Report: The periodic table and its significance in the development of chemistry by D. Mendeleev

The periodic table of elements had a great influence on the subsequent development of chemistry.

Dmitry Ivanovich Mendeleev (1834-1907)

Not only was it the first natural classification of chemical elements, showing that they form a harmonious system and are in close connection with each other, but it also became a powerful tool for further research.

At the time when Mendeleev compiled his table based on the periodic law he discovered, many elements were still unknown. Thus, the fourth period element scandium was unknown. In terms of atomic mass, titanium came after calcium, but titanium could not be placed immediately after calcium, since it would fall into the third group, while titanium forms a higher oxide, and according to other properties it should be classified in the fourth group. Therefore, Mendeleev skipped one cell, that is, he left free space between calcium and titanium. On the same basis, in the fourth period, two free cells were left between zinc and arsenic, now occupied by the elements gallium and germanium. There are still empty seats in other rows. Mendeleev was not only convinced that there must be as yet unknown elements that would fill these spaces, but he also predicted the properties of such elements in advance based on their position among other elements of the periodic table. He gave the name ekabor to one of them, which in the future was to take a place between calcium and titanium (since its properties were supposed to resemble boron); the other two, for which there were spaces left in the table between zinc and arsenic, were named eka-aluminum and eca-silicon.

Over the next 15 years, Mendeleev's predictions were brilliantly confirmed: all three expected elements were discovered. First, the French chemist Lecoq de Boisbaudran discovered gallium, which has all the properties of eka-aluminium; then, in Sweden, L. F. Nilsson discovered scandium, which had the properties of ekaboron, and finally, a few years later in Germany, K. A. Winkler discovered an element he called germanium, which turned out to be identical to ekasilicon.

To judge the amazing accuracy of Mendeleev’s foresight, let us compare the properties of eca-silicon predicted by him in 1871 with the properties of germanium discovered in 1886:

The discovery of gallium, scandium and germanium was the greatest triumph of the periodic law.

The periodic system was also of great importance in establishing the valence and atomic masses of some elements. Thus, the element beryllium has long been considered an analogue of aluminum and its oxide was assigned the formula. Based on the percentage composition and the expected formula of beryllium oxide, its atomic mass was considered to be 13.5. The periodic table has shown that there is only one place for beryllium in the table, namely above magnesium, so its oxide must have the formula , which gives the atomic mass of beryllium equal to ten. This conclusion was soon confirmed by determinations of the atomic mass of beryllium from the vapor density of its chloride.

Exactly And at present, the periodic law remains the guiding thread and guiding principle of chemistry. It was on its basis that transuranium elements located in the periodic table after uranium were artificially created in recent decades. One of them - element No. 101, first obtained in 1955 - was named mendelevium in honor of the great Russian scientist.

The discovery of the periodic law and the creation of a system of chemical elements was of great importance not only for chemistry, but also for philosophy, for our entire understanding of the world. Mendeleev showed that chemical elements form a harmonious system, which is based on a fundamental law of nature. This is an expression of the position of materialist dialectics about the interconnection and interdependence of natural phenomena. Revealing the relationship between the properties of chemical elements and the mass of their atoms, the periodic law was a brilliant confirmation of one of the universal laws of the development of nature - the law of the transition of quantity into quality.

The subsequent development of science made it possible, based on the periodic law, to understand the structure of matter much more deeply than was possible during Mendeleev’s lifetime.

The theory of atomic structure developed in the 20th century, in turn, gave the periodic law and the periodic system of elements a new, deeper illumination. The prophetic words of Mendeleev were brilliantly confirmed: “The periodic law is not threatened with destruction, but only superstructure and development are promised.”

The periodic table of elements had a great influence on the subsequent development of chemistry. Not only was it the first natural classification of chemical elements, showing that they form a harmonious system and are in close connection with each other, but it was also a powerful tool for further research.
At the time when Mendeleev compiled his table based on the periodic law he discovered, many elements were still unknown. Thus, the period 4 element scandium was unknown. In terms of atomic mass, Ti came after Ca, but Ti could not be placed immediately after Ca, because it would fall into group 3, but due to the properties of Ti it should be classified into group 4. Therefore, Mendeleev missed one cell. On the same basis, in period 4, two free cells were left between Zn and As. There are still empty seats in other rows. Mendeleev was not only convinced that there must be still unknown elements that would fill these places, but also predicted in advance the properties of such elements, based on their position among other elements of the periodic table. These elements were also given the names ekaboron (since its properties were supposed to resemble boron), ekaaluminium, ecasilicium...

D.I. Mendeleev wrote: “Before the periodic law, the elements represented only fragmentary random phenomena of nature; there was no reason to expect any new ones, and those found again were a complete unexpected novelty. The periodic pattern was the first to make it possible to see as yet undiscovered elements at a distance that vision unaided by this pattern had not yet reached.”

With the discovery of the Periodic Law, chemistry ceased to be a descriptive science - it received a tool of scientific foresight. This law and its graphic display - the table of the Periodic Table of Chemical Elements by D.I. Mendeleev - fulfilled all three most important functions of theoretical knowledge: generalizing, explanatory and predictive. Based on them, scientists:

• systematized and summarized all information about chemical elements and the substances they form;
• gave a rationale for the various types of periodic dependence existing in the world of chemical elements, explaining them on the basis of the structure of the atoms of the elements;
• predicted, described the properties of yet undiscovered chemical elements and the substances formed by them, and also indicated the ways of their discovery.

D. I. Mendeleev himself had to systematize and generalize information about chemical elements when he discovered the Periodic Law, built and improved his table. Moreover, errors in the values ​​of atomic masses and the presence of elements that had not yet been discovered created additional difficulties. But the great scientist was firmly convinced of the truth of the law of nature he discovered. Based on the similarity in properties and believing in the correct determination of the place of elements in the table of the Periodic System, he significantly changed the atomic masses and valence in compounds with oxygen of ten elements accepted at that time and “corrected” them for ten others. He placed eight elements in the table, contrary to the generally accepted ideas at that time about their similarity with others. For example, he excluded thallium from the natural family of alkali metals and placed it in group III according to the highest valence it exhibits; he transferred beryllium with an incorrectly determined relative atomic mass (13) and valence III from group III to II, changing the value of its relative atomic mass to 9 and the highest valency to II.

Most scientists perceived D.I. Mendeleev’s amendments as scientific frivolity and unfounded impudence. The periodic law and the table of chemical elements were considered as a hypothesis, that is, an assumption in need of verification. The scientist understood this and precisely to check the correctness of the law and system of elements he discovered, he described in detail the properties of elements that had not yet been discovered and even the methods of their discovery, based on their intended place in the system. Using the first version of the table, he made four predictions about the existence of unknown elements (gallium, germanium, hafnium, scandium), and according to the improved, second version, he made seven more (technetium, rhenium, astatine, francium, radium, actinium, protactinium).

During the period from 1869 to 1886, three predicted elements were discovered: gallium (P. E. Lecoq de Boisbaudran, France, 1875), scandium (L. F. Nilsson, Sweden, 1879) and germanium (C. Winkler, Germany, 1886). The discovery of the first of these elements, which confirmed the correctness of the great Russian scientist’s prediction, aroused only interest and surprise among his colleagues. The discovery of germanium was a true triumph of the Periodic Law. K. Winkler wrote in the article “Message on Germany”: “There is no longer any doubt that the new element is none other than eca-silicon predicted by Mendeleev fifteen years earlier. For a more convincing proof of the validity of the doctrine of the periodicity of elements can hardly be given than the embodiment of the hitherto hypothetical eca-silicon, and it truly represents something more than a simple confirmation of a boldly put forward theory - it means an outstanding expansion of the chemical field of vision, a mighty step in the field of cognition."

Based on the law and table of D.I. Mendeleev, noble gases were predicted and discovered. And now this law serves as a guiding star for the discovery or artificial creation of new chemical elements. For example, one could argue that element #114 is similar to lead (ekaslead) and #118 would be a noble gas (ekaradone).

The discovery of the Periodic Law and the creation of the table of the Periodic Table of chemical elements by D. I. Mendeleev stimulated the search for the reasons for the interconnection of elements, contributed to the identification of the complex structure of the atom and the development of the doctrine of the structure of the atom. This teaching, in turn, made it possible to reveal the physical meaning of the Periodic Law and explain the arrangement of elements in the Periodic Table. It led to the discovery of atomic energy and its use for human needs.

Questions and tasks for § 5

1. Analyze the distribution of biogenic macroelements by periods and groups of D. I. Mendeleev’s Periodic Table. Let us recall that these include C, H, O, N, Ca, S, P, K, Mg, Fe.
2. Why are the elements of the main subgroups of the 2nd and 3rd periods called chemical analogues? How does this analogy manifest itself?
3. Why is hydrogen, unlike all other elements, written twice in D.I. Mendeleev’s Periodic Table? Prove the validity of the dual position of hydrogen in the Periodic Table by comparing the structure and properties of its atom, simple substance and compounds with the corresponding forms of existence of other elements - alkali metals and halogens.
4. Why are the properties of lanthanum and lanthanides, actinium and actinides so similar?
5. What forms of compounds will be the same for elements of the main and secondary subgroups?
6. Why are the general formulas of volatile hydrogen compounds in the Periodic Table written only under the elements of the main subgroups, and the formulas of higher oxides - under the elements of both subgroups (in the middle)?
7. What is the general formula of the higher hydroxide corresponding to elements of group VII? What is his character?

In 1869, D.I. Mendeleev, based on an analysis of the properties of simple substances and compounds, formulated the Periodic Law: “The properties of simple bodies and compounds of elements are periodically dependent on the magnitude of the atomic masses of the elements.” Based on the periodic law, the periodic system of elements was compiled. In it, elements with similar properties were combined into vertical group columns. In some cases, when placing elements in the Periodic Table, it was necessary to disrupt the sequence of increasing atomic masses in order to maintain the periodicity of the repetition of properties. For example, it was necessary to “swap” tellurium and iodine, as well as argon and potassium. The reason is that Mendeleev proposed the periodic law at a time when nothing was known about the structure of the atom. After the planetary model of the atom was proposed in the 20th century, the periodic law is formulated as follows:

“The properties of chemical elements and compounds are periodically dependent on the charges of atomic nuclei.”

The charge of the nucleus is equal to the number of the element in the periodic table and the number of electrons in the electron shell of the atom. This formulation explained the "violations" of the Periodic Law. In the Periodic Table, the period number is equal to the number of electronic levels in the atom, the group number for elements of the main subgroups is equal to the number of electrons in the outer level.

Scientific significance of the periodic law. The periodic law made it possible to systematize the properties of chemical elements and their compounds. When compiling the periodic table, Mendeleev predicted the existence of many undiscovered elements, leaving empty cells for them, and predicted many properties of undiscovered elements, which facilitated their discovery. The first of these followed four years later.

But Mendeleev’s great merit is not only in the discovery of new things.

Mendeleev discovered a new law of nature. Instead of disparate, unconnected substances, science faced a single harmonious system that united all the elements of the Universe into a single whole; atoms began to be considered as:

1. organically connected with each other by a common pattern,

2. detecting the transition of quantitative changes in atomic weight into qualitative changes in their chemical. individualities,

3. indicating that the opposite is metallic. and non-metallic. properties of atoms is not absolute, as previously thought, but only relative in nature.

24. The emergence of structural theories in the process of development of organic chemistry. Atomic-molecular science as a theoretical basis for structural theories.

Organic chemistry. Throughout the 18th century. In the question of the chemical relationships of organisms and substances, scientists were guided by the doctrine of vitalism - a doctrine that considered life as a special phenomenon, subject not to the laws of the universe, but to the influence of special vital forces. This view was inherited by many 19th-century scientists, although its foundations were shaken as early as 1777, when Lavoisier suggested that respiration was a process similar to combustion.

In 1828, the German chemist Friedrich Wöhler (1800–1882), by heating ammonium cyanate (this compound was unconditionally classified as an inorganic substance), obtained urea, a waste product of humans and animals. In 1845, Adolf Kolbe, a student of Wöhler, synthesized acetic acid from the starting elements carbon, hydrogen and oxygen. In the 1850s, the French chemist Pierre Berthelot began systematic work on the synthesis of organic compounds and obtained methyl and ethyl alcohols, methane, benzene, and acetylene. A systematic study of natural organic compounds has shown that they all contain one or more carbon atoms and many contain hydrogen atoms. Type theory. The discovery and isolation of a huge number of complex carbon-containing compounds raised the question of the composition of their molecules and led to the need to revise the existing classification system. By the 1840s, chemical scientists realized that Berzelius's dualistic ideas only applied to inorganic salts. In 1853, an attempt was made to classify all organic compounds by type. A generalized "type theory" was proposed by a French chemist Charles Frederic Gerard, who believed that the combination of different groups of atoms is determined not by the electric charge of these groups, but by their specific chemical properties.

Structural chemistry. In 1857, Kekule, based on the theory of valence (valence was understood as the number of hydrogen atoms that combine with one atom of a given element), suggested that carbon is tetravalent and therefore can combine with four other atoms, forming long chains - straight or branched. Therefore, organic molecules began to be depicted not in the form of combinations of radicals, but in the form of structural formulas - atoms and bonds between them.

In 1874, a Danish chemist Jacob van't Hoff and the French chemist Joseph Achille Le Bel (1847–1930) extended this idea to the arrangement of atoms in space. They believed that molecules were not flat, but three-dimensional structures. This concept made it possible to explain many well-known phenomena, for example, spatial isomerism, the existence of molecules of the same composition, but with different properties. The data fit very well into it Louis Pasteur about isomers of tartaric acid.

The periodic table of elements had a great influence on the subsequent development of chemistry.

Not only was it the first natural classification of chemical elements, showing that they form a harmonious system and are in close connection with each other, but it also became a powerful tool for further research.

At the time when Mendeleev compiled his table based on the periodic law he discovered, many elements were still unknown. Thus, the fourth period element scandium was unknown. In terms of atomic mass, titanium came after calcium, but titanium could not be placed immediately after calcium, since it would fall into the third group, while titanium forms a higher oxide, and according to other properties it should be classified in the fourth group. Therefore, Mendeleev skipped one cell, that is, he left free space between calcium and titanium. On the same basis, in the fourth period, two free cells were left between zinc and arsenic, now occupied by the elements gallium and germanium. There are still empty seats in other rows. Mendeleev was not only convinced that there must be as yet unknown elements that would fill these spaces, but he also predicted the properties of such elements in advance based on their position among other elements of the periodic table. He gave the name ekabor to one of them, which in the future was to take a place between calcium and titanium (since its properties were supposed to resemble boron); the other two, for which there were spaces left in the table between zinc and arsenic, were named eka-aluminum and eca-silicon.

Over the next 15 years, Mendeleev's predictions were brilliantly confirmed: all three expected elements were discovered. First, the French chemist Lecoq de Boisbaudran discovered gallium, which has all the properties of eka-aluminium; then, in Sweden, L. F. Nilsson discovered scandium, which had the properties of ekaboron, and finally, a few years later in Germany, K. A. Winkler discovered an element he called germanium, which turned out to be identical to ekasilicon.

To judge the amazing accuracy of Mendeleev’s foresight, let us compare the properties of eca-silicon predicted by him in 1871 with the properties of germanium discovered in 1886:

The discovery of gallium, scandium and germanium was the greatest triumph of the periodic law.

The periodic system was also of great importance in establishing the valence and atomic masses of some elements. Thus, the element beryllium has long been considered an analogue of aluminum and its oxide was assigned the formula. Based on the percentage composition and the expected formula of beryllium oxide, its atomic mass was considered to be 13.5. The periodic table has shown that there is only one place for beryllium in the table, namely above magnesium, so its oxide must have the formula, which gives the atomic mass of beryllium equal to ten. This conclusion was soon confirmed by determinations of the atomic mass of beryllium from the vapor density of its chloride.

Exactly<гак же периодическая система дала толчок к исправлению атомных масс некоторых элементов. Например, цезию раньше приписывали атомную массу 123,4. Менделев же, располагая элементы в таблицу, нашел, что по своим свойствам цезий должен стоять в главной подгруппе первой группы под рубидием и потому будет иметь атомную массу около 130. Современные определения показывают, что атомная масса цезия равна 132,9054.

And at present, the periodic law remains the guiding thread and guiding principle of chemistry. It was on its basis that transuranium elements located in the periodic table after uranium were artificially created in recent decades. One of them - element No. 101, first obtained in 1955 - was named mendelevium in honor of the great Russian scientist.

The discovery of the periodic law and the creation of a system of chemical elements was of great importance not only for chemistry, but also for philosophy, for our entire understanding of the world. Mendeleev showed that chemical elements form a harmonious system, which is based on a fundamental law of nature. This is an expression of the position of materialist dialectics about the interconnection and interdependence of natural phenomena. Revealing the relationship between the properties of chemical elements and the mass of their atoms, the periodic law was a brilliant confirmation of one of the universal laws of the development of nature - the law of the transition of quantity into quality.

The subsequent development of science made it possible, based on the periodic law, to understand the structure of matter much more deeply than was possible during Mendeleev’s lifetime.

The theory of atomic structure developed in the 20th century, in turn, gave the periodic law and the periodic system of elements a new, deeper illumination. The prophetic words of Mendeleev were brilliantly confirmed: “The periodic law is not threatened with destruction, but only superstructure and development are promised.”