February 8, 1834: Dmitri Ivanovich Mendeleev is born
Dmitri Ivanovich Mendeleev (1834-1907)
Scientific field: Chemistry
Known for: the Periodic Table of Elements
Dmitri Mendeleev (also spelled Meneleyev) was a 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.
In 1855 he qualified as a teacher at the Pedagogic Institute in St. Petersburg, 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 and,in 1857, he received his first university appointment.
In 1859 the government sent him for further study to the University of Heidelberg where he 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, after returning 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.
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 Mendeleev 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.(1)
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