February 17 (March 1), 1869 Dmitri Ivanovich Mendeleev sent to the printer’s his manuscript, "The experiment of a system of elements based on their atomic weight and chemical similarity", the first version of the periodic table of elements. The final wording of the law was given to scientists in July 1871.
The periodic law was discovered by Mendeleev in the course of composing "The Fundamentals of Chemistry" textbook when he had difficulty systemizing the facts. By mid-February 1869, considering the structure of the textbook, the scientist gradually came to the conclusion that the properties of simple substances and the atomic masses of elements are bound to a certain regularity.
The discovery of the periodic table of elements was not made by chance, it was the result of enormous effort, time-consuming and painstaking work done not only by Dmitri Ivanovich, but also by many chemists from among his predecessors and contemporaries. "When I was finishing drawing up my classification of the elements, I wrote down each element and its compounds on a slip, and then, placing them by groups and series, got the first visual table of the periodic law. But it was only the finale, the result of the previous work ...," said the scientist. Mendeleev stressed that his discovery was the result which had completed a twenty-year meditation on the relationship between the elements, thinking over the relationship of elements.
February 17 (March 1), the manuscript of the article containing the table entitled "The experiment of a system of elements based on their atomic weight and chemical similarity," was completed and sent to print with notes for typesetters dated "February 17, 1869." Mendeleev’s discovery was reported by the editor of the "Russian Chemical Society," Professor N. A. Menshutkin at the society’s meeting of 22 February (March 6) 1869. Mendeleev himself was not present at the meeting, as at that time, on the instructions of the Free Economic Society, was surveying cheese dairies in the Tver and Novgorod provinces.
In the first version of the system, the scholar organized the elements by nineteen horizontal rows and six vertical columns. February 17 (March 1) the discovery of the periodic law was not at all completed, but just began. Dmitri Ivanovich continued its development and deepening for almost three more years. In 1870 Mendeleev published the second version of the system ("The Natural System of Elements") in “The Principles of Chemistry": the horizontal columns of elements-analogs had been transformed into eight vertically arranged groups, while six vertical columns of the first version had become periods beginning with an alkali and ending with halogen. Each period was divided into two rows; the elements of different groups rows included in the group formed a series of subgroups.
The essence of the discovery of Mendeleev was the fact that as the atomic weight of chemical elements increased, their properties changed periodically, not monotonically. After a certain number of elements with different properties, arranged by growing atomic weight, the properties begin to repeat. The difference of Mendeleev's work from those of his predecessors was the fact that Mendeleev used two basis for his classification of the elements instead of one: the atomic mass and the chemical similarity. In order to fully maintain the periodicity, Mendeleev corrected the atomic weights of certain elements, matched some of them with other elements of his system despite the accepted notions of the time about their similarities, left empty squares in the table for the elements not yet discovered.
In 1871, on the basis of these studies; Mendeleev formulated the Periodic trends, whose form slightly improved over time.
The Periodic system of elements had a great impact on the further development of chemistry. Not only it was the first natural classification of the chemical elements, which demonstrated that they form a coherent system and are in close contact with each other, but also was a powerful instrument for further research. At the time when Mendeleev was drawing up his table in accordance with the periodic trends he had discovered, many elements were still unknown. Mendeleev was not only convinced that there must be yet unknown elements that would fill the gaps in his table, but had also predicted the properties of those elements considering their position among the other elements of the periodic system. Over the next 15 years, the predictions of Mendeleev brilliantly confirmed, all the three expected elements were discovered (Ga, Sc, Ge), which turned out to be the greatest triumph of the periodic trends.
The periodic system has also played an important role in determining the valence and the atomic weights of some elements. Similarly, the periodic system gave rise to the correction of the atomic masses of some elements. It was on its basis that transuranic elements have been artificially created. The further development of science, based on the periodic trends, allowed much deeper understanding of the structure of the substance, than it was possible during the life of Mendeleev. The scientist himself described his law as follows: "The future does not threaten the periodic trends the destruction, but will provide only improvement and development."
Lit.: Агафошин Н. П. Периодический закон и периодическая система элементов Д. И. Менделеева. М., 1973; Евдокимов Ю. К истории периодического закона // Наука и жизнь. № 5 (2009). С. 12—15; Кедров Б. M. День одного великого открытия. M., 1958; Кедров Б. M., Трифонов Д. H. Закон периодичности и химические элементы. Открытия и хронология. M., 1969; Макареня А. А., Рысев Ю. В. Д. И. Менделеев. М., 1983; Макареня А. А., Трифонов Д. Н. Периодический закон Д. И. Менделеева. М., 1969; Макареня А. А., Трифонов Д. Н. Периодический закон Д. И. Менделеева. М., 1969; Менделеев Д. И. Периодический закон. Основные статьи. M., 1958.
From the Presidential library materials: