During the nineteenth century, many areas underwent a strong reformation, including chemistry. Periodic theory, formulated in 1869, led to a unified understanding of the dependence of the position of simple substances in the periodic table, establishing the relationship between the relative atomic mass, valence and properties of the element.

Pre-Mendeleev period of chemistry

Somewhat earlier, at the beginning of the nineteenth century, repeated attempts were made to systematize. The German chemist Döbereiner carried out the first serious work on systematization in the field of chemistry. He determined that a number of similar substances according to their properties can be combined into groups - triads.

The fallacy of the ideas of the German scientist

The essence of the presented law of Döbereiner triads was determined by the fact that the atomic mass of the desired substance is close to the half-sum (average value) of the atomic masses of the last two elements of the triad table.

However, the absence of magnesium in a single subgroup of calcium, strontium and barium was erroneous.

This approach was a consequence of the artificial limitation of similar substances to only triple alliances. Döbereiner clearly saw the similarities in the chemical parameters of phosphorus and arsenic, bismuth and antimony. However, he limited himself to finding triads. As a result, he was unable to come to the correct classification chemical elements.

Döbereiner certainly failed to divide existing elements into triads; the law clearly indicated the presence of a relationship between and the properties of simple chemical substances.

The process of systematizing chemical elements

All subsequent attempts at systematization were based on the distribution of elements depending on their atomic mass. Subsequently, Döbereiner's hypothesis was used by other chemists. The formation of triads, tetrads and pentads (combining into groups of three, four and five elements) appeared.

In the second half of the nineteenth century, several works appeared simultaneously, based on which Dmitry Ivanovich Mendeleev led chemistry to a full systematization of chemical elements. A different structure of Mendeleev's periodic system led to a revolutionary understanding and obviousness of the mechanism of distribution of simple substances.

Mendeleev's periodic table of elements

At a meeting of the Russian chemical community in the spring of 1869, a notice was read from the Russian scientist D.I. Mendeleev about his discovery of the periodic law of chemical elements.

In November 1870, he showed his colleagues the addition “The Natural System of Elements and its Use in Indicating the Qualities of Undiscovered Elements.” In this work, D.I. Mendeleev first used the term “periodic law”. Mendeleev's system of elements, based on the periodic law, determined the possibility of the existence of undiscovered simple substances and clearly indicated their properties.

Corrections and clarifications

As a result, by 1971, the periodic law and Mendeleev’s periodic system of elements were finalized and supplemented

In the final article “Periodic Law of Chemical Elements,” the scientist established a definition of the periodic law, which states that the characteristics of simple bodies, the properties of compounds, as well as the complex bodies they form, are determined by a direct relationship according to their atomic weight.

Somewhat later, in 1872, the structure of Mendeleev’s periodic system was reorganized into the classical form (short-period distribution method).

Unlike his predecessors, the Russian chemist fully compiled a table and introduced the concept of regularities in the atomic weight of chemical elements.

The characteristics of the elements of Mendeleev’s periodic system and the derived patterns allowed the scientist to describe the properties of elements that have not yet been discovered. Mendeleev relied on the fact that the properties of each substance can be determined according to the characteristics of two neighboring elements. He called this the "star" rule. Its essence is that in the table of chemical elements, to determine the properties of the selected element, you need to navigate horizontally and vertically in the table of chemical elements.

Mendeleev's periodic table is able to predict...

The periodic table of elements, despite its accuracy and fidelity, was not fully recognized by the scientific community. Some great world-famous scientists openly ridiculed the possibility of predicting the properties of an undiscovered element. It was only in 1885, after the discovery of the predicted elements - eka-aluminum, eka-boron and eca-silicon (gallium, scandium and germanium), that Mendeleev's new classification system and the periodic law were recognized as the theoretical basis of chemistry.

At the beginning of the twentieth century, the structure of Mendeleev's periodic table was repeatedly adjusted. In the process of obtaining new scientific data, D. I. Mendeleev and his colleague U. Ramsay came to the conclusion that it was necessary to introduce a zero group. It included inert gases (helium, neon, argon, krypton, xenon and radon).

In nineteen hundred and eleven, F. Soddy made a proposal to place indistinguishable chemical elements - isotopes - in one cell of the table.

In the process of long and painstaking work, Mendeleev’s periodic table of chemical elements was finally finalized and acquired a modern look. It consisted of eight groups and seven periods. Groups are vertical columns, periods are horizontal. The groups are divided into subgroups.

An element's position in the table indicates its valence, net electrons, and chemical features. As it turned out later, during the development of the table, D.I. Mendeleev discovered a random coincidence of the number of electrons of an element with its atomic number.

This fact further simplified the understanding of the principle of interaction of simple substances and the formation of complex ones. And also the process in the opposite direction. Calculation of the amount of substance obtained, as well as that required for the chemical reaction to occur, has become theoretically available.

The role of Mendeleev's discovery in modern science

Mendeleev's system and his approach to the ordering of chemical elements predetermined the further development of chemistry. Thanks to a correct understanding of the relationship of chemical constants and analysis, Mendeleev was able to correctly arrange and group elements according to their properties.

The new table of elements makes it possible to clearly and accurately calculate data before the start of a chemical reaction, predict new elements and their properties.

The discovery of the Russian scientist had a direct impact on the further development of science and technology. There is no technological field that does not involve knowledge of chemistry. Perhaps, if such a discovery had not taken place, our civilization would have taken a different path of development.

DI. Mendeleev formulated the Periodic Law in 1869, which was based on one of the main characteristics atom – atomic mass. The subsequent development of the Periodic Law, namely, the acquisition of a large amount of experimental data, somewhat changed the original formulation of the law, but these changes do not contradict the main meaning laid down by D.I. Mendeleev. These changes only gave the law and the Periodic Table scientific validity and confirmation of correctness.

Modern formulation of the Periodic Law by D.I. Mendeleev is as follows: the properties of chemical elements, as well as the properties and forms of compounds of elements, are periodically dependent on the magnitude of the charge of the nuclei of their atoms.

Structure of the Periodic Table of Chemical Elements D.I. Mendeleev

By present opinion it is known a large number of interpretations of the Periodic Table, but the most popular is with short (small) and long (large) periods. Horizontal rows are called periods (they contain elements with sequential filling of the same energy level), and vertical columns are called groups (they contain elements that have the same number of valence electrons - chemical analogues). Also, all elements can be divided into blocks according to the type of external (valence) orbital: s-, p-, d-, f-elements.

There are a total of 7 periods in the system (table), and the period number (indicated Arabic numeral) is equal to the number of electronic layers in an element’s atom, the number of the external (valence) energy level, and the value of the principal quantum number for the highest energy level. Each period (except the first) begins with an s-element - an active alkali metal and ends with an inert gas, preceded by a p-element - an active non-metal (halogen). If you move through the period from left to right, then with an increase in the charge of the nuclei of atoms of chemical elements of small periods, the number of electrons at the external energy level will increase, as a result of which the properties of the elements change - from typically metallic (since at the beginning of the period there is an active alkali metal), through amphoteric (the element exhibits the properties of both metals and non-metals) to non-metallic (the active non-metal is halogen at the end of the period), i.e. metallic properties gradually weaken and non-metallic properties increase.

In large periods, as the charge of nuclei increases, the filling of electrons is more difficult, which explains a more complex change in the properties of elements compared to elements of small periods. Thus, in even rows of long periods, as the charge of the nucleus increases, the number of electrons in the outer energy level remains constant and equal to 2 or 1. Therefore, while the level next to the outer (second from the outside) is filled with electrons, the properties of the elements in the even rows change slowly. When moving to odd series, with increasing nuclear charge, the number of electrons in the external energy level increases (from 1 to 8), the properties of the elements change in the same way as in small periods.

Vertical columns in the Periodic Table are groups of elements with similar electronic structures and which are chemical analogues. Groups are designated by Roman numerals from I to VIII. There are main (A) and secondary (B) subgroups, the first of which contain s- and p-elements, the second - d-elements.

The number A of the subgroup shows the number of electrons in the outer energy level (the number of valence electrons). For B-subgroup elements, there is no direct connection between the group number and the number of electrons in the outer energy level. In A-subgroups, the metallic properties of elements increase, and non-metallic properties decrease with increasing charge of the nucleus of the element’s atom.

There is a relationship between the position of elements in the Periodic Table and the structure of their atoms:

- atoms of all elements of the same period have an equal number of energy levels, partially or completely filled with electrons;

- atoms of all elements of the A subgroups have an equal number of electrons at the outer energy level.

Periodic properties of elements

The proximity of physico-chemical and chemical properties atoms is due to the similarity of their electronic configurations, and the distribution of electrons over the outer atomic orbital plays a major role. This manifests itself in the periodic appearance, as the charge of the atomic nucleus increases, of elements with similar properties.

Such properties are called periodic, among which the most important are: 1. Number of electrons in the outer electron shell ( – population w population). In short periods with increasing nuclear charge population the outer electron shell monotonically increases from 1 to 2 (1st period), from 1 to 8 (2nd and 3rd periods). In large periods during the first 12 elements

2. does not exceed 2, and then up to 8.(r), defined as the average radii of an atom or ion, found from experimental data on interatomic distances in different compounds. According to the period, the atomic radius decreases (gradually adding electrons are described by orbitals with almost equal characteristics; according to the group, the atomic radius increases as the number of electron layers increases (Fig. 1.).

Rice. 1. Periodic change in atomic radius

The same patterns are observed for the ionic radius. It should be noted that the ionic radius of the cation (positively charged ion) is greater than the atomic radius, which in turn is greater than the ionic radius of the anion (negatively charged ion).

3. Ionization energy(E and) is the amount of energy required to remove an electron from an atom, i.e. the energy required to transform a neutral atom into a positively charged ion (cation).

E 0 - → E + + E and

E and is measured in electronvolts (eV) per atom. Within the group of the Periodic Table, the values ​​of ionization energy of atoms decrease with increasing charges of the atomic nuclei of elements. All electrons can be sequentially removed from atoms of chemical elements by reporting discrete values ​​of E and.< Е и 2 < Е и 3 <….Энергии ионизации отражают дискретность структуры электронных слоев и оболочек атомов химических элементов.

4. Moreover, E and 1 Electron affinity

(E e) – the amount of energy released when an additional electron is added to an atom, i.e.

process energy

5. E 0 + → E — E e is also expressed in eV and, like E, it depends on the radius of the atom, therefore the nature of the change in E e across periods and groups of the Periodic System is close to the nature of the change in the atomic radius. Group VII p-elements have the highest electron affinity.

6. Regenerative activity(VA) – the ability of an atom to give an electron to another atom. Quantitative measure – E and. If E increases, then BA decreases and vice versa.

7. Oxidative activity(OA) – the ability of an atom to attach an electron from another atom. Quantitative measure E e. If E e increases, then OA also increases and vice versa. Shielding effect– reducing the impact on a given electron of the positive charge of the nucleus due to the presence of other electrons between it and the nucleus. Shielding increases with the number of electron layers in an atom and reduces the attraction of outer electrons to the nucleus. The opposite of shielding

8. penetration effect– the imaginary charge of an atom of an element in a compound, which is determined from the assumption of the ionic structure of the substance. The group number of the Periodic Table indicates the highest positive oxidation state that elements of a given group can have in their compounds. Exceptions are metals of the copper subgroup, oxygen, fluorine, bromine, metals of the iron family and other elements of group VIII. As the nuclear charge increases in a period, the maximum positive oxidation state increases.

9. Electronegativity, compositions of higher hydrogen and oxygen compounds, thermodynamic, electrolytic properties, etc.

Examples of problem solving

EXAMPLE 1

Periodic law- the fundamental law of chemistry - was discovered in 1869 year DI. Mendeleev. At that time, the atom was still considered indivisible and nothing was known about its internal structure.

Atomic masses(Then - atomic weights) and the chemical properties of the elements were used as the basis Periodic law D.I. Mendeleev. DI. Mendeleev, arranging the 63 elements known at that time in increasing order of their atomic masses, obtained natural (natural) series of chemical elements, where he noted the periodic repeatability of chemical properties. For example, a typical nonmetal fluorine F repeated in elements chlorine Cl, bromine Br, iodine I, properties of a typical metal lithium Li – at the elements sodium Na And potassium K etc.

For some elements D.I. Mendeleev did not discover chemical analogues (in aluminum Al And silicon Si, for example), given that at that time such analogues were not yet known. In the table they were intended empty spaces, But based on periodic repetition scientist predicted their chemical properties). After discovering the corresponding elements of the prediction by D.I. Mendeleev were completely confirmed (analogue of aluminum - gallium Ga, analogue of silicon – germanium Ge).

The periodic law as formulated by D.I. Mendeleev is presented as follows: the properties of simple bodies, as well as the forms and properties of compounds of elements, depend periodically on the atomic weights of elements.

Modern formulation of the Periodic Law by D.I. Mendeleev sounds like this: the properties of the elements periodically depend on the serial number.

Periodic law D.I. Mendeleev became the basis for the creation of scientists Periodic Table of Chemical Elements. She is presented 7 periods and 8 groups.

Periods are called horizontal rows of the table, which are divided into small and large. 2 elements (1st period) or 8 elements (2nd, 3rd periods) are in small periods, and in large periods there are 18 elements (4th, 5th periods) or 32 elements (6th period), the 7th period remains unfinished. Every period starts with typical metal from ends in a typical non-metal and noble gas.

In groups elements are called vertical columns. Each group is represented by two subgroups - main And side. A subgroup is a set of elements that are complete chemical analogues; often elements of a subgroup have the highest oxidation state corresponding to the group number. For example, the highest oxidation state (+ II) corresponds to elements of the subgroup beryllium And zinc(main and secondary subgroups of group II), and the elements of the subgroup nitrogen And vanadium(V group) corresponds to the highest oxidation state (+ V).

The chemical properties of elements in the main subgroups can vary from non-metallic to metallic (in the main subgroup of group V, nitrogen is a non-metal, and bismuth is a metal) - over a wide range. The properties of elements in side subgroups change, but not so dramatically; for example, elements of the secondary group of group IV - zirconium, titanium, hafnium– very similar in their properties (especially zirconium And hafnium).

In the Periodic Table in Group I (Li – Fr), II (Mg – Ra) and III (In, Tl) typical metals are located. Nonmetals are located in groups VII (F – At), VI (O–Te), V (N–As), IV (C, Si) and III (B). Some elements of the main groups ( Be, Al, Ge, Sb, Po), as well as many elements of side groups can exhibit both metallic and non-metallic properties. This phenomenon is called amphotericity.

For some main groups, groups are used New names: VIII (He – Rn) – noble gases, VII (F – At) – halogens, IV (O – Ro) – chalcogens, II (Ca – Ra) – alkaline earth metals, I (Li – Fr) – alkali metals.

The form of the Periodic Table proposed by D.I. Mendeleev, was named short period, or classical. In modern chemistry, another form is increasingly used - long-period, in which all periods - small and large - are extended in long rows, starting with an alkali metal and ending with a noble gas.

Periodic law D.I. Mendeleev and the Periodic Table of Elements D.I. Mendeleev became the basis of modern chemistry.

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Periodic law of D.I. Mendeleev, its modern formulation. What is its difference from the one given by D.I. Mendeleev? Explain what caused this change in the wording of the law? What is the physical meaning of the Periodic Law? Explain the reason for the periodic changes in the properties of chemical elements. How do you understand the phenomenon of periodicity?

The periodic law was formulated by D.I. Mendeleev in the following form (1871): “the properties of simple bodies, as well as the forms and properties of compounds of elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent on their atomic weight.”

Currently, D. I. Mendeleev’s Periodic Law has the following formulation: “the properties of chemical elements, as well as the forms and properties of the simple substances and compounds they form, are periodically dependent on the magnitude of the charges of the nuclei of their atoms.”

The peculiarity of the Periodic Law among other fundamental laws is that it does not have an expression in the form of a mathematical equation. The graphic (tabular) expression of the law is the Periodic Table of Elements developed by Mendeleev.

The periodic law is universal for the Universe: as the famous Russian chemist N.D. Zelinsky figuratively noted, the periodic law was “the discovery of the mutual connection of all atoms in the universe.”

In its current state, the Periodic Table of Elements consists of 10 horizontal rows (periods) and 8 vertical columns (groups). The first three rows form three small periods. Subsequent periods include two rows. In addition, starting from the sixth, the periods include additional series of lanthanides (sixth period) and actinides (seventh period).

Over the period, a weakening of metallic properties and an increase in non-metallic properties are observed. The final element of the period is a noble gas. Each subsequent period begins with an alkali metal, i.e., as the atomic mass of the elements increases, the change in chemical properties has a periodic character.

With the development of atomic physics and quantum chemistry, the Periodic Law received a strict theoretical justification. Thanks to the classic works of J. Rydberg (1897), A. Van den Broek (1911), G. Moseley (1913), the physical meaning of the serial (atomic) number of an element was revealed. Later, a quantum mechanical model was created for the periodic change in the electronic structure of atoms of chemical elements as the charges of their nuclei increase (N. Bohr, W. Pauli, E. Schrödinger, W. Heisenberg, etc.).

Periodic properties of chemical elements

In principle, the properties of a chemical element combine all, without exception, its characteristics in the state of free atoms or ions, hydrated or solvated, in the state of a simple substance, as well as the forms and properties of the numerous compounds it forms. But usually the properties of a chemical element mean, firstly, the properties of its free atoms and, secondly, the properties of a simple substance. Most of these properties exhibit a clear periodic dependence on the atomic numbers of chemical elements. Among these properties, the most important, and of particular importance in explaining or predicting the chemical behavior of elements and the compounds they form, are:

Ionization energy of atoms;

Electron affinity energy of atoms;

Electronegativity;

Atomic (and ionic) radii;

Energy of atomization of simple substances

Oxidation states;

Oxidation potentials of simple substances.

The physical meaning of the periodic law is that the periodic change in the properties of elements is in full accordance with the similar electronic structures of atoms periodically renewed at increasingly higher energy levels. With their regular change, the physical and chemical properties naturally change.

The physical meaning of the periodic law became clear after the creation of the theory of atomic structure.

So, the physical meaning of the periodic law is that the periodic change in the properties of elements is in full accordance with the similar electronic structures of atoms periodically renewed at ever higher energy levels. With their regular change, the physical and chemical properties of the elements naturally change.

What is the physical meaning of the periodic law.

These conclusions reveal the physical meaning of D.I. Mendeleev’s periodic law, which remained unclear for half a century after the discovery of this law.

It follows that the physical meaning of D.I. Mendeleev’s periodic law consists in the periodic repetition of similar electronic configurations with an increase in the principal quantum number and the unification of elements according to the proximity of their electronic structure.

The theory of atomic structure has shown that the physical meaning of the periodic law is that with a successive increase in nuclear charges, similar valence electronic structures of atoms are periodically repeated.

From all of the above, it is clear that the theory of atomic structure revealed the physical meaning of D.I. Mendeleev’s periodic law and even more clearly revealed its significance as the basis for the further development of chemistry, physics and a number of other sciences.

Replacing the atomic mass with the charge of the nucleus was the first step in revealing the physical meaning of the periodic law. Further, it was important to establish the reasons for the occurrence of periodicity, the nature of the periodic function of the dependence of properties on the charge of the nucleus, explain the values ​​of the periods, the number of rare earth elements, etc.

For analogue elements, the same number of electrons is observed in shells of the same name at different values ​​of the principal quantum number. Therefore, the physical meaning of the Periodic Law lies in the periodic change in the properties of elements as a result of periodically renewed similar electron shells of atoms with a consistent increase in the values ​​of the principal quantum number.

For analogue elements, the same number of electrons is observed in the orbitals of the same name at different values ​​of the principal quantum number. Therefore, the physical meaning of the Periodic Law lies in the periodic change in the properties of elements as a result of periodically renewed similar electron shells of atoms with a consistent increase in the values ​​of the principal quantum number.

Thus, with a consistent increase in the charges of atomic nuclei, the configuration of the electron shells periodically repeats and, as a consequence, the chemical properties of the elements periodically repeat. This is the physical meaning of the periodic law.

The periodic law of D.I. Mendeleev is the basis of modern chemistry. The study of the structure of atoms reveals the physical meaning of the periodic law and explains the patterns of changes in the properties of elements in periods and in groups of the periodic system. Knowledge of the structure of atoms is necessary to understand the reasons for the formation of a chemical bond. The nature of the chemical bond in molecules determines the properties of substances. Therefore, this section is one of the most important sections of general chemistry.

natural history periodic ecosystem

The main law governing the world of chemical elements was discovered by the great Russian scientist Dmitry Ivanovich Mendeleev.

At the time of this discovery, 63 chemical elements were known. A huge amount of information has accumulated about their properties. However, the abundance of facts that were not understood from a single point of view was a source of difficulties and confusion in chemistry. The brilliant Russian chemist, having discovered the law that governs the properties of elements, as well as the structure of atoms, resolved these difficulties.

Carefully studying and comparing the properties of chemical elements, he sought to uncover the secrets of their distant and close relationships.

Mendeleev describes his searches as follows: “... the thought involuntarily arises that there must necessarily be a connection between the mass and the chemical characteristics of the elements... It is impossible to look for anything - at least mushrooms or some kind of dependence - except looking and trying. So I began to select, writing on separate cards elements with their atomic weights and fundamental properties, similar elements and similar atomic weights, which quickly led to the conclusion that the properties of elements are periodically dependent on their atomic weight...”
By arranging the elements in order of increasing atomic weights, the scientist obtained rows of elements; in each of the rows, the properties of the elements are periodically repeated.

According to Mendeleev’s own definition, the periodic law he discovered is that “the properties of the elements (and, consequently, the simple and complex bodies formed by them) are periodically dependent on their atomic weights.”

Mendeleev showed great insight in discovering periodicity in the world of elements, at a time when many elements had not yet been discovered, and the atomic weights of some of the known elements were determined incorrectly. But proving the existence of this pattern irrefutably turned out to be extremely difficult.

When Mendeleev in his research proceeded from the atomic weights found in the works of that time, the periodicity was often violated.

But the scientist was not at a dead end. He was firmly convinced of the existence of a periodic dependence of the properties of elements on their atomic weights. And when he observed violations of periodicity, only one conclusion was possible for him - obviously, the data that science had was incorrect or incomplete. He corrected the atomic weights of some elements based on theoretical calculations. This was the case with indium, platinum metals, uranium and other elements; later, more accurate measurements of their weights confirmed the correctness of these corrections.

In 1869, having published his work “Relationship of properties with the atomic weight of elements” in the journal of the Russian Chemical Society, Mendeleev introduced the scientific world to the periodic law he discovered. A table of the periodic table of elements was attached to the article. Explaining the essence of the open law, the great scientist also pointed to the existence of elements still unknown to science.

In the periodic table, chemical elements are arranged in increasing order of their atomic weight.

Mendeleev left many places in his system for elements that had not yet been discovered, the approximate atomic weight and other properties of which the scientist calculated, taking into account the nature of neighboring elements. For the first time in the history of chemistry, Mendeleev predicted the existence of unknown elements. He wrote that there must also be elements which he called eka-aluminum, eka-boron and e-silicon.

A number of scientists reacted to the prediction of the Russian scientist with great distrust.

But in August 1875, the French scientist Lecoq de Bois-baudran, through spectral analysis, discovered a new element in zinc blende, which he named gallium (Gallia is the ancient name of France).

In 1879, the famous Swedish chemist Nilsson discovered the second of the elements predicted by Mendeleev. The properties of scandium, as Nilsson named the new element, completely coincided with the properties of ecaboron predicted by Mendeleev. Even the fears of the Russian scientist that the discovery of ecaboron in minerals would be hampered by the presence of another chemical element - yttrium - were justified.

“Thus,” Nilsson concludes his message about the discovery of a new element, “the considerations of the Russian chemist are confirmed, which not only made it possible to predict the existence of the named elements - scandium and gallium, but also to foresee their most important properties in advance.”

Finally, in 1886, the German scientist Winkler discovered the third element predicted by Mendeleev. In his message about this, Winkler pointed out that the new element - germanium - is precisely the e-silicon predicted by Mendeleev.

It was a complete celebration of Mendeleev's discovery.

Friedrich Engels wrote that with the discovery of the periodic law, Mendeleev “performed a scientific feat.”

Mendeleev's discovery was a powerful confirmation of one of the basic laws of dialectics - the law of the transition of quantity into quality.

The properties of chemical elements depend on atomic weights. The law of the transition of quantity into quality, as Friedrich Engels wrote, “is valid... for the chemical elements themselves.”

One of the strengtheners of D. I. Mendeleev’s periodic law was the famous Czech scientist Boguslav Brauner (1855-1935). Brauner confirmed with his work that the place indicated by Mendeleev for the chemical element beryllium in the system is correct. Hence, the atomic weight of this element, calculated by the Russian scientist on the basis of the periodic law, is also correct.

Mendeleev later wrote with gratitude about the work of B. F. Brauner, recalling how often he “had to hear that the question of the atomic weight of beryllium threatens to shake the generality of the periodic law and may require deep transformations in it.”

Based on the law he discovered, Mendeleev corrected the atomic weight of cerium from 92, as was generally accepted, to 138. This caused a stormy protest from some scientists.

“How,” wrote the chemist Rammelsberg, “to correct atomic weights, guided by some kind of table! “Yes, this is pure speculation!” he roared. “This is adjusting facts to some kind of scheme!”
Mendeleev responded to this: “I believe that now it should not, it is impossible to make any precise considerations about the elements, bypassing the law of periodicity.”

Later, Brauner, with his work, confirmed the correctness of the atomic weight of cerium, theoretically derived by Mendeleev. Brauner, and then the English physicist Moseley, pointed out the need to allocate the so-called rare earth elements to a special place.

In 1884, the revolutionary scientist N.A. Morozov, while imprisoned in the Shlisselburg fortress, completed his work there on analyzing the periodic table. He also theoretically predicted the existence of a group of chemical elements - inert gases.

The belonging of an element to a particular period of the periodic table indicates the number of layers in the electron shell of the atom.

Where “noble gases” are now placed in the periodic table - helium, neon, argon and others, Morozov had numbers 4, 20, 40, etc., showing the atomic weights of the missing elements. All these chemical elements were isolated by Morozov into a separate, zero group.

The prediction of Russian scientists was confirmed by the work of English scientists Rayleigh and Ramsey, who discovered inert gases.

The greatness of the Russian genius - Mendeleev is undeniable. But still there were people who tried to take away Mendeleev’s right to be called the author of the periodic law. Mendeleev entered the struggle for Russia's priority in the discovery of the periodic law.

“The affirmation of a law,” he wrote, “is possible only through the derivation of consequences from it, which would be impossible and unexpected without it, and the justification of those consequences in experimental verification. That is why, having seen the periodic law, I, for my part (1869-1871), derived from it such logical consequences that could show whether it was true or not... Without such a method of testing, not a single law of nature can be established. Neither Chancourtois, to whom the French attribute the right to discover the periodic law, nor Newlands, whom the British put forward, nor L. Meyer, who was cited by others as the founder of the periodic law, risked predicting the properties of undiscovered elements, changing the “accepted weights of atoms” and generally calculating the periodic law a new, strictly established law of nature, capable of covering hitherto ungeneralized facts, as I did from the very beginning.”

Anticipating the later discoveries of natural science, the brilliant creator of the periodic law predicted that the atom is indivisible only by chemical means.

Using Mendeleev's law, Russian scientists B. N. Chicherin and N. A. Morozov (their work is discussed below) proposed, based on speculative principles, the first model of the atom, in which it is depicted as a system of bodies reminiscent of the solar system. Later experimental studies and mathematical calculations showed that such a comparison has some basis.

Mendeleev's law is a powerful tool for understanding nature and its laws. All subsequent development of chemistry and physics took place in direct connection with Mendeleev’s law and depending on it. All discoveries in these sciences were illuminated by his law. With the help of this law, the theoretical meaning of the discoveries was shown. At the same time, each such discovery led to clarification and expansion of the law without affecting its fundamental foundations.

Guided by the periodic law, science has determined the structure of the atoms of all elements, which, as established, consist of an electron shell and a nucleus.

The number of electrons increases from one in the hydrogen atom to 101 in the mendeleevium atom, recently discovered and named after the discoverer of the periodic law; this number is in full accordance with the ordinal number of the element in the periodic system. The charge of the nucleus is equal to the sum of the charges of the electrons. The positive charge of the nucleus, balancing the negative electrons, grows from 1 to 101. The positive charge of the nucleus is the main property of the atom, giving it chemical individuality, since the number of electrons depends on the positive charge of the nucleus.

The nucleus also turns out to be complex: it consists of protons and neutrons. This is the bulk of the atom; The mass of the electron is not taken into account, since it is 1836.5 times less than the mass of the proton.

All atoms have the same electrons, but they are located around the nucleus in different layers. The number of these layers reveals the deepest meaning of the periods into which all elements in the Mendeleev system are divided. Each period differs from the other by the presence of an extra electron layer in the atoms of its elements.

The chemical properties of the atom depend on the structure of the electron shell, since chemical reactions are associated with the exchange of external electrons. In addition, a number of physical properties - electrical and thermal conductivity, as well as optical properties are also associated with electrons.

Modern science is increasingly revealing the meaning of Mendeleev’s brilliant creation.

The periodic law indicated the similarity of the chemical properties of elements located in the same group, that is, in the same vertical column of the table.

Now this is perfectly explained by the structure of the electron shell of the atom. Elements of the same group have the same number of electrons in the outer layer: elements of the first group - lithium, sodium, potassium and others - have one electron each in the outer layer; elements of the second group - beryllium, magnesium, calcium and others - two electrons each; elements of the third group - three each, and, finally, elements of the zero group: helium - two, neon, krypton and others - eight electrons each. This is the maximum possible number of electrons in the outer layer and provides these atoms with complete inertness: under normal conditions they do not enter into chemical compounds.

Modern science has shown that the weight of atoms of the same element may not be the same - this depends on the different number of neutrons in the atomic nucleus of a given chemical element. Therefore, in a single cell of the periodic table there is not one type of atom, but several. Such atoms are called isotopes (translated from Greek, “isotope” means “occupying the same place”). The chemical element tin consists, for example, of 12 varieties, extremely similar in properties, but with different atomic weights: the average atomic weight of tin is 118.7.

Almost all elements have isotopes.

So far, 300 natural isotopes have been discovered, about 800 have been artificially obtained. But all of them are naturally located in 101 cells of the periodic table.

All these discoveries, brought to life by Mendeleev's law, emphasize the genius of the Russian scientist, who discovered the fundamental law of inanimate nature, which, however, also has enormous significance for the organic world.

Artificial production of new chemical elements that do not exist in nature.

Scientists now use the Mendeleev system both when splitting atoms and when creating new elements.

This atomic law is guided by chemists, physicists, geologists, agronomists, builders, mechanics, electricians, and astronomers.

The spectroscope showed that elements that exist on Earth also exist on other planets. The chemical transformations that occur here can also occur in other parts of the universe.

Modern science has invaded the depths of the atom. A new science was born - nuclear physics. By influencing the atomic nucleus, scientists now transform some elements into others, synthesizing elements that are not currently found in the earth’s crust. New, artificially created elements include a group of sauranium chemical elements. Modern science has opened the way to the use of intranuclear energy. All these discoveries are inextricably linked with Mendeleev's law.