Discovery of the Periodic Law by D. Mendeleev. Prerequisites for the discovery of the periodic law and the creation of the periodic system of D.I. Mendeleev

There are discoveries in the history of world science that can safely be called revolutionary. There are not so many of them, but they were the ones who brought science to new frontiers, they were the ones who showed a fundamentally new approach to solving problems, they were the ones who had enormous ideological and methodological significance, revealing the scientific picture of the world more deeply and fully. These include, for example, the theory of the origin of species by Charles Darwin, the laws of heredity by G. Mendel, and the theory of relativity by A. Einstein. The periodic law of D.I. Mendeleev is one of such discoveries.

In the history of world science and culture, the name of D.I. Mendeleev occupies one of the most honorable places among the greatest luminaries of thought of all times and peoples. He was not only a brilliant and versatile scientist, who left to his descendants thorough and original works on physics, chemistry, meteorology, metrology, technology, various branches of industry and agriculture, economics, but also an outstanding teacher, a progressive public figure, who devoted his entire life to tireless work on the good and prosperity of their homeland and science.

Any of his works, be it a classic course on Fundamentals of Chemistry, research on the theory of solutions or the elasticity of gases, etc., could not only make the name of the scientist known to his contemporaries, but also leave a significant mark in the history of science. But still, the first thing we think about when talking about D.I. Mendeleev is the periodic law he discovered and the table of chemical elements he compiled. The amazing, familiar clarity of the periodic table from the school textbook of our days hides from us the scientist’s gigantic work in understanding everything that was discovered before him about the transformations of substances, work that only a genius could do, thanks to which a discovery appeared that has no equal in the history of science , which became not only the crown of atomic-molecular science, but also turned out to be a broad generalization of all the factual material of chemistry accumulated over a number of centuries. Therefore, the periodic law became a solid basis for all further development of chemistry and other natural sciences.

We can say that D.I. Mendeleev begins the path to this discovery with his first works, for example, Isomorphism and Specific Volumes, in which, when studying the relationship between properties and composition, he begins to analyze first the properties of individual elements, then natural groups and all classes of compounds, including simple ones substances. But he comes closest to this problem when creating his textbook Fundamentals of Chemistry. The fact is that among the available textbooks in Russian and foreign languages, not a single one satisfied him completely. After the International Congress in Karlsruhe, a chemistry textbook was required, based on new principles accepted by the majority of chemists and reflecting all the latest achievements of chemical theory and practice. In the process of preparing the second part of the Fundamentals of Chemistry, a discovery was made that had no equal in the history of science. Over the next two years, D.I. Mendeleev was busy with important theoretical and experimental research related to clarifying a number of questions that arose in connection with this discovery. The result of this work was the article Periodic Law of Chemical Elements, published in 1871. in Annals of Chemistry and Pharmacy. In it, all aspects of the law he discovered were developed and consistently presented, as well as its most important applications, i.e. D.I. Mendeleev pointed out the path of directed search in the chemistry of the future. After D.I. Mendeleev, chemists knew where and how to look for the unknown. Many remarkable scientists, based on the periodic law, predicted and described unknown chemical elements and their properties. Everything predicted, new unknown elements and their properties and the properties of their compounds, the laws of their behavior in nature - everything was found, everything was confirmed. The history of science knows no other such triumph. Open new law nature. Instead of disparate, unrelated substances, science faced a single, harmonious system that united all the elements of the Universe into one whole.

But the scientific legacy left by D.I. Mendeleev was not only about the discovery of something new. He set an even more ambitious task for science: to explain the mutual relationship between all elements, between their physical and chemical properties. After the discovery of the periodic law, it became clear that the atoms of all elements are built according to a single plan, that their structure can only be such as determines their periodicity chemical properties. D.I. Mendeleev’s law had a huge and decisive influence on the development of knowledge about the structure of the atom and the nature of substances. In turn, the successes of atomic physics, the emergence of new research methods, and the development of quantum mechanics have expanded and deepened the essence of the periodic law and have retained its relevance today.

I would like to quote the words of D.I. Mendeleev, which he wrote down in his diary on July 10, 1905: Apparently, the periodic law does not face the future with destruction, but only promises superstructures and development (Yu. Solovyov. History of Chemistry).

Chemistry, like no other science, has acquired last centuries weight and importance. The practical application of research findings has deeply affected people's lives. Connected with this today is interest in the history of chemistry, as well as in the life and work of great chemists, among whom, without exaggeration, is Dmitry Ivanovich Mendeleev. He is an example of a true scientist who has achieved significant success in any business he undertakes. One cannot but arouse respect for such character traits of the remarkable Russian scientist as independence of scientific thinking, trust only in the results of experimental research, courage in conclusions even when they conflicted with generally accepted ideas. But one cannot but agree that the periodic law and the compiled system of elements are his most significant work. This topic piqued my interest because research in this area is still very relevant. This can be judged by the recent discovery by Russian and American scientists of the 118th element of D.I. Mendeleev’s periodic table. This scientific event once again emphasizes that, despite more than a century of history, the periodic law remains the basis of scientific research. This work aims not only to talk about the discovery of this great law, about that truly titanic work that preceded this event, but is also an attempt to understand the prerequisites, to analyze the current situation with the classification and systematization of chemical elements before 1869. and, in addition, touch upon recent history doctrine of periodicity.

Prerequisites for the discovery of the periodic law

Any discovery in science, of course, is never sudden and does not arise out of nowhere. This is a complex and lengthy process, to which many, many wonderful scientists contribute. A similar situation has developed with the periodic law. And, in order to more clearly imagine the prerequisites that created the necessary conditions for the discovery and substantiation of the periodic law, we should consider the main directions of research in the field of chemistry by the middle of the 19th century (Appendix Table 1).

It must be said that during the first decades of the 19th century. There was rapid progress in the development of chemistry. Emerging at the very beginning of the century, chemical atomism was a powerful stimulus for the development of theoretical problems and the development of experimental research, which led to the discoveries of basic chemical laws (the law of multiple ratios and the law of constant proportions, the law of volumes of reacting gases, the law of Dulong and Petit, the rule of isomorphism and others ). Experimental research, mainly of a chemical-analytical nature, related to the establishment of the atomic weights of elements, the discovery of new elements and the study of the composition of various chemical compounds, has also received significant development. But difficulties arose in determining atomic weights, mainly due to the fact that the exact formulas of the simplest compounds (oxides), on the basis of which researchers calculated atomic weights, remained unknown. Meanwhile, some regularities that had already been discovered, which could serve as important criteria in establishing the exact values ​​of atomic weights, were used extremely rarely (Gay-Lussac's volumetric law, Avogadro's law). Most chemists considered them random, without a strict factual basis. This lack of confidence in the correctness of the definitions of atomic weights led to the emergence of numerous systems of atomic weights and equivalents and even raised doubts about the need to accept the very concept of atomic weight in chemistry. As a result of such confusion, even relatively simple connections were depicted in the mid-19th century. many formulas, for example, water was represented simultaneously by four formulas, acetic acid by nineteen, etc. But at the same time, many chemists continued to search for new methods for determining atomic weights, as well as new criteria that would at least indirectly confirm the correctness of the values ​​obtained from the analysis of oxides. The concepts of atom, molecule and equivalent proposed by Gerard already existed, but they were used mainly by young chemists. Influential chemists of older generations adhered to the ideas that entered science in the 20s and 30s thanks to Berzelius, Liebig and Dumas. A situation arose when chemists ceased to understand each other. In such a difficult situation, the idea arose to gather the most prominent scientists different countries in order to agree on the unity of ideas according to the most general issues chemistry, in particular - about basic chemical concepts. This International Congress took place in 1860. in Karlsruhe. Among the seven Russian chemists, D.I. Mendeleev also took part in it. The main goal of the congress - to come to unity in the definitions of the fundamental concepts of chemistry - atom, molecule, equivalent - was achieved. The participants of the congress, including D.I. Mendeleev, were especially impressed by the speech of S. Cannizzaro, who outlined the foundations of the atomic-molecular theory. Subsequently, D.I. Mendeleev repeatedly noted the enormous importance of the congress in Karlsruhe for the progress of chemistry in general, and for the genesis of the idea of ​​the periodic law of chemical elements in particular, and S. Cannizzaro considered his predecessor, because the atomic masses he established provided the necessary fulcrum.

The first attempts to systematize the elements known by that time were made in 1789. A. Lavoisier in his chemistry textbook. His Table of Simple Solids included 35 simple substances. And by the time the periodic law was discovered, there were already 63 of them. It must be said that in the first half of the 19th century. scientists proposed various classifications of elements similar in their properties. However, attempts to establish patterns of changes in properties depending on atomic weight were random in nature and were limited for the most part to the statement of individual facts of correct relationships numerical values atomic weights between individual elements in groups of similar elements. For example, the German chemist I. Döbereiner in 1816 - 1829. When comparing the atomic weights of some chemically similar elements, I found that for many elements widespread in nature these numbers are quite close, and for such elements as Fe, Co, Ni, Cr, Mn, they are practically the same. In addition, he noted that the relative atomic weight of SrO is an approximate arithmetic mean of the atomic weights of CaO and BaO. On this basis, Döbereiner proposed the law of triads, which states that elements with similar chemical properties can be combined into groups of three elements (triads), for example Cl, Br, J or Ca, Sr, Ba. In this case, the atomic weight of the middle element of the triad is close to half the sum of the atomic weights of the outer elements.

Simultaneously with Döbereiner, L. Gmelin was working on a similar problem. Thus, in his famous reference guide - Handbuch der anorganischen Chemie, he provided a table of chemically similar elements arranged in groups in in a certain order. But the principle of constructing his table was somewhat different (Appendix Table 2). At the top of the table, outside the groups of elements, three basic elements were located - O, N, H. Below them were triads, tetrads and pentads, and under oxygen there were groups of metalloids (according to Berzelius), i.e. electronegative elements, under hydrogen - metals. The electropositive and electronegative properties of groups of elements decrease from top to bottom. In 1853 Gmelin's table was expanded and improved by I.G. Gledston, who included rare earth and newly discovered elements (Be, Er, Y, Di, etc.). Subsequently, a number of scientists studied the law of triads, for example E. Lenssen. In 1857 he compiled a table of 20 triads and proposed a method for calculating atomic weights based on three triads, or enneads (nines). He was so confident in the absolute accuracy of the law that he even tried to calculate the still unknown atomic weights of some rare earth elements.

Further attempts to establish the relationship between the physical and chemical properties of elements also came down to comparisons of the numerical values ​​of atomic weights. So M.I. Pettenkofer in 1850 noticed that the atomic weights of some elements differ by a multiple of 8. The reason for such comparisons was the discovery of homologous series of organic compounds. It was while trying to establish the existence of similar series for elements that M. Pettenkofer, having made calculations, found that the difference in atomic weights of some elements was 8, sometimes 5 or 18. In 1851. similar considerations about the existence of correct numerical relationships between the values ​​of the atomic weights of elements were expressed by J.B. Dumas.

In the 60s of the XIX century. comparisons of atomic and equivalent weights and chemical properties of elements of a somewhat different kind appeared. Along with comparisons of the properties of elements in groups, the groups of elements themselves began to be compared with each other. Such attempts led to the creation of a variety of tables and graphs that combined all or most of the known elements. The author of the first table was W. Odling. He divided the 57 elements (in the final version) into 17 groups - monads, dyads, triads, tetrads and pentads, without including a number of elements. The meaning of this table was quite simple and did not represent anything fundamentally new. A few years later, more precisely in 1862, the French chemist B. de Chancourtois made an attempt to express the relationships between the atomic weights of elements in geometric shape(Appendix Table 3). He arranged all the elements in increasing order of their atomic weights on the side surface of the cylinder along a helical line running at an angle of 45°. The side surface of the cylinder was divided into 16 parts (the atomic weight of oxygen). The atomic weights of the elements are plotted on the curve on the appropriate scale (the atomic weight of hydrogen is taken as one). If you unfold the cylinder, then on the surface (plane) you will get a series of straight segments parallel to each other. On the first segment from the top there are points for elements with atomic weights from 1 to 16, on the second - from 16 to 32, on the third - from 32 to 48, etc. L.A. Chugaev in his work The Periodic System of Chemical Elements noted that in the de Chancourtois system a periodic alternation of properties clearly appears... It is clear that this system already contains the germ of the periodic law. But the Chancourtois system gives ample scope to arbitrariness. On the one hand, among the analogue elements there are often elements that are completely foreign. So, behind oxygen and sulfur, titanium comes across between S and Te; Mn is among the analogues of Li, Na and K; iron is placed on the same generatrix as Ca, etc. On the other hand, the same system gives two places for carbon: one for C with an atomic weight of 12, the other corresponding to an atomic weight of 44 (N. Figurovsky. Essay on the general history of chemistry). Thus, having fixed some relationships between the atomic weights of elements, Chancourtois was unable to come to the obvious generalization - the establishment of the periodic law.

Almost simultaneously with the de Chancartois helix, the tabular system of J. A. R. Newlands appeared, which he called the law of octaves and has much in common with Odling’s tables (Appendix Table 4). The 62 elements in it are arranged in ascending order of equivalent weights in 8 columns and 7 groups arranged horizontally. It is characteristic that the symbols of elements have numbers instead of atomic weights. There are 56 of them in total. In some cases, there are two elements under the same number. Newlands emphasized that the numbers of chemically similar elements differ from each other by the number 7 (or a multiple of 7), for example, an element with serial number 9 (sodium) repeats the properties of element 2 (lithium), etc. In other words, the same picture is observed as in the musical scale - the eighth note repeats the first. Hence the name of the table. Newlands' law of octaves has been repeatedly analyzed and criticized since various points vision. The frequency of changes in the properties of elements is visible only in a hidden form, and the fact that not a single one is left in the table free space for elements not yet discovered makes this table only a formal comparison of elements and deprives it of the meaning of a system expressing the law of nature. Although, as L.A. Chugaev notes, if Newlands had used instead of equivalents when compiling his table newest values atomic weights, recently established by Gerard and Cannizzaro, he could have avoided many contradictions.

Among other researchers who in the 60s of the 19th century were engaged in comparisons of the atomic weights of elements taking into account their various properties, one can name the German chemist L. Meyer. In 1864 he published the book Modern Theories of Chemistry and Their Implications for Chemical Statics, which contains a table of 44 elements (63 were known at that time), arranged in six columns according to their hydrogen valency. From this table it is clear that Meyer sought, first of all, to establish the correctness of the differences in the values ​​of atomic weights in groups of similar elements. However, he was far from noticing the most significant feature of the internal connection between elements - the periodicity of their properties. Even in 1870, after the appearance of several reports by D.I. Mendeleev about the periodic law, Meyer, who published a curve of periodic changes in atomic volumes, could not see in this curve, which was one of the expressions of the periodic law, the main feature of the law. Meanwhile, a few months after the appearance of D.I. Mendeleev’s first reports about the periodic law he discovered, L. Meyer made a claim to the priority of this discovery and for a number of years persistently expressed claims in this regard.

These, in the most general terms, are the main attempts to establish an internal connection between elements, undertaken before the appearance of D.I. Mendeleev’s first reports on the periodic law.

D.I. Mendeleev hardly mentions how the discovery was made either in his articles on the periodic law or in his autobiographical notes. But when one day, about thirty years after the discovery of the periodic law, one journalist asked him: How did you come up with the periodic system?, D.I. Mendeleev replied: I’ve been thinking about it, maybe for twenty years (N. Figurovsky. D. I. Mendeleev.1834 - 1907). Indeed, it can definitely be said that all of his previous scientific activities led to the discovery of D.I. Mendeleev’s periodic law. The beginning was made already in his first works, devoted to isomorphism and specific volumes. The first elements that stood out among others for their individuality, to which D.I. Mendeleev drew attention, were silicon and carbon. The general formulas of the most important binary compounds of carbon and silicon were identical, but when studying the dependence of the properties of their compounds on the composition, the following differences were revealed: in composition - certain compounds are characteristic of carbon, and undefined ones are characteristic of silicon; in the structure of compounds - the presence of stable radicals and homochains, as well as unsaturated or unsaturated compounds in carbon and heterochains in silicon. This led to significant differences in the properties of most compounds of these two elements. The scientist was interested in what other elements, besides silicon, are capable of forming unspecified compounds. They turned out to be, first of all, boron and phosphorus. Speaking about the ability of different elements to form salts and emphasizing the uncertainty of the composition of many compounds, D.I. Mendeleev noted in 1864: Uncertain compounds are compounds by similarity (solutions, alloys, isomorphic mixtures are formed predominantly by similar bodies), and true chemical compounds are compounds by difference - combinations of bodies with distant properties (M. Mladentsev. D. I. Mendeleev. His life and work).

Based on the study of the crystalline forms of compounds and their relationship with composition, D.I. Mendeleev came to the conclusion that the individual (composition) of a certain compound may be subordinated to the general one (the same crystalline form inherent in several compounds). Indeed, the number of types of crystalline forms is significantly smaller than the number of possible chemical compounds. While studying the phenomenon of isomorphism, D.I. Mendeleev made another conclusion about the relationship between the individual and the general: some compounds of two different elements turned out to be isomorphic. But this isomorphism did not manifest itself for all oxidation stages of the compared compounds, but only for some. In addition, it was noted that the formation of isomorphic mixtures is also possible in the case when the concentration of one of the substances is noticeably lower than the concentration of the other. D.I. Mendeleev also drew attention to the existence of polymer isomorphism and to the series K2O, Na2O, MgO, FeO, Fe2O3, Al2O3, SiO2, where the oxides are ranked according to the degree of enhancement of acidic properties. He accompanied this position with the following comment: When substituting by groups, the sum of the bodies located at the edges is replaced by the sum of the bodies contained between them.

Consideration of these issues led D.I. Mendeleev to search for connections between classes of compounds or their series that have general formulas. He saw the reason for the difference between them in the nature of the elements.

As a result of his research, D.I. Mendeleev concluded that the relationships between the various properties of elements are characterized by the categories of general (single), specific (special) and individual (single). General properties are properties that relate primarily to the concept of element and are united specific characteristics the atom as a whole. D.I. Mendeleev called such properties fundamental, and the first of them he considered the atomic weight (atomic mass) of the element. As for the properties of compounds, they can be generalized within a certain set of compounds, and various criteria can be used as a basis. Such properties are called specific (special), for example, metallic and non-metallic properties of simple substances, acid-base properties of compounds, etc. By individual we mean those unique properties that distinguish two analogous elements or two compounds of the same class, for example, different solubilities of magnesium and calcium sulfates, etc. The lack of necessary data on the internal structure of molecules and atoms forced D.I. Mendeleev to consider such properties as atomic and molecular volumes in his work Specific Volumes. These properties were calculated from the properties of general (atomic and molecular masses) and specific properties of compounds (density of a simple or complex substance). Analyzing the nature of changes in such properties, D.I. Mendeleev emphasized that the patterns of change specific gravity and atomic volumes in the series of elements are disrupted by those changes in the physical and chemical nature of the elements that are associated with the number of atoms included in the molecule and the quality of the atoms or the form of chemical compounds. Thus, although such properties were associated with general properties, they inevitably turned out to be among the specific ones - they reflected objective differences in the nature of the elements. This is an idea of ​​three types of properties, their relationship with each other and ways to find patterns general and individual manifestations later formed the basis of the doctrine of periodicity.

So, summing up all of the above, we can say that by the middle of the 19th century, the question of systematizing accumulated material was one of the main tasks in chemistry, as well as in any other science. Simple and complex substances were studied in accordance with the classifications accepted in science at that time: firstly, by physical properties, and secondly, by chemical properties. Sooner or later it was necessary to try to link both classifications together. Many such attempts were made even before D.I. Mendeleev. But scientists who tried to discover any numerical patterns when comparing the atomic weights of elements ignored the chemical properties and other connections between elements. As a result, not only were they unable to arrive at a periodic law, but they were not even able to eliminate the inconsistencies in comparisons. Indeed, the listed attempts by Odling, Newlands, Chancourtois, Meyer and other authors are only hypothetical schemes containing only a hint of the presence of internal relationships between the properties of elements, devoid of signs of a scientific theory and, especially, a law of nature. The shortcomings that existed in all these constructions raised doubts about the correctness of the idea of ​​​​the existence of a universal connection between elements, even among the authors themselves. However, D.I. Mendeleev notes in the Fundamentals of Chemistry that some germs of the periodic law are visible in the constructions of de Chancourtois and Newlands. The task of developing a classification of elements based on the entire set of information about the composition, properties, and sometimes the structure of compounds fell to D.I. Mendeleev. The study of the relationship between properties and composition forced him to analyze first the properties of individual elements (manifested in the study of isomorphism, specific volumes, and a comparison of the properties of carbon and silicon), then natural groups (atomic masses and chemical properties) and all classes of compounds (the totality of physical and chemical properties) , including simple substances. And the impetus for this kind of search was the work of Dumas. Thus, we can rightfully claim that in his work D.I. Mendeleev had no co-authors, but only predecessors. And unlike his predecessors, D.I. Mendeleev did not look for specific laws, but sought to solve a general problem of a fundamental nature. At the same time, again, unlike his predecessors, he operated with verified quantitative data, and personally experimentally tested the dubious characteristics of the elements.

Discovery of the periodic law

The discovery of the periodic law of chemical elements is not a common phenomenon in the history of science, but, perhaps, exceptional. It is natural, therefore, that interest is aroused both by the emergence of the very idea of ​​the periodicity of the properties of chemical elements, and by the creative process of developing this idea, its embodiment into a comprehensive law of nature. At present, based on D.I. Mendeleev’s own evidence, as well as on published materials and documents, it is possible to restore with sufficient reliability and completeness the main stages of D.I. Mendeleev’s creative activity related to the development of the system of elements.

In 1867 Dmitry Ivanovich was appointed professor of chemistry at St. Petersburg University. Having thus occupied the department of chemistry at the capital’s university, i.e. Having essentially become the leader of university chemists in Russia, Mendeleev took all measures within his power to significantly improve the teaching of chemistry at St. Petersburg and other Russian universities. The most important and urgent task that arose before Dmitry Ivanovich in this direction was the creation of a chemistry textbook that reflected the most important achievements of chemistry of that time. Both the textbook by G.I. Hess and the various translated publications that the students used were very outdated and, naturally, could not satisfy D.I. Mendeleev. That's why he decided to write a completely new course, compiled according to his own plan. The course was entitled Fundamentals of Chemistry. By the beginning of 1869 work on the second edition of the first part of the textbook, dedicated to the chemistry of carbon and halogens, had come to an end and Dmitry Ivanovich intended to continue work on the second part without delay. Thinking over the plan for the second part, D.I. Mendeleev drew attention to the fact that the order of arrangement of material about elements and their compounds in existing chemistry textbooks is largely random and does not reflect the relationships not only between groups of chemically dissimilar elements, but even between individual similar elements. Reflecting on the question of the sequence of consideration of groups of chemically dissimilar elements, he came to the conclusion that there must be some kind of scientifically based principle that should be used as the basis for the plan of the second part of the course. In search of such a principle, D.I. Mendeleev decided to compare groups of chemically similar elements in order to discover the desired pattern. After several unsuccessful attempts he wrote on cards the symbols of the elements known at that time and wrote down their basic physical and chemical properties next to them. By combining the distribution of these cards, D.I. Mendeleev discovered that if all known elements are arranged in increasing order of their atomic masses, then it is possible to identify groups of chemically similar elements by dividing the entire series into periods and placing them under each other, without changing the order of the elements . So March 1, 1869 The first table, a system of elements, was compiled, first fragmentarily, and then completely. This is how D.I. Mendeleev himself later talked about it. I was repeatedly asked: on what basis, based on what thought did I find and defend the periodic law? I will give a feasible answer here. ... Having devoted my energies to the study of matter, I see in it two such signs or properties: mass, occupying space and manifested in attraction, and most clearly or most realistically in weight, and individuality, expressed in chemical transformations, and most clearly formulated in ideas about chemical elements. When thinking about matter, in addition to any idea of ​​material atoms, it is impossible for me to avoid two questions: how much and what kind of substance is given, to which the concepts of mass and chemistry correspond. The history of science concerning matter, i.e. chemistry, leads, willy-nilly, to the demand for recognition not only of the eternity of the mass of matter, but also of the eternity of chemical elements. Therefore, the thought involuntarily arises that there must be a connection between the mass and the chemical properties of the elements, and since the mass of a substance, although not absolute, but only relative, is expressed finally in the form of atoms, then it is necessary to look for a functional correspondence between the individual properties of the elements and their atomic weights. To look for something... there is no other way than 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, and, doubting many ambiguities, I did not doubt for a minute the generality of the conclusion drawn, since it was impossible to allow chance (N. Figurovsky. Dmitry Ivanovich Mendeleev).

The scientist entitled the resulting table Experience of a system of elements based on their atomic weight and chemical similarity. He immediately saw that this table not only provided the basis for the logical plan of the second part of the course on Fundamentals of Chemistry, but, above all, expressed the most important law of nature. A few days later, the printed table (with Russian and French titles) was sent to many prominent Russian and foreign chemists. D.I. Mendeleev sets out the main provisions of his discovery, arguments in favor of the conclusions and generalizations he made in the article Correlation of properties with the atomic weight of elements. This work begins with a discussion of the principles of classification of elements. Scientist gives historical overview attempts at classification in the 19th century and comes to the conclusion that at present there is not a single general principle , withstands criticism, can serve as a support for judging the relative properties of elements and allows them to be arranged in a more or less strict system. Only regarding some groups of elements there is no doubt that they form one whole, represent a natural series of similar manifestations of matter (M. Mladentsev. D. I. Mendeleev. His life and work). Further, Dmitry Ivanovich explains the reasons that prompted him to study the relationships between elements by the fact that having undertaken to compile a guide to chemistry, called the Fundamentals of Chemistry, he had to settle on some system of simple bodies, so that in their distribution he would not be guided by random, as if instinctive motives, but some definite beginning. This is the exact beginning, i.e. the principle of the system of elements, according to the conclusion of D.I. Mendeleev, should be based on the value of the atomic weights of the elements. Then comparing the elements with the lowest atomic weights, Mendeleev builds the first fundamental fragment of the periodic system (Appendix Table 8). He states that for elements with large atomic weights similar relationships are observed. This fact makes it possible to formulate the most important conclusion that the magnitude of the atomic weight determines the nature of the element as much as the weight of the particle determines the properties and many reactions of a complex body. After discussing the question of the possible relative arrangement of all known elements, D.I. Mendeleev gives his table Experience of a system of elements.... The article ends with brief conclusions that have become the main provisions of the periodic law: Elements arranged according to the magnitude of their atomic weight represent a clear periodicity of properties... The comparison of elements or groups according to the magnitude of the atomic weight corresponds to their so-called atomicity and to some extent the difference in chemical character... One should expect more discoveries many unknown simple bodies, for example, elements similar to Al and Si with a share of 65 - 75... The value of the atomic weight of an element can sometimes be corrected by knowing its analogies. So, Te's share should not be 128, but 123 - 126? (N. Figurovsky. Dmitry Ivanovich Mendeleev). Thus, the article Correlation of properties with the atomic weight of elements clearly and distinctly reflects the sequence of D.I. Mendeleev’s conclusions that led to the creation of the periodic table of elements, and the conclusions indicate how correctly the scientist assessed the importance of his discovery from the very beginning. The article was sent to the Journal of the Russian Chemical Society and appeared in print in May 1869. In addition, it was intended for a report at the next meeting of the Russian Chemical Society, which took place on March 18. Since D.I. Mendeleev was absent at that time, the Secretary of the Chemical Society N.A. Menshutkin spoke on his behalf. In the minutes of the society there remains a dry record about this meeting: N. Menshutkin reports on behalf of D. Mendeleev the experience of a system of elements based on their atomic weight and chemical similarity. Due to the absence of D. Mendeleev, the discussion of this message was postponed until the next meeting (Children's Encyclopedia). Scientists, contemporaries of D.I. Mendeleev, who first heard about this periodic system of elements, remained indifferent to it and could not immediately understand the new law of nature, which subsequently turned the entire course of development of scientific thought upside down.

So, it would seem that the initially posed task - to find the exact beginning, the principle of rational distribution of material in the second part of the Fundamentals of Chemistry - was solved, and D.I. Mendeleev could continue to work on the course. But now the scientist’s attention was completely captured by the system of elements and the new ideas and questions that arose, the development of which seemed to him more significant and important than writing a textbook on chemistry. Seeing a law of nature in the created system, Dmitry Ivanovich completely switched to research related to some ambiguities and contradictions in the pattern he found.

This intense work continued for almost two years, from 1869. to 1871 The result of the research was such publications by D.I. Mendeleev as about the atomic volumes of elements (it is said that the atomic volumes of simple substances are a periodic function of atomic masses); about the amount of oxygen in hydrochloric oxides (it has been shown that the highest valence of an element in a salt-forming oxide is a periodic function of the atomic mass); about the place of cerium in the system of elements (it is proved that the atomic weight of cerium, equal to 92, is not correct and should be increased to 138, and a new version of the system of elements is also given). Of the subsequent articles, two were of greatest importance for the development of the main provisions of the periodic law - Natural system elements and its application to indicating the properties of undiscovered elements, published in Russian, and Periodic Law for Chemical Elements, printed in German. They contain not only all the data on the periodic law collected and obtained by D.I. Mendeleev, but also different ideas and findings not yet published. Both articles seem to complete the enormous research work done by the scientist. It was in these articles that the periodic law received its final design and formulation.

At the beginning of the first article, D.I. Mendeleev states that certain facts previously did not fit into the framework of the periodic system. Thus, some of the elements, namely the cerite elements, uranium and indium, did not find an appropriate place in this system. But ... at the present time, - D.I. Mendeleev further writes, - such deviations from periodic legality ... can already be eliminated with much greater completeness than was possible in the past (N. Figurovsky. Dmitry Ivanovich Mendeleev). He justifies his proposed places in the system for uranium, cerite metals, indium, etc. The central position in the article is occupied by a table of the periodic system in a more advanced form compared to the first options. Dmitry Ivanovich also proposes a new name - Natural System of Elements, thereby emphasizing that the periodic system represents a natural arrangement of elements and is in no way artificial. The system is based on the distribution of elements according to their atomic weight, and periodicity is immediately noticeable. Based on this, seven groups or seven families are compiled for the elements, which are indicated in the table with Roman numerals. In addition, some elements in the periods beginning with potassium and rubidium are assigned to the eighth group. Further, D.I. Mendeleev characterizes individual patterns in the periodic system, pointing out the presence of large periods in it, the differences in the properties of elements of the same group belonging to even and odd series. As one of the important characteristics of the system, Dmitry Ivanovich takes the higher oxides of elements and enters into the table the types of oxide formulas for each group of elements. Here we also discuss the question of typical formulas of other compounds of elements, the properties of these compounds in connection with the justification of the place of individual elements in the periodic table. After comparing some physical and chemical characteristics of elements, D.I. Mendeleev raises the question of the possibility of predicting the properties of chemical elements that have not yet been discovered. He points out that in the periodic table the presence of a number of cells not occupied by known elements is striking. This applies, first of all, to empty cells in the third and fourth groups of analogue elements - boron, aluminum and silicon. D.I. Mendeleev makes a bold assumption about the existence in nature of elements that should, in the future, when they are discovered, occupy empty cells in the table. He offers not only conventional names (ekaboron, ekaaluminum, ekasilicon), but also, based on their position in the periodic table, describes what physical and chemical properties these elements should have. The work also discusses the possibility of the existence of elements that can fill other empty cells in the table. And, as if to sum up what has been said, D.I. Mendeleev writes that the application of the proposed system of elements to the comparison of both themselves and the compounds formed by them represents such benefits that none of the points of view has provided until now pores used in chemistry.

The second extensive work - On the Law of Periodicity - was conceived by the scientist in 1871. It was in it that it was intended to give a complete and substantiated presentation of the discovery in order to introduce it to wide circles of the world scientific community. The main part of this work was the article Periodic Law of Chemical Elements, published in the Annals of Chemistry and Pharmacy. The article was the result of more than two years of work by the scientist. After the introductory part, in which some important definitions are given and, above all, the definition of the concepts element and simple body, as well as some general considerations about the properties of elements and compounds and the possibilities of their comparisons and generalizations, D.I. Mendeleev considers the most important provisions of the periodic law and conclusions from it in connection with our own research. Thus, in the Essence of the Law of Periodicity, based on comparisons of the atomic weights of elements, the formulas of their oxides and oxide hydrates, Dmitry Ivanovich states that there is a close natural relationship between the atomic weights and all other properties of the elements. A common feature of a regular change in the properties of elements arranged in increasing order of their atomic weights is the periodicity of the properties. He writes that as the atomic weight increases, the elements first have more and more changeable properties, and then these properties are repeated again in a new order, in a new row and in a series of elements and in the same sequence as in the previous row. Therefore, the law of periodicity can be formulated as follows: the properties of elements, and therefore the properties of the simple and complex bodies they form, are periodically dependent (i.e., they repeat correctly) on their atomic weight. Further, the stated fundamental position is illustrated by a large number of examples of periodic changes in the properties of both elements and the compounds they form. The second paragraph, Application of the law of periodicity to the systematics of elements, begins with the words that the system of elements has not only pedagogical significance, not only facilitates the study of various facts, bringing them into order and connection, but also has a purely scientific significance, revealing analogies and thereby pointing out new ones ways to study the elements. It lists methods for calculating the atomic weights of elements and the properties of their compounds based on the position of the elements in the periodic table (beryllium, vanadium, thallium), in particular the method of proportions. Application of the Law of Periodicity to the Determination of Atomic Weights of Little-Studied Elements discusses the position of some elements in the periodic table and describes a method for calculating atomic weights based on a system of elements. The fact is that by the time the periodic law was discovered, the atomic weights of a number of elements were, as D.I. Mendeleev puts it, established on sometimes very shaky criteria. Therefore, some elements, when placed in the periodic table only according to the atomic weight accepted at that time, were clearly out of place. Based on a consideration of the complex of physical and chemical properties of such elements, D.I. Mendeleev proposed a place in the system corresponding to their properties, and in a number of cases it was necessary to revise their hitherto accepted atomic weight. Thus, indium, the atomic weight of which was taken to be 75 and which, on this basis, should have been placed in the second group, the scientist transferred to the third group, while correcting the atomic weight to 113. For uranium with an atomic weight of 120 and position in the third group, based on detailed analysis of the physical and chemical properties and properties of its compounds, a place in the sixth group was proposed, and the atomic weight was doubled (240). Next, the author considered a very difficult, especially at that time, question of the placement of rare earth elements in the periodic table - cerium, didymium, lanthanum, yttrium, erbium. But this issue was resolved only after more than thirty years. This work ends with the application of the law of periodicity to the determination of the properties of elements not yet discovered, which is perhaps especially important for confirming the periodic law. Here D.I. Mendeleev points out that in some places the table is clearly missing several elements that should be discovered in the future. He predicts the properties of not yet discovered elements, primarily analogues of boron, aluminum and silicon (eca-boron, eka-aluminum, eca-silicon). These predictions of the properties of still unknown elements characterize not only the scientific courage of the brilliant scientist, based on firm confidence in the law he discovered, but also the power of scientific foresight. A few years later, after the discovery of gallium, scandium and germanium, when all his predictions were brilliantly confirmed, the periodic law was recognized throughout the world. In the meantime, in the first years after the publication of the article, these predictions went almost unnoticed by the scientific world. In addition, the article raised the issue of correcting the atomic weights of some elements based on the periodic law and applying the periodic law to obtain additional data on the forms of chemical compounds of elements.

So, by the end of 1871. all the main provisions of the periodic law and very bold conclusions from it made by D.I. Mendeleev were published in a systematic presentation. This article completed the first and most important stage of D.I. Mendeleev’s research on the periodic law; it became the fruit of more than two years of titanic work on solving various problems that arose before the scientist after he compiled the first table of the Experience of a system of elements in March 1869. In subsequent years, Dmitry Ivanovich, from time to time, returned to the development and discussion of individual problems associated with the further development of the periodic law, but he was no longer engaged in long-term systematic research in this area, as was the case in 1869 - 1871. This is how D.I. Mendeleev himself assessed his work in the late 90s: This is the best summary of my views and thoughts on the periodicity of elements and the original, according to which so much was later written about this system. This is the main reason for my scientific fame, because much was justified much later (R. Dobrotin. Chronicle of the life and work of D. I. Mendeleev). The article develops and consistently presents all aspects of the law he discovered, and also formulates its most important applications. Here D.I. Mendeleev gives a refined, now canonical formulation of the periodic law: ... the properties of elements (and, consequently, simple and complex bodies formed from them) are periodically dependent on their atomic weight (R. Dobrotin. Chronicle of life and activity of D. I. Mendeleev). In the same article, the scientist also gives a criterion for the fundamental nature of the laws of nature in general: Each law of nature receives scientific significance only if it, so to speak, allows practical consequences, i.e. those logical conclusions that explain the unexplained and point to hitherto unknown phenomena, and especially if the law leads to predictions that can be verified by experience. In the latter case, the significance of the law is obvious and it is possible to verify its validity, which, at least, encourages the development of new areas of science (R. Dobrotin. Chronicle of the life and work of D. I. Mendeleev). Applying this thesis to the periodic law, Dmitry Ivanovich names the following possibilities for its application: to a system of elements; to determine the properties of still unknown elements; to determine the atomic weight of little-studied elements; to correct the values ​​of atomic weights; to replenish information about the forms of chemical compounds. In addition, D.I. Mendeleev points out the possibility of applicability of the periodic law: to the correct understanding of the so-called molecular compounds; to determine cases of polymerization among inorganic compounds; to comparative study physical properties simple and complex bodies (R. Dobrotin. Chronicle of the life and work of D. I. Mendeleev). We can say that in this article the scientist outlined a broad research program on inorganic chemistry, based on the doctrine of periodicity. Indeed, many important areas of inorganic chemistry at the end of the 19th and beginning of the 20th centuries actually developed along the paths outlined by the great Russian scientist D.I. Mendeleev, and the discovery and subsequent recognition of the periodic law can be considered as the completion and generalization of an entire period in the development of chemistry.

Triumph of the periodic law

Like any other great discovery, such a major scientific generalization as the periodic law, which also had deep historical roots, should have evoked responses, criticism, recognition or non-recognition, and applications in research. But oddly enough, in the first years after the discovery of the law, there were virtually no responses or speeches from chemists assessing it. In any case, in the early 70s there were no serious responses to D.I. Mendeleev’s articles. Chemists preferred to remain silent, of course, not because they had not heard anything about this law or did not understand it, but, as E. Rutherford later explained this attitude, the chemists of his time were simply more busy collecting and obtaining facts than thinking about their relationships. However, D.I. Mendeleev’s speeches did not go completely unnoticed, although they caused an unexpected reaction from some foreign scientists. But all the publications that appeared in foreign journals did not concern the essence of D.I. Mendeleev’s discovery, but raised the question of the priority of this discovery. The great Russian scientist had many predecessors who tried to approach the issue of systematizing the elements and, therefore, when D.I. Mendeleev showed that the periodic law is a fundamental law of nature, some of them laid claim to priority in the discovery of this law. Thus, the correspondent of the German Chemical Society in London, R. Gerstel, wrote a note in which he argued that D.I. Mendeleev’s idea about the natural system of elements was expressed several years before him by W. Odling. Somewhat earlier, a book by the German chemist H.V. Blomstrand appeared, in which he proposed a classification of elements according to their analogy with hydrogen and oxygen. All elements were divided by the author into two large groups based on electrical polarity in the spirit of the electrochemical theory of I.Ya. Berzelius. The principles of the periodic table were also presented with significant distortions in G. Baumgauer’s brochure. But most of the publications were devoted to L. Meyer’s system of elements, entirely based on the principles of natural taxonomy of D. M. Mendeleev, which, as he claimed, was published back in 1864. L. Meyer was a major representative of inorganic chemistry in Germany in the 60s - 80s of the 19th century. All his works were devoted mainly to the study of the physicochemical properties of elements: atomic masses, heat capacity, atomic volumes, valence, isomorphism and various methods for their determination. He saw the main goal of his research in collecting accurate experimental data (clarifying atomic masses, establishing physical constants) and did not set himself broad tasks of generalizing the accumulated material, unlike D.I. Mendeleev, who, when studying various physical and chemical properties, tried to find the relationship between all elements, find out the nature of changes in the properties of elements. These speeches, in essence, limited the initial reaction of the scientific world to the discovery of the periodic law and to the main articles on the periodic law published by D.I. Mendeleev in 1869 - 1871. Basically, they were aimed at questioning the novelty and priority of the discovery and at the same time using the basic idea of ​​D.I. Mendeleev for their own constructions of systems of elements.

But only four years passed, and the whole world started talking about the periodic law as a most brilliant discovery, about the justification of the brilliant predictions of D.I. Mendeleev. Dmitry Ivanovich, from the very beginning completely confident in the special scientific importance of the law he discovered, could not even imagine that within a few years he would witness the scientific triumph of his discovery. Back in February 1874 French chemist P. Lecoq de Boisbaudran conducted a chemical study of zinc blende from the Pierrefitte metallurgical plant in the Pyrenees. This research proceeded slowly and ended with the discovery in 1875. a new element, gallium, named after France, which the ancient Romans called Gaul. News of the discovery appeared in the Reports of the Paris Academy of Sciences and in a number of other publications. D.I. Mendeleev, who closely followed the scientific literature, immediately recognized the new element as eka-aluminium, which he predicted, despite the fact that in the first message of the author of the discovery, gallium was described only in the most general terms and some of its properties were determined incorrectly. Thus, it was assumed that the specific gravity of eka-aluminum is 5.9, and the specific gravity of the open element is 4.7. D.I. Mendeleev sent L. De Boisbaudran a letter in which he not only drew attention to his work on the periodic law, but also pointed out an error in determining specific gravity. Lecoq de Boisbaudran, who had never heard of the Russian scientist or the periodic law of chemical elements discovered by him, received this speech with displeasure, but then, having become acquainted with D.I. Mendeleev’s article on the periodic law, he repeated his experiments and it really turned out that that the specific gravity predicted by D.I. Mendeleev exactly coincided with that determined experimentally by L. de Boisbaudran. This circumstance, of course, could not fail to make a very strong impression both on Lecoq de Boisbaudran himself and on the entire scientific world. Thus, D.I. Mendeleev’s foresight was brilliantly justified (Appendix Table 5). The entire history of the discovery and study of gallium compounds, which received coverage in the literature of that time, involuntarily attracted the attention of chemists and became the first impetus for the universal recognition of the periodic law. The demand for the main work of D.I. Mendeleev, The Periodic Law of Chemical Elements, published in the Annals of Liebig, turned out to be so great that it needed to be translated into English and French, and many scientists sought to contribute to the search for new, still unknown elements predicted and described by D. I. Mendeleev. These are V. Crooks, V. Ramsay, T. Carnelli, T. Thorpe, G. Hartley - in England; P. Lecoq de Boisbaudran, C. Marignac - in France; K. Winkler - in Germany; J. Thomsen - in Denmark; I. Rydberg - in Sweden; B. Brauner - in the Czech Republic, etc. D.I. Mendeleev called them strengtheners of the law. In laboratories various countries Chemical analytical studies began.

Professor of analytical chemistry at Uppsala University L.F. Nilsson was one of these scientists. Working with the mineral euxenite, which contains rare earth elements, he obtained, in addition to the main product, some kind of earth (oxide) unknown to him. With a careful and detailed study of this unknown land in March 1879. Nilsson discovered new element, the main properties of which coincided with the properties described by D.I. Mendeleev in 1871. ekabor. This new element was named scandium in honor of Scandinavia, where it was discovered and found its place in the third group of the periodic table of elements between calcium and titanium, as predicted by D.I. Mendeleev (Appendix Table 6). The history of the discovery of ecaboron-scandium once again clearly confirmed not only the bold predictions of D.I. Mendeleev, but also the extreme importance for science of the periodic law discovered by him. After the discovery of gallium, it became absolutely obvious that the periodic law is, in the full sense of the word, a guiding star of chemistry, indicating in which direction the search for new, still unknown chemical elements should be carried out.

A few years after the discovery of scandium, more precisely in 1886, the periodic law again attracted widespread attention. In Germany, near Freiberg, in the area of ​​Mount Himmelsfürst, a new unknown mineral was found in a silver mine. Professor A. Weisbach, who discovered this mineral, called it argyrodite. A qualitative analysis of the new mineral was carried out by the chemist G.T. Richter, and a quantitative analysis by the famous analytical chemist K.A. Winkler. During his research, Winkler received an unexpected and strange result. It turned out that the total percentage of elements that make up argyrodite is only 93%, and not 100%, as it should be. Obviously, some element, which was also contained in a significant amount in the mineral, was missed during the analysis. Eight repeated tests, performed with extreme care, gave the same result. Winkler assumed that he was dealing with an element that had not yet been discovered. He named this element germanium and described its properties. A thorough study of the properties of germanium and its compounds soon led Winkler to the undoubted conclusion that the new element was D.I. Mendeleev’s eca-silicon (Appendix Table 7). Such an unusually close coincidence of the predicted and experimentally found properties of germanium amazed scientists, and Winkler himself, in one of his communications to the German Chemical Society, compared the prediction of D.I. Mendeleev with the predictions of astronomers Adams and Le Verrier about the existence of the planet Neptune, made only on the basis of calculations.

The brilliant confirmation of the predictions of D.I. Mendeleev had a great influence on the further development of chemistry and all natural sciences. Since the mid-80s. The periodic law was, of course, recognized by the entire scientific world and entered the arsenal of science as the basis of scientific research. From that time on, on the basis of the periodic law, a systematic study of the compounds of all known elements and the search for unknown but foreseeable compounds began. If before the discovery of the periodic law, scientists who studied various, especially newly discovered, minerals worked essentially blindly, not knowing where to look for new, unknown elements and what their properties should be, then, based on the periodic law, the discovery of new elements turned out to be possible almost without any surprises. The periodic law made it possible to accurately and unambiguously establish the number of not yet discovered elements with atomic weights ranging from 1 to 238 - from hydrogen to uranium. Over the course of just fifteen years, all the predictions of the Russian researcher were fulfilled, and the hitherto empty places in the system were filled with new elements with precisely calculated properties in advance. However, even during the life of D.I. Mendeleev, the periodic law was twice subjected to serious tests. New discoveries at the beginning seemed not only inexplicable from the point of view of the periodic law, but even contradicting it. So, in the 90s, W. Ramsay and J. W. Raleigh discovered a whole group of inert gases. For D.I. Mendeleev, this discovery in itself was not a complete surprise. He assumed the possibility of the existence of argon and other elements - its analogues - in the corresponding cells of the periodic table. However, the properties of the newly discovered elements and, above all, their inertness (zero valency) caused serious difficulties in placing new gases in the periodic table. It seemed that there were no places for these elements in the periodic table and D.I. Mendeleev did not immediately agree with the addition of a zero group to the periodic system. But it soon became obvious that the periodic system passed the test with honor and, after introducing the zero group into it, acquired an even more harmonious and complete appearance. At the turn of the 19th and 20th centuries, radioactivity was discovered. The properties of radioactive elements were so inconsistent with traditional ideas about elements and atoms that doubt arose about the validity of the periodic law. In addition, the number of newly discovered radioactive elements turned out to be such that seemingly insurmountable difficulties arose with the placement of these elements in the periodic table. However, soon, albeit after the death of D.I. Mendeleev, the difficulties that arose were completely eliminated, and the periodic law acquired additional features and a new meaning, which led to the expansion of its scientific significance.

In the twentieth century, Mendeleev's doctrine of periodicity remains one of the foundations of modern ideas about the structure and properties of matter. This doctrine includes two central concepts - the law of periodicity and the periodic system of elements. The system serves as a kind of graphic expression of the periodic law, which, unlike many other fundamental laws of nature, cannot be expressed in the form of any mathematical equation or formula. Throughout the twentieth century, the content of the doctrine of periodicity constantly expanded and deepened. This is also an increase in the number of chemical elements found in nature and synthesized. For example, europium, lutetium, hafnium, rhenium are stable elements existing in the earth's crust; radon, francium, protactinium - natural radioactive elements; technetium, promethium, astatine - synthesized elements. The placement of some new elements in the periodic table did not cause difficulties, since there were natural gaps in certain of its subgroups (hafnium, rhenium, technetium, radon, astatine, etc.). Lutetium, promethium, and europium turned out to be members of the rare earth family, and the question of their place became an integral part of the problem of the placement of rare earth elements. The problem of the place of transactinian elements is still debatable. Thus, new elements in a number of cases required additional development of ideas about the structure of the periodic table. A detailed study of the properties of elements led to unexpected discoveries and the establishment of new important patterns. The phenomenon of periodicity turned out to be much more complex than it was imagined in the 19th century. The fact is that the principle of periodicity, found by D.I. Mendeleev for chemical elements, turned out to be extended to atoms of elements, to the atomic level of organization of matter. Periodic changes in the properties of elements are explained by the existence of electronic periodicity, the repetition of similar types of electronic configurations of atoms as the charges of their nuclei increase. If at the elemental level the periodic table represented a generalization of empirical facts, then at the atomic level this generalization received theoretical basis. Further deepening of ideas about periodicity proceeded in two directions. One is related to the improvement of the theory of the periodic table due to the advent of quantum mechanics. Others directly relate to attempts to systematize isotopes and develop nuclear models. It was along this path that the concept of nuclear (nucleon) periodicity arose. Nuclear periodicity has a qualitatively different character compared to electronic periodicity (if Coulomb forces act in atoms, then specific nuclear forces manifest themselves in nuclei). Here we are faced with an even deeper level of manifestation of periodicity - nuclear (nucleon), characterized by many specific features.

So the history of the periodic law provides an interesting example of discovery and provides a criterion for judging what a discovery is. D.I. Mendeleev repeated many times that the true law of nature, which provides opportunities for foresight and prediction, should be distinguished from randomly observed patterns and correctness. The discovery of gallium, scandium and germanium predicted by scientists demonstrated the enormous importance of scientific foresight based on a solid foundation of theoretical principles and calculations. D.I. Mendeleev was not a prophet. It was not the intuition of a talented scientist, not some special ability to foresee the future that was the basis for describing the properties of elements not yet discovered. Only an unshakable confidence in the justice and enormous scientific significance of the periodic law he discovered, and an understanding of the significance of scientific foresight, gave him the opportunity to appear before the scientific world with bold and seemingly incredible predictions. D.I. Mendeleev passionately wanted the universal law of nature discovered by him to become the basis and guide for further attempts by mankind to penetrate the secrets of the structure of matter. He said that the laws of nature do not tolerate exceptions and therefore expressed with complete confidence what was a direct and obvious consequence of the open law. At the end of the 19th and 20th centuries, the periodic law was subjected to serious tests. More than once it seemed that the newly established facts contradicted the periodic law. This was the case with the discovery of noble gases and the phenomena of radioactivity, isotopy, etc. Difficulties arose with the placement of rare earth elements in the system. But, despite everything, the periodic law has proven that it is indeed one of the fundamental great laws of nature. All further development of chemistry took place on the basis of the periodic law. On the basis of this law, the internal structure of atoms was established and the patterns of their behavior were clarified. The periodic law is rightfully called a guiding star in the study of chemistry, in orienting oneself in the most complex labyrinth of the infinite variety of substances and their transformations. This is confirmed by the discovery of a new, 118th element of the periodic table by Russian and American scientists in the city of Dubna (Moscow region). According to the director of the Joint Institute for Nuclear Research, corresponding member of the Russian Academy of Sciences A. Sissakyan, scientists saw this element with the help of physical accelerators in laboratory conditions. Element 118 is by far the heaviest of all the elements in the periodic table that exist on Earth. This discovery once again confirmed the truth that the periodic law - the great law of nature, discovered by D.I. Mendeleev, remains unshakable.

The triumph of the periodic law was a triumph for D.I. Mendeleev himself. In the 80s, he, previously well known among scientists in Western Europe for his outstanding research, acquired high prestige throughout the world. The most prominent representatives of science showed him all sorts of signs of respect, admiring his scientific feat. D.I. Mendeleev was elected a member of many foreign academies of sciences and scientific societies, received many honorary titles, distinctions and awards.

In 1869, the great Russian chemist D.I. Mendeleev made a discovery that determined the further development of not only chemistry itself, but also many other sciences.

The entire prehistory of the discovery of the periodic law does not represent a phenomenon that goes beyond the scope of ordinary historical and scientific phenomena. In the history of science it is hardly possible to point out an example of the appearance of major generalizations that were not preceded by a long and more or less complex prehistory. As D.I. Mendeleev himself noted, there is not a single general law of nature that would be established immediately. Its approval is always preceded by many premonitions, and recognition of the law does not occur from the moment the first thought about it arises, and not even when it is fully realized in all its meaning, but only after the confirmation of its consequences by experiments, which should be recognized as the highest authority of considerations and opinions. . Indeed, one can state at first the appearance of only partial, sometimes even random observations and comparisons. Variants of such comparisons with the simultaneous expansion of the compared factual data sometimes lead to partial generalizations, devoid, however, of the main features of the law of nature. This is exactly what all Domendeley's attempts to systematize elements are like, including the tables of Newlands, Odling, Meyer, the Chancourtois schedule and others. Unlike his predecessors, D.I. Mendeleev did not look for specific laws, but sought to solve a general problem of a fundamental nature. At the same time, again, unlike his predecessors, he operated with verified quantitative data, and personally tested experimentally questionable characteristics of the elements. It can be definitely stated that all previous scientific activity led him to the discovery of the periodic law, that this discovery was the completion of D. I. Mendeleev’s earlier attempts to study and compare the physical and chemical properties of various substances, to accurately formulate the idea of ​​​​a close internal connection between various substances and first of all - between chemical elements. If we do not take into account the scientist’s early research on isomorphism, internal cohesion in liquids, solutions, etc., then it would be impossible to explain the sudden discovery of the periodic law. One cannot help but be amazed by the genius of D.I. Mendeleev, who managed to grasp the great unity in the immense chaos, in the disorder of disparate facts and information accumulated by chemists before him. He was able to establish the natural law of chemical elements at a time when almost nothing was known about the structure of matter.

So, by the end of the 19th century, as a result of the discovery of the periodic law, the following picture of the development of inorganic chemistry emerged. By the end of the 90s, the law received universal recognition, allowed scientists to anticipate new discoveries and systematize accumulating experimental material, and played an outstanding role in the substantiation and further development of atomic-molecular science. The periodic law stimulated the discovery of new chemical elements. Since the discovery of gallium, the system's predictive capabilities have become apparent. But at the same time, they were still limited due to ignorance of the physical causes of periodicity and a certain imperfection in the structure of the system. With the discovery of helium and argon on Earth, the English scientist V. Ramsay ventured to predict other, still unknown noble gases - neon, krypton and xenon, which were soon discovered. In the periodic system, published in the eighth edition of the textbook Fundamentals of Chemistry in 1906, D.I. Mendeleev included 71 elements. This table summarized the enormous work of discovery, study and systematics of elements over 37 years. Gallium, scandium, germanium, radium, and thorium found their place here; five noble gases formed the zero group. In the light of the periodic law, many concepts of general and inorganic chemistry acquired a more rigorous form (chemical element, simple body, valency). By the fact of its existence, the periodic table greatly contributed to the correct interpretation of the results achieved in the study of radioactivity and helped determine the chemical properties of the elements being detected. Thus, without the system, the inert nature of the emanations, which later turned out to be isotopes of the heaviest noble gas - radon, could not be understood. But classical physicochemical research methods were unable to solve the problems associated with the analysis of the causes of various deviations from the periodic law, but they largely prepared the basis for revealing the physical meaning of the place of an element in the system. The study of various physical, mechanical, crystallographic and chemical properties of elements showed their general dependence on the deeper and hidden for that time internal properties of atoms. D.I. Mendeleev himself was clearly aware that the periodic variability of simple and complex bodies is subject to some higher law, the nature of which, much less the cause, there was still no means to comprehend. Science has yet to solve this problem.

At the beginning of the twentieth century, the periodic system faced such a serious obstacle as the massive discovery of radioelements. There was not enough space for them in the periodic table. This difficulty was overcome six years after the scientist’s death thanks to the formulation of the concepts of isotopy and the charge of the atomic nucleus, numerically equal to the atomic number of the element in the periodic table. The doctrine of periodicity has entered a new, physical stage of its development. The most important achievement was the explanation of the physical reasons for the periodic changes in the properties of elements and, as a consequence, the structure of the periodic table. It was the periodic system of elements that served N. Bohr as the most important source of information when developing the theory of the structure of atoms. And the creation of such a theory meant the transition of Mendeleev’s doctrine of periodicity to a new level - atomic, or electronic. The physical reasons for the manifestation of a wide variety of properties by chemical elements and their compounds, which remained incomprehensible to the chemistry of the 19th century, became clear. During the 20s and 30s, almost all stable isotopes of chemical elements were discovered; currently their number is approximately 280. In addition, over 40 isotopes of radioactive elements have been discovered in nature, and about 1,600 artificial isotopes have been synthesized. The patterns of distribution of elements in the periodic table made it possible to explain the phenomenon of isomorphism - the replacement of atoms and atomic groups in the crystal lattices of minerals by other atoms and atomic groups.

The doctrine of periodicity in the development of geochemistry is of great importance. This science arose in the last quarter of the 19th century, when they began to intensively study the problem of the abundance of elements in the earth's crust and the patterns of their distribution in various ores and minerals. The periodic table has contributed to the identification of many geochemical patterns. Certain fields-blocks were identified, covering geochemically similar elements, and the idea of ​​similarities and differences between elements located along the diagonals of the system was developed. In turn, this made it possible to study the laws of the release of elements during the geological development of the earth’s crust and their joint presence in nature.

The twentieth century is called the century of the widest use of catalysis in chemistry. And here the periodic table serves as the basis for systematizing substances with catalytic properties. Thus, it was found that for heterogeneous oxidation-reduction reactions, all elements of the side subgroups of the table have a catalytic effect. For reactions of acid-base catalysis, which in industrial conditions include, for example, cracking, isomerization, polymerization, alkylation, etc., the catalysts are alkali and alkaline earth metals: Li, Na, K, Rb, Cs, Ca; in acid reactions - all p-elements of the second and third periods (except Ne and Ar), as well as Br and J.

Problems of cosmochemistry are also solved on the basis of the nuclear level of ideas about periodicity. Study of the composition of meteorites and lunar soil, data obtained by automatic stations on Venus and Mars show that these objects contain the same chemical elements that are known on Earth. Thus, the law of periodicity is applicable to other areas of the Universe.

One could name many more areas of scientific research where the periodic table of elements acts as a necessary tool of knowledge. It is not for nothing that in his report at the Anniversary Mendeleev Congress, dedicated to the centenary of the discovery of the periodic law, Academician S.I. Volfkovich said that the periodic law was a major milestone in the history of chemistry. It was the source of countless studies by chemists, physicists, geologists, astronomers, philosophers, historians, and continues to diversify influence biology, astronomy, technology and other sciences. And I would like to finish my work with the words of the German physicist and chemist W. Meyer, who wrote that Mendeleev’s courage of thought and insight will always evoke admiration (Yu. Solovyov. History of Chemistry).