparation, consists of the same chemicals. elements connected to each other in the same relationships (by mass). P.S. h. Was installed… … Big Encyclopedic Polytechnic Dictionary

Each chemical compound, regardless of the method of its preparation, consists of the same elements, and the ratios of their masses are constant. Strictly applicable to gaseous and liquid compounds. The composition of crystalline compounds can be... ... encyclopedic Dictionary

Each chem. a compound, regardless of the method of its preparation, consists of the same elements, and the ratios of their masses are constant. Strictly applicable to gaseous and liquid compounds. Composition crystalline conn. It may also be non-belt (see... ... Natural science. encyclopedic Dictionary

This lesson is devoted to the study of the law of constancy of the composition of matter. From the lesson materials you will learn who discovered this law.

I. Discovery of the law of constancy of the composition of matter

The basic laws of chemistry include the law of constancy of composition:

Any pure substance, regardless of the method of its preparation, always has a constant qualitative and quantitative composition.

Atomic-molecular theory makes it possible to explain the law of constancy of composition. Since atoms have a constant mass, the mass composition of the substance as a whole is constant.

The law of constancy of composition was first formulated by French chemist J. Proust in 1808

He wrote: "From one pole of the Earth to the other, the compounds have the same composition and the same properties. There is no difference between iron oxide from the Southern Hemisphere and the Northern. Malachite from Siberia has the same composition as malachite from Spain. There is only one cinnabar in the whole world."

This formulation of the law, as well as the one above, emphasizes the constancy of the composition of the compound, regardless of the method of preparation and location.

To obtain iron (II) sulfide FeS, we mix iron and sulfur in a ratio of 7:4.

If you mix them in a different proportion, for example 10:4, then chemical reaction will occur, but 3 g of iron will not react. Why is this pattern observed? It is known that in iron (II) sulfide there is one sulfur atom for every one iron atom. Therefore, for the reaction it is necessary to take substances in such mass ratios that the ratio of iron and sulfur atoms is maintained (1: 1). Because the numerical values atomic masses Fe, S and their relative atomic masses A r(Fe), A r(S) coincide, we can write: A r(Fe) : A r(S) = 56:32 = 7:4.
The ratio 7:4 remains constant, no matter in what units of mass the mass of substances is expressed (g, kg, t, amu). Majority chemical substances has a constant composition.

The development of chemistry has shown that, along with compounds of constant composition, there are compounds of variable composition.

Substances with variable composition exist; they were named after Berthollet - berthollides.

Berthollides- compounds of variable composition that do not obey the laws of constant and multiple ratios. Berthollides are non-stoichiometric binary compounds of variable composition, which depends on the method of preparation. Numerous cases of the formation of berthollides have been discovered in metal systems, as well as among oxides, sulfides, carbides, hydrides, etc. For example, vanadium(II) oxide can have a composition from V0.9 to V1.3, depending on the production conditions.

At the suggestion of N.S. Kurnakov were the first to be named colorblind(in memory of the English chemist and physicist Dalton), the second - berthollides(in memory of the French chemist Berthollet, who foresaw such compounds). The composition of daltonides is expressed simple formulas with integer stoichiometric indices, for example H 2 O, HCl, CCl 4, CO 2. The composition of berthollides varies and does not correspond to stoichiometric relationships.

Due to the presence of compounds of variable composition, clarification should be made to the modern formulation of the law of constancy of composition.

Composition of compounds molecular structure, i.e. consisting of molecules - is constant regardless of the method of production. The composition of compounds with a non-molecular structure (with an atomic, ionic and metal lattice) is not constant and depends on the conditions of preparation.

II. Problem solving

Based on the law of constancy of composition, various calculations can be made.

Task No. 1
In what mass ratios are the chemical elements combined in sulfuric acid, the chemical formula of which is H 2 SO 4?

Solution:

Ar(H)=1, Ar(S)=32, Ar(O)=16.
Let us determine the mass ratios of these elements in the formula H 2 SO 4
m(H) : m(S) : m(O) = 2Ar(H) : Ar(S) : 4Ar(O) = 2: 32: 64 = 1: 16: 32

Thus, to obtain 49 g of sulfuric acid (1+16+32=49), you need to take 1 g - H, 16 g - S and 32 g - O.

Task No. 2
Hydrogen combines with sulfur in a mass ratio of 1:16. Using data on the relative atomic masses of these elements, derive the chemical formula of hydrogen sulfide.

Solution:
Using PSHE we will find the relative atomic masses of chemical elements:
Ar(H)=1, Ar(S)=32.
Let's denote the number of hydrogen atoms in the formula - x, and sulfur - y: H x S y
m(H) : m(S) = xAr(H) : yAr(S) = x1: y32 = (2*1) : (1*32) = 2: 32 = 1: 16
Therefore, the formula of hydrogen sulfide H 2 S

Task No. 3
Derive the formula of copper sulfate if the mass ratios of copper, sulfur and oxygen in it are respectively 2:1:2?

Solution:
Using PSHE we will find the relative atomic masses of chemical elements:
Ar(Cu)=64, Ar(S)=32, Ar(O)=16.
Let us denote the number of copper atoms in the formula - x, sulfur - y, and oxygen - z: Cu x S y O z
m(Cu) : m(S) : m(O) = xAr(Cu) : yAr(S) : zAr(O) = x64: y32: z16 = (1*64) : (1*32) : (4 *16) = 64:32:64 = 2:1:2

III. Control tasks

No. 1. Using information about the relative atomic masses of chemical elements, calculate the mass ratios of the elements in carbonic acid, the chemical formula of which is H 2 CO 3.

No. 2. Determine the mass of oxygen that reacts without a residue with 3 g of hydrogen, if hydrogen and oxygen are in in this case are connected respectively in a ratio of 1: 8?

No. 3. Carbon and oxygen in carbon dioxide combine in mass ratios of 3:8.
Derive the chemical formula of carbon dioxide

No. 4. Determine the mass of hydrogen that reacts without a residue with 48 g of oxygen, if hydrogen and oxygen in this case are combined in a ratio of 1:8.

Chemistry belongs to the category of exact sciences, and along with mathematics and physics, it establishes the laws of the existence and development of matter, consisting of atoms and molecules. All processes occurring both in living organisms and among objects inanimate nature, are based on the phenomena of transformation of mass and energy. substance, the study of which this article will be devoted to, underlies the occurrence of processes in the inorganic and organic world.

Atomic-molecular science

To understand the essence of the laws governing material reality, you need to have an idea of ​​what it consists of. According to the great Russian scientist M.V. Lomonosov, “Physicists and, especially, chemists must remain in darkness, not knowing the internal particles of the structure.” It was he who, in 1741, first theoretically and then confirmed by experiments, discovered the laws of chemistry that serve as the basis for the study of living and inanimate matter, namely: all substances consist of atoms capable of forming molecules. All these particles are in continuous motion.

Discoveries and mistakes of J. Dalton

50 years later, Lomonosov’s ideas began to be developed by the English scientist J. Dalton. The scientist performed the most important calculations to determine the atomic masses of chemical elements. This served as the main proof of such assumptions: the mass of a molecule and substance can be calculated by knowing the atomic weight of the particles that make up its composition. Both Lomonosov and Dalton believed that, regardless of the method of preparation, the molecule of the compound will always have an unchanged quantitative and high-quality composition. Initially, it was in this form that the law of the constancy of the composition of matter was formulated. Recognizing Dalton's enormous contribution to the development of science, one cannot remain silent about annoying mistakes: denial molecular structure simple substances such as oxygen, nitrogen, hydrogen. The scientist believed that only complex molecules have molecules. Considering Dalton’s enormous authority in scientific circles, his misconceptions negatively affected the development of chemistry.

How atoms and molecules are weighed

The discovery of such a chemical postulate as the law of constancy of the composition of matter became possible thanks to the idea of ​​conservation of the mass of substances that entered into a reaction and were formed after it. In addition to Dalton, the measurement of atomic masses was carried out by I. Berzelius, who compiled a table of atomic weights of chemical elements and proposed their modern designation in the form of Latin letters. Currently, the mass of atoms and molecules is determined using the results obtained in these studies confirm the existing laws of chemistry. Previously, scientists used a device such as a mass spectrometer, but the complicated weighing technique was a serious drawback in spectrometry.

Why is the law of conservation of mass of substances so important?

The above-mentioned chemical postulate formulated by M.V. Lomonosov proves the fact that during a reaction, the atoms that make up the reactants and products do not disappear anywhere and do not appear from nothing. Their number remains unchanged before and after. Since the mass of atoms is constant, this fact logically leads to the law of conservation of mass and energy. Moreover, the scientist declared this pattern as a universal principle of nature, confirming the interconversion of energy and the constancy of the composition of matter.

The ideas of J. Proust as confirmation of the atomic-molecular theory

Let us turn to the discovery of such a postulate as the law of constancy of composition. Chemistry of the late 18th - early 19th centuries is a science within which scientific disputes were conducted between two French scientists, J. Proust and C. Berthollet. The first argued that the composition of substances formed as a result of a chemical reaction depends mainly on the nature of the reagents. Berthollet was sure that the composition of compounds - reaction products is also influenced by the relative amount of substances interacting with each other. Most chemists at the beginning of their research supported the ideas of Proust, who formulated them as follows: composition complex connection always constant and does not depend on how it was obtained. However, further study of liquid and solid solutions (alloys) confirmed the thoughts of K. Berthollet. The law of constancy of composition was not applicable to these substances. Moreover, it does not work for compounds with ionic crystal lattices. The composition of these substances depends on the methods by which they are extracted.

Each chemical substance, regardless of the method of its production, has a constant qualitative and quantitative composition. This formulation characterizes the law of constancy of the composition of matter, proposed by J. Proust in 1808. As evidence, he gives the following figurative examples: malachite from Siberia has the same composition as the mineral mined in Spain; There is only one substance in the world, cinnabar, and it does not matter from which deposit it is obtained. Thus, Proust emphasized the constancy of the composition of a substance, regardless of the place and method of its extraction.

There are no rules without exceptions

From the law of constancy of composition it follows that when a complex compound is formed, chemical elements are combined with each other in certain weight ratios. Soon in chemical science information appeared about the existence of substances having a variable composition, which depended on the method of preparation. The Russian scientist M. Kurnakov proposed calling these compounds berthollides, for example titanium oxide, zirconium nitride.

In these substances, for 1 part by weight of one element there is a different amount of another element. Thus, in the binary compound of bismuth with gallium, one part by weight of gallium accounts for from 1.24 to 1.82 parts of bismuth. Later, chemists found that, in addition to the combination of metals with each other, there are substances that do not obey the law of constancy of composition, such as oxides. Berthollides are also characteristic of sulfides, carbides, nitrides and hydrides.

The role of isotopes

Having at its disposal the law of constancy of matter, chemistry as exact science was able to link the weight characteristics of a compound with the isotopic content of the elements that form it. Let us remember that isotopes are considered to be atoms of the same chemical element with the same proton numbers but different nucleon numbers. Considering the presence of isotopes, it is clear that the weight composition of a compound can be variable, provided that the elements included in this substance are constant. If an element increases the content of any isotope, then the weight composition of the substance also changes. For example, ordinary water contains 11% hydrogen, and heavy water, formed by its isotope (deuterium), contains 20%.

Characteristics of Berthollides

As we have already found out earlier, the laws of conservation in chemistry confirm the basic provisions of the atomic-molecular theory and are absolutely true for substances of constant composition - daltonides. And Berthollides have boundaries within which changes in the weight parts of the elements are possible. For example, in tetravalent titanium oxide there is from 0.65 to 0.67 parts of oxygen per part by weight of the metal. Substances of variable composition are not composed of atoms in their crystal lattices. Therefore, the chemical formulas of compounds only reflect the boundaries of their composition. U various substances they are different. Temperature can also influence the range of changes in the weight composition of elements. If two chemical elements form several substances with each other - berthollides, then the law of multiple ratios is also not applicable to them.

From all the above examples, we can conclude: theoretically, there are two groups of substances in chemistry: with a constant and variable composition. The presence of these compounds in nature serves as excellent confirmation of the atomic-molecular theory. But the law of composition constancy itself is no longer dominant in chemical science. But it clearly illustrates the history of its development.

BASIC LAWS OF CHEMISTRY

Law of Conservation of Mass

The law of conservation of mass can be formulated as follows:

“the mass of substances entering into a chemical reaction is equal to the mass of substances formed as a result of the reaction.”

The discovery of this law is attributed to M.V. Lomonosov (1748 and confirmed experimentally by himself in 1756), although he himself did not attribute authorship to himself. In foreign literature, the discovery of this law is attributed to A. Lavoisier (1789)

This law is true with great accuracy for all chemical reactions, since the mass defect is disproportionately small

After the discovery of the special theory of relativity, mass acquired new properties:

1. The mass of an object depends on its internal energy. When energy is absorbed, mass increases; when energy is released, mass decreases. The change in mass is especially noticeable when nuclear reactions. During chemical reactions, the change in mass is negligible - when thermal effect reaction of 100 kJ/mol, the change in mass will be ~10 -9 g/mol; when an iron iron is heated by 200°, its mass increases by Δm/m~10 -12

2. Mass is not an additive quantity, that is, the mass of the system is not equal to the sum of the masses of its components, for example, the annihilation of an electron and a positron, particles with a rest mass of photons that do not have a rest mass, the mass of deuterium is not equal to the sum of the masses of a proton and a neutron, etc. d.

From the above it follows that the law of conservation of mass is closely related to the law of conservation of energy, which is explained by the special theory of relativity and is fulfilled with the same limitation - the exchange of energy between the system and the external environment must be taken into account.

Law of equivalents

Opened as a result chemical experiments I. Richter in 1791-1798

The original formulation of the law of equivalents (the term “equivalent” was introduced in 1767 by G. Cavendish) was as follows: “If the same amount of any acid is neutralized in different quantities two bases, then these quantities are equivalent and are neutralized by the same quantity of any other acid."

Simply put, chemical compounds interact not in arbitrary, but in strictly defined quantitative ratios.

However, this law opened the question of the constancy of the composition of the substance. The most prominent scientist of the time, Claude Louis Berthollet, proposed in 1803 the theory of chemical affinity, based on the forces of attraction and depending on the density of the substance and its quantity. He defended the assumption that the elemental composition of a substance could vary within certain limits depending on the conditions under which it was obtained. Permanent relationships in compounds, according to Bertholla, can only occur in cases where, during the formation of such compounds, a significant change in density and, consequently, adhesive forces occurred. Thus, hydrogen and oxygen gases combine to form water in constant ratios, because water is a liquid with a much higher density than the original gases. But if the change in density and cohesion during the formation of a compound is insignificant, substances of variable composition are formed within a wide range of ratios components. The boundaries for the formation of such compounds are the states of mutual saturation of the constituent parts. Berthollet's teaching, which rejected the constancy of proportions in chemical compounds, was met with obvious distrust despite Berthollet's high scientific authority. However, most analytical chemists, including such as Klaproth and Vauquelin, did not dare to openly refute Berthollet's statements. Only one, little-known Madrid chemist at that time, Proust, did not hesitate to criticize Berthollet’s views and point out his experimental errors and incorrect conclusions. After the appearance of Proust's first critical article (1801), Berthollet found it necessary to respond to the latter, defending his positions. An interesting and historically very important controversy ensued, which lasted several years (until 1808). And although Proust’s arguments, apparently, did not completely convince Berthollet, who back in 1809 recognized the possibility of the existence of compounds of variable composition, all chemists agreed on the point of view Proust, to whom belongs, therefore, the merit of the experimental establishment of the law of constancy of composition chemical compounds.

Law of Constancy of Composition

The law of constancy of composition (constant relationships) was discovered by the French scientist Joseph Louis Proust. And which became one of the main chemical laws.

Law of Constancy of Composition- any specific chemically pure compound, regardless of the method of its preparation, consists of the same chemical elements, and the ratios of their masses are constant, and the relative numbers of their atoms are expressed in integers.

Law of constancy of composition and stoichiometry of compounds for a long time were considered unshakable. However, at the beginning of the 20th century. I. S. Kurnakov, based on his research, came to the conclusion about the existence of non-stoichiometric compounds, i.e., characterized by variable composition. Even D.I. Mendeleev (1886), on the basis of his own observations and the numerous experimental data accumulated by that time, came to the conclusion that there are substances with a variable composition and that these compounds are real chemical compounds, only in a state of dissociation. N. S. Kurnakov noted that it would be a mistake to consider compounds of variable composition as something rare and exceptional. N. S. Kurnakov called permanent formations colorblind in honor of D. Dalton, who widely applied atomic-molecular theory to chemical phenomena. Nonstoichiometric compounds were named after C. Berthollet berthollides. According to his ideas, berthollides are peculiar chemical compounds of variable composition, the form of existence of which is not a molecule, but a phase, that is, a chemically bonded huge aggregate of atoms. Classical theory valence is not applicable for compounds of the berthollide type, since they are characterized by a variable valence that changes continuously rather than discretely. The listing of synthesized and known compounds suggests that most of them belong to the berthollide type. In principle, any solid compound, except substances with a molecular lattice, is a compound of variable composition.

Berthollides, according to Kurnakov, are solid solutions of chemical compounds of constant composition that are unstable in the free state. Having characterized compounds of constant and variable composition in this way, Kurnakov came to the conclusion that both Proust and Berthollet were right in their statements.

However, the simplicity of the composition of many Berthollides is recorded as constant. For example, the composition of iron(II) oxide is written as FeO (instead of the more precise formula Fe 1-x O).

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Law of Constancy
composition of the substance

Chemical formulas

Every substance – from the simplest
to the most complex - has three different,
but interconnected sides:
property, composition, structure...

B.M. Kedrov

Goals.
Didactic– consider the concepts of “chemical element”, “complex substance”, as well as the composition of complex substances, its constancy, what the chemical formula of a substance means, the purpose of coefficients and indices.
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. Crystal lattice of iron(II) sulfide, models of water molecules, individual cards for checking homework, anagram tablets for chemical warm-up, a scale for determining the emotional state of a student.

DURING THE CLASSES

Indicative-motivational stage

At the beginning and at the end of the lesson, a psychological warm-up is carried out. Its purpose is to determine the emotional state of students. Each student has inside A plate with six faces is glued to the cover of the notebook - a scale for determining emotional state(Fig. 1). Each student puts a tick under the face whose expression reflects his mood.

TEACHER. It would be great if by the end of the lesson everyone managed to move the check mark at least one square to the left. To do this, you need to think about the questions: can a person fall in love with someone who is uninteresting to him? academic subject? What do I need to do?

The article was published with the support of mobile online translator"m-translate.ru". Convenient and fast online translation from a dozen languages, thousands of translation directions. Does not require installation, translation of words, sentences and texts, free. To start using the service online translation go to the website: http://www.m-translate.ru/.

Chemical warm-up.
STUDENT.Vasya and Petya love to compose and solve anagram words (usually fantastic ones), in which the order of the letters is rearranged. Try to solve some of the chemical anagrams.
By rearranging the letters in each word, you need to get the name of the chemical element.
Leodrug– without this element there will be no fire in the stove,
slikodor– without this element you cannot live even ten minutes,
cinves– this element has a really high specific gravity,
mnikray– look for this element among the stones,
orrebes- glitters, not gold.
TEACHER.If you completed this task easily, tell yourself: “I am smart.”
Examination homework on the topic "Chemical signs". Repeat the signs of chemical elements and the values ​​of their relative atomic masses. Pay attention to the difference between the mass of an atom (in atomic mass units) and the relative atomic mass (dimensionless quantity) on their common feature– the same numerical value. Then carry out the frontal independent work on individual cards within 5–10 minutes.
Card 1. Name the elements by their chemical symbols: N, S, Ag, Al, O, I.
Card 2. Write the chemical symbols of the elements: iron, hydrogen, sodium, bromine, zinc, chlorine.

Operational and executive stage

TEACHER. Today we will get acquainted with one of the basic laws of chemistry - the law of constancy of the composition of matter. I would like you to see behind the strict wording of the law a living, hardworking and inquisitive man from France - Joseph Louis Proust. He spent seven years studying a variety of substances to prove a statement that, in modern formulation, fits in three lines. His fellow countryman, little known among us, spoke about this very beautifully in his poems French poet Armand Sully-Prudhomme, laureate Nobel Prize, contemporary of D.I. Mendeleev.
PUPIL
“The chemist’s gaze is inquisitive, order is dear to him,
Among its retorts, beakers and instruments,
So mysterious to prying eyes,
He strives to comprehend the whims of secret forces.
He has a lot of them already installed,
Watching their game, a participant in their strife,
And soon he commands, the ruler of these disputes,
Recognize and honor the law that he revealed.
I envy you, demanding scientist,
Whose keen eyes see the world naked,
Like the day of creation, the source of all other days.
Lead me to the mysterious kingdom!
I believe that only in him will a cure be found
From all the countless sorrows and sorrows.”

TEACHER. To obtain iron(II) sulfide, we mixed iron and sulfur in a ratio of 7:4. If you mix them in a different proportion, for example 10:4, then a chemical reaction will occur, but 3 g of iron will not react. Why is this pattern observed? It is known that in iron(II) sulfide there is one sulfur atom for every one iron atom Fe, S (demonstration of a crystal lattice, Fig. 2).(Fe), A r Therefore, for the reaction it is necessary to take substances in such mass ratios that the ratio of iron and sulfur atoms is maintained (1: 1). Since the numerical values ​​of atomic masses and their relative atomic masses A r A r(S) A r coincide, we can write:
(Fe):
(S) = 56:32 = 7:4.
The ratio 7:4 remains constant, no matter in what units of mass the mass of substances is expressed(g, kg, t, amu). Most chemicals have a constant composition.
Law of constancy of the composition of substances was discovered by the French scientist Proust in 1808. This is how this law sounded in his presentation: “From one pole of the Earth to the other, compounds have the same composition and the same properties. There is no difference between iron oxide from the Southern Hemisphere and the Northern Hemisphere. Malachite from Siberia has the same composition as malachite from Spain. There is only one cinnabar in the whole world."

Modern wording of the law : every chemically pure substance with a molecular structure, regardless of location and method of preparation, has the same constant qualitative and quantitative composition. Students write the definition in their notebook. Then they perform independent work
.. To obtain iron(II) sulfide, we took 3.5 g of iron and 4 g of sulfur. What substance will remain unused and what is its mass?
Option 2. To obtain iron(II) sulfide, we took 15 g of iron and 8 g of sulfur. What substance is taken in excess and what is the mass of this excess?

TEACHER. Now listen to a speech about the famous dispute between the French scientists J.L. Proust and C.L. Berthollet, which lasted about 10 years on the pages of French magazines in early XIX V.
STUDENT. Yes, the dispute between two French chemists lasted from 1799 to 1809, and then was continued by chemists in England, Sweden, Italy, Russia and other countries. This dispute can rightfully be called the first scientific discussion of such a scale both in terms of the time of its occurrence and the strategic importance of the problems discussed. This discussion determined the development of chemistry for centuries to come.
In 1799, Joseph Louis Proust, a French-born professor at the Royal Laboratory in Madrid, published the article “Research on Copper.” The article covers in detail the analyzes of copper compounds and makes a well-founded conclusion that a chemically individual compound always, regardless of the method of its formation, has a constant composition. Proust came to the same conclusion later, in 1800–1806, while studying the chemical compounds of lead, cobalt and other metals.
In 1800–1803 English chemist John Dalton substantiated this law theoretically, establishing atomic structure molecules and the presence of certain atomic masses of elements. Purely theoretically, Dalton came to the discovery of another fundamental law of chemistry - the law of multiple ratios, which is in unity with the law of constancy of composition.
At the same time, Claude Louis Berthollet, a professor at the Ecole Normale in Paris, already a famous chemist, published a number of articles in which he defended the conclusion that the composition of chemical compounds depends on the method of their preparation and is often not constant, but variable. Berthollet opposed the laws of Proust and Dalton, arguing this with more and more experiments on the production of alloys and solid metal oxides. He also used the data of Proust himself, pointing out that natural sulfides and oxides of metals contain an excess of sulfur and oxygen compared to those obtained in the laboratory.
The development of chemistry showed that both sides were right. Proust's and Dalton's perspective on chemistry in the 1800s. was clear, specific and almost obvious.
molecular teaching about the composition and structure of chemical compounds. This was the main line of development of chemistry. Berthollet's point of view was practically unacceptable for the chemistry of that time, since it reflected the chemistry of processes, the study of which began mainly only
since the 1880s And only the future showed that Berthollet was right!
At the suggestion of Academician N.S. Kurnakov, substances of constant composition were called daltonides (in honor of the English chemist and physicist Dalton), and substances of variable composition were called berthollides (in memory of the French chemist Bertholle). (You can read more about this in the works.)
TEACHER. Let's summarize the message.
Firstly, substances of non-molecular structure with variable composition are known. Secondly, the law of constancy of the composition of substances is valid for substances of molecular structure. Thirdly, there is a category of substances of molecular structure for which the law of constancy of composition is incorrect. These are polymers, we will get acquainted with them in chemistry lessons later.
What is meant by quantitative and qualitative compositions of substances? Based on Proust's law, chemical formulas of substances can be written using chemical symbols.
Consider, as an example, the composition of a water molecule. It consists of hydrogen and oxygen atoms (qualitative composition), and by weight water contains hydrogen - 11.19%, and oxygen - 88.81% (quantitative composition). There are several ways to express the composition of water. 1st method
. A water molecule contains two hydrogen atoms and one oxygen atom (we use words). 2nd method
. The same idea can be expressed by drawing (we use symbols): 3rd method. Water formula – H 2 O
(we use chemical signs and indices). Index shows the number of atoms of this element
in a molecule. So, the composition of daltonides is expressed by simple formulas with integer stoichiometric indices, for example H 2 O, HCl, CH 4. The composition of berthollides is variable; they have fractional stoichiometric indices. Thus, titanium(II) oxide TiO actually has a composition of
TiO 0.7 to TiO 1.3. Answer me this question: what does the coefficient show? (
Student answer: the number of molecules of a given substance.) Consider an example: 3H 2 O. How many water molecules does this entry represent? How many hydrogen atoms are there in one molecule of water, in three molecules of water? How many oxygen atoms are there in one molecule of water, in three molecules of water? (Demonstration of models of water molecules.)
Demonstration of enlarged figure 15 on p. 24 textbooks "Chemistry-8" representing the entry: 3CuCl 2, 5Al 2 O 3, 3FeCl 2.
TEACHER. How to read the formulas of these substances? How many molecules of a given substance does the chemical formula show? How many atoms of each element are in one molecule of a given substance? How many atoms of each element are there in three (five) molecules of this substance?
Chemical formula is a conventional notation of the composition of a substance using chemical symbols and indices.
Students write the definition in their notebook.

Reflective-evaluative stage

Conversation with students for questions.
1. Who and when was the law of constancy of the composition of substances discovered?
2. Define this law.
3. What was the essence of the dispute between the chemists Proust, Dalton and Berthollet?
4. What does the chemical formula of a substance reflect?
5. What do the coefficients and indices show in chemical formula?
6. Is there a difference in the composition of substances with the formulas: CO and CO 2, H 2 O and H 2 O 2?
7. Using chemical symbols, indices and coefficients, write down the designations
two water molecules
three molecules of nitric oxide (if it is known that in a molecule of nitric oxide there are two oxygen atoms for one nitrogen atom),
three molecules of hydrogen sulfide (in its molecule there is one sulfur atom for every two hydrogen atoms),
four molecules of phosphorus oxide (in each molecule of this oxide there are five oxygen atoms for two phosphorus atoms).
Students make notes in their notebooks, one student writes on the back of the board. Checking: exchanging notebooks with your deskmate, checking the answer on the board, analyzing errors.
Homework assignment. Textbook "Chemistry-8", § 9, p. 22–23; § 10, p. 24–25. Two students are given the task of preparing short reports on the biography of Proust.
Lesson summary. 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 Fig. 1). The teacher once again reminds you of the questions that you need to think about in order to efficient work on lessons.

LITERATURE

1. Soloveichik S.L. The hour of apprenticeship. M.: Pedagogy, 1986.
2. Leenson I.A. Chemical elements and chemical laws. Workbook. M.: Gymnasium Publishing House " Open world", 1995.
3. Kuznetsov V.I., Rakhimbekova X. Discussions in the development of science and dialog form training.
4. Chemistry at school, 1991, No. 6. Kuznetsov V.I.
5. Evolution of ideas about the basic laws of chemistry. M.: Nauka, 1967. Rudzitis G.E., Feldman F.G.