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Mendeleyev, Dmitry Ivanovich, Mendeleyev also spelled MENDELEEV (b. Feb. 8 [Jan. 27, Old Style], 1834, Tobolsk, Siberia, Russia--d. Feb. 2 [Jan. 20], 1907, St. Petersburg), Russian chemist who developed the periodic classification of the elements. In his final version of the periodic table (1871) he left gaps, foretelling that they would be filled by elements not then known and predicting the properties of three of those elements.

Early life and education.

Mendeleyev was the 17th and last child of the director of the gymnasium at Tobolsk. In the same year his father became blind, and, in order to support the family, his mother leased and operated a glass factory in a town 20 miles (32 km) away. At school Dmitry excelled in mathematics, physics, and geography but fared badly in the compulsory classical languages. In 1847 his father died, and the next year fire destroyed the glass factory. Faced with these disasters, his mother made a brave decision: she turned her back on Tobolsk and, with her only two dependent children (Dmitry and his sister), set out for Moscow to place her son in the university.

Notwithstanding her good connections, she could not prevail in the face of the inflexible regulations that restricted admission according to place of origin: Siberia was outside the academic pale. She pressed on to St. Petersburg, but the university there, too, was closed to her son. Dmitry was also refused admission to the medical school, but, 10 weeks before her death, his mother finally secured him a place in the Pedagogic Institute.

In 1855 he qualified as a teacher, winning a gold medal for his academic achievements. On account of his health, he was posted, at his own request, to the Crimea, where he continued his chemical studies at Odessa; he returned to St. Petersburg in 1856 to obtain an advanced degree in chemistry. In 1857 he received his first university appointment. In 1859 the government sent him for further study to the University of Heidelberg. Although Robert Bunsen, the chemist and inventor, and the physicist Gustav Kirchhoff were then the dominant figures in the natural sciences at Heidelberg, Mendeleyev preferred to work independently. His study of molecular cohesion was begun at this time, and while at Heidelberg he attended the celebrated Karlsruhe conference (September 1860) and made valuable contacts with French chemists and with the Italian chemist Stanislao Cannizzaro, whose insistence on the distinction between molecular and atomic weights influenced Mendeleyev considerably.
In 1861 Mendeleyev returned to St. Petersburg. The lack of a permanent position led him to take up editing and scientific writing. In 1864 he became professor of chemistry at the Technical Institute, and three years later he was made professor of general chemistry at the university there. Since he could not find a textbook that met his needs, he set about writing his own: the result was The Principles of Chemistry (1868-70), a classic textbook.

Formulation of the periodic law.

In the course of writing the book, Mendeleyev probed deeply into the relationship between the properties of elements in an attempt to devise a system of classifying them. Other scientists had also tried to construct such a system of classification. After the English chemist and physicist John Dalton had developed the idea of atomic weights, chemists sought arithmetic connections between them, partly to see whether there was any likelihood of all elements being composed of a simple, common substance and partly to see whether occasional similarities in their properties pointed to similarities in structure. Johann Döbereiner and William Odling, both of whom had also done work with atomic weights, were the most prominent among the chemists who attempted to devise a logical order for the elements. It was Mendeleyev, however, who formulated the periodic law, according to which, when all known elements are arranged in order of increasing atomic weight, the resulting table shows a periodicity of properties and allows one to observe the many types of chemical relation hitherto studied only in isolation. The new system did not win wide acceptance at first, its validity becoming apparent only with time. The table of elements had gaps, but Mendeleyev predicted that they would be filled by elements not yet discovered; three were discovered within 20 years, and they possessed the properties he had predicted. Gradually the table became the framework for a great part of chemical theory and proved to be most useful in the interpretation of the processes of the natural transformation of one element into another, called radioactive decay, more than 20 years after the table's conception.
Although Mendeleyev's textbooks ran to many editions in many languages, the periodic theory remained his chief monument. Mendeleyev's mind, however, was not limited to theory and to classroom teaching. He was also by nature a practical man, aware of the necessity to use science in solving the problems of the world. In 1865 he farmed a small estate and improved the yield and quality of crops by the application of his scientific knowledge, a measure he knew was essential to the improvement of the general agricultural condition of Russia.

Other pursuits.

In 1867 he was sent to organize the Russian pavilion at the Paris Exposition of that same year. His study of the French chemical industry during his stay helped him improve the Russian soda industry, and, later, he spent much time working on the problems of the Russian petroleum industry. During a visit to the United States in 1876, he criticized the manner in which American oil interests concentrated on mere expansion of production without giving attention to scientific improvements of either the efficiency of the industry or the quality of its products. At home he was equally critical of the way Russian oil was exploited by foreign interests, and he constantly urged that Russia develop its own oil for its own profit. His interest in aeronautics led him to make balloon ascents for scientific observation and to encourage his colleagues to pursue the possibilities of heavier-than-air flight.
Politically, Mendeleyev held progressive views and was much interested in social reform. The tsarist regime did not approve of his political views, and, although a man of his stature could not be suppressed, he was often snubbed--as, for example, in 1880, when he was ostentatiously refused advancement from corresponding to full membership of the Imperial Academy of Sciences. In 1890 Mendeleyev's transmittal of a request from students at the university for alleviation of unjust conditions led to an open clash between him and the government. For this allegedly improper action he was retired from the university. He held no further major academic post. He was too useful, however, to be left idle. In 1891 he was officially employed in setting up a new system of import duties on heavy chemicals, and in 1893 he headed the Bureau of Weights and Measures, a post he filled efficiently until his death.
Mendeleyev's last years were saddened not only by declining health but by the political events that preceded the Russian Revolution of 1905. He had been greatly honoured by colleagues of many countries as a guest lecturer and as an honorary member of academies. He was recognized in his day as a leader of the movement to systematize and make cohesive the study of chemistry. He is recognized now as the discoverer of the interrelationship of chemical elements, which not only underlies most of chemistry but also unifies a great deal of modern physics. (F.Gre.)

BIBLIOGRAPHY.

The only substantial biography in English is Daniel Q. Posin, Mendeleyev: The Story of a Great Scientist (1948), but it is also a fanciful and romanticized version. Studies of Mendeleyev's scientific work are included in J.R. Partington, A History of Chemistry, vol. 4, ch. 26 (1964), which also gives biographical notes on and estimates of the work of his principal contemporaries, with many references.