Mendeleev, Dmitry (1834-1907)

Russian chemist

One of the most unlikely success stories in the history of chemistry is that of Dmitry Ivanovich Mendeleev (also Mendeléev, Mendeleef, and Mendeleeff). Mendeleev was born in Tobolsk in western Siberia on February 8, 1834. He was the youngest child in a family of either 14 or 17 children (records do not agree). His father, a teacher at the Tobolsk gymnasium (high school) lost his job after he became blind when Dmitry was still quite young. His mother tried to take over support of the family by building a glassworks in the nearby town of Axemziansk.

Mendeleev was an average student. He learned science from a brother-in-law who had been exiled to Siberia because of revolutionary activities in Moscow. Dmitry completed high school at the age of 16, but only after the family had experienced further misfortune—the death of his father and destruction of his mother's glassworks by fire. In 1850, his mother decided to see that her two youngest children received a college education. She and the children traveled by horse first to Moscow, then on to St. Petersburg. Through the efforts of a family friend, she was able to enroll Dmitry at the Central Pedagogical Institute in St. Petersburg. A few months later, Mendeleev's mother died.

Mendeleev graduated from the Pedagogical Institute in 1855 and then traveled to France and Germany for graduate study. While at Heidelberg with Robert Bunsen, he discovered the phenomenon of critical temperature , the highest temperature at which a liquid and its vapor can exist in equilibrium. Credit for this discovery is usually given to Thomas Andrews (1813–1885) who made the same discovery independently two years later.

In 1861, Mendeleev returned to St. Petersburg, where he became professor of chemistry at the Technological Institute. Six years later, he was also appointed professor of general chemistry at the University of St. Petersburg, a post he held until 1890. In that year, he resigned his university appointment in a dispute with the Minister of Education. Three years later he was appointed Director of the Bureau of Weights and Measures, a post he held until his death on February 2, 1907. Mendeleev is remembered as a brilliant scholar, interesting teacher, and prolific writer. Besides his career in chemistry, he was interested in art, education, and economics. He was a man of strong opinions who was not afraid to express them, even when they might offend others. He was apparently bypassed for a few academic appointments and honors because of his irascible nature.

The achievement with which Mendeleev's name will forever be associated was his development of the periodic law. In 1868, he set out to write a textbook in chemistry, Principles in Chemistry, that was later to become a classic in the field. Mendeleev wanted to find some organizing principle on which he could base his discussion of Earth's 63 chemical elements then known. After attending the Karlsruhe Congress in 1860, he thought that the atomic weights of the elements might provide that organizing principle. He began by making cards for each of the known elements. On each card, he recorded an element's atomic weight, valence, and other chemical and physical properties. Then he tried arranging the cards in various ways to see if any pattern emerged. Mendeleev was apparently unaware of similar efforts to arrange the elements according to their weights made by J. A. R. Newlands (1838–1898) only a few years earlier.

Eventually he was successful. He saw that, when the elements were arranged in ascending order according to their weights, their properties repeated in a predictable, orderly manner. That is, when the cards were laid out in sequence, from left to right, the properties of the tenth element (sodium) were similar to those of the second element (lithium), the properties of the eleventh element (magnesium) were similar to those of the third element (beryllium), and so on.

When Mendeleev arranged all 63 elements according to their weights, he found a few places in which the law appeared to break down. For example, tellurium and iodine were in the wrong positions when arranged according to their weights. Mendeleev solved this problem by inverting the two elements, that is, by placing them where they ought to be according to their properties, even if they were no longer in the correct sequence according to their weights.

Mendeleev hypothesized that the atomic weights for these two elements had been incorrectly determined. He happened to be incorrect in this assumption, and it was not until Henry Moseley discovered atomic numbers in 1914 that the real explanation for inversion was found.

Mendeleev made one other critical hypothesis. He found three places in the periodic table where elements appeared to be missing. The blank spaces occurred when Mendeleev insisted on keeping elements with like properties underneath each other in the table, regardless of their weights. He predicted not only that the three missing elements would be found, but also what the properties of those elements would be.

Mendeleev's law was soon vindicated when the three missing elements were found in 1875 (gallium), 1879 (scandium), and 1885 (germanium).

See also Alkaline Earth metals; Atomic mass and weight; Atomic theory; Atoms; Bohr model of the atom; Chemical bonds and physical properties; Chemical elements; Geochemistry