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Law of constancy of the composition of matter. Laws of conservation in chemistry

Chemistry belongs to the category of exact sciences, and along with mathematics and physics 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 of inanimate nature, are based on the phenomenon of the transformation of mass and energy. The law of the constancy of the composition of matter, the study of which this article will be devoted to, is the basis of the processes in the inorganic and organic world.

Atomic-molecular teaching

To understand the essence of the laws governing material reality, one must have an idea of what it consists of. According to the great Russian scientist M. V. Lomonosov "In darkness, physicists and, especially, chemists must remain, not knowing the inner 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 studying living and inanimate matter, namely: all substances are composed of atoms capable of forming molecules. All these particles are in continuous motion.

Discoveries and errors of J. Dalton

After 50 years, the idea of Lomonosov began to develop the English scientist J. Dalton. The scientist carried out the most important calculations to determine the atomic masses of chemical elements. This served as the main proof of such assumptions: the mass of the molecule and matter can be calculated, knowing the atomic weight of the particles that make up its composition. Both Lomonosov and Dalton believed that, regardless of the method of production, the molecule of the compound will always have an unchanged quantitative and qualitative composition. Originally, it was in this form that the law of constancy of the substance composition was formulated. Recognizing Dalton's enormous contribution to the development of science, one can not keep silent about annoying mistakes: the negation of the molecular structure of simple substances such as oxygen, nitrogen, and hydrogen. The scientist believed that there are molecules only in complex chemical substances. Considering Dalton's enormous authority in the scientific community, his mistakes negatively affected the development of chemistry.

How do we weigh atoms and molecules

The discovery of such a chemical postulate as the law of the constancy of the composition of matter became possible due to the idea of the preservation of the mass of substances that reacted and formed after it. In addition to Dalton, the measurement of atomic masses was conducted by I. Berzelius, who compiled a table of atomic weights of chemical elements and proposed their modern designation in the form of Latin letters. At present, the mass of atoms and molecules is determined with the help of a carbon nanotube. 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 important?

The above-named chemical postulate formulated by MV Lomonosov proves the fact that during the reaction the atoms that make up the reagents and products do not disappear anywhere and do not appear from nothing. Their quantity remains unchanged before and after the chemical process. 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 regularity as a universal principle of nature, confirming the interconversion of energy and the constancy of the composition of matter.

Proust's ideas as confirmation of the atomic-molecular theory

Let us turn to the discovery of such a postulate as the law of constancy of the composition. Chemistry of the late 18th - early 19th centuries - a science within which scientific disputes were being fought between two French scientists, J. Proust and C. Berthollet. The first asserted that the composition of the substances formed as a result of the chemical reaction depends mainly on the nature of the reagents. Berthollet was sure that the relative number of interacting substances also influences the composition of the compounds-reaction products. Most chemists at the beginning of the research supported the ideas of Proust, who formulated them as follows: the composition of a complex compound is always permanent and does not depend on how it was received. However, further study of liquid and solid solutions (alloys) confirmed the thoughts of K. Berthollet. To these substances the law of constancy of composition was inapplicable. 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.

Every chemical substance, regardless of the method of its preparation, 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 cites the following figurative examples: malachite from Siberia has the same composition as the mineral mined in Spain; In the world there is only one cinnabar substance, and it does not matter from what field it was obtained. Thus, Proust emphasized the constancy of the composition of matter, regardless of the place and method of extraction.

There are no rules without exceptions

From the law of constancy of the composition, it follows that in the formation of a complex compound, the chemical elements are combined with each other in certain weight ratios. Soon in the chemical science information appeared on the existence of substances that have a variable composition, which depended on the method of production. Russian scientist M. Kurnakov suggested to call these compounds berthollides, for example titanium oxide, heavy water, zirconium nitride.

These substances have a different amount of another element per 1 part by weight of one element. Thus, in a binary compound of bismuth with gallium, one part by weight of gallium accounts for 1.24 to 1.82 parts of bismuth. Later chemists established that, in addition to combining metals with each other, substances that do not obey the law of constancy of composition are in this class of inorganic compounds, like oxides. Bertollides are also characteristic for sulphides, carbides, nitrides and hydrides.

The role of isotopes

Having received at his disposal the law of the constancy of matter, chemistry as an exact science could link the weight characteristic of a compound with the isotopic content of the elements that form it. Recall that isotopes consider atoms of one chemical element with identical proton, but different nucleon numbers. Taking into account the presence of isotopes, it is clear that the weight composition of the compound can be variable provided that the elements entering this substance are constant. If the element increases the content of any isotope, then the weight composition of the substance also changes. For example, ordinary water contains 11% hydrogen, and the heavy water, formed by its isotope (deuterium), is 20%.

Characteristics of berthollides

As we have already explained, the conservation laws in chemistry confirm the basic positions of the atomic-molecular theory and are absolutely true for substances of constant composition-daltonides. A berthollides have boundaries in which it is possible to change the weight parts of the elements. For example, in oxide of tetravalent titanium, one part by weight of the metal is from 0.65 to 0.67 parts of oxygen. The substances of a non-permanent composition do not have a molecular structure, their crystal lattices consist of atoms. Therefore, the chemical formulas of compounds only reflect the boundaries of their composition. Different substances are different. The temperature can also influence the intervals of change in the weight composition of the elements. If two chemical elements form several berthollides among themselves, then the law of multiple relations is also inapplicable for them.

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

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