DIMITRI IVANOVICH MENDELEEV.
Died: 1907, Leningrad, Russia
Major Works: Osnovy khimii (Principles of Chemistry) (1868), "On the Place of Cerium in the System of Elements" (1870, in Russian), "The Periodic Law of the Chemical Elements" (1889, in English)
Elements placed according to the value of their atomic weights present a clear periodicity of properties.
Dimitri Ivanovich Mendeleev (or Mendeleyev), a researcher in many areas of physical chemistry, including the liquification and compressibility of gases, and active in developing procedures for modernizing the Russian iron, coal, and petroleum industry, is best known today for his discovery of the periodic table of elements. Proceeding by analysis of the nature of the elements known in the mid-1800s and using the recently standardized atomic weights, he arranged the elements in a table that graphically showed the relationship between them. In Mendeleev's later years, he was active in government service, becoming one of the czar's privy councillors and producing a series of reference books of industrial knowledge. He was honored for his work throughout Europe.
Born to an old merchant family in Tobolsk, Siberia, Mendeleev showed an early liking for science and industry. His mother owned a glass factory, and throughout his life he endeavored to apply the results of science to industry and commerce. After graduating from the gymnasium in Tobolsk, he studied at the Main Pedagogical Institute in Saint Petersburg, graduating in 1855. His work there prefigured his later career: He began to investigate the relationship between the crystal structure and the chemical composition of substances, and whether these properties have anything to do with molecular configuration. This was to develop into his success in correlating chemical properties and atomic weights in the periodic table. After 1857, he taught and experimented at the University of Saint Petersburg. Appointed to the chair of chemistry in 1867, he found it necessary to write a chemistry textbook for his classes. This book, Osnovy khimii (Principles of Chemistry) went through eight editions during his lifetime (1st ed., 1868-71: 8th ed., 1906) and was his chief work. While working on the first edition, he had the insight that produced the modern periodic table.
By the mid-1850s, it had been shown that the elements could be placed into categories according to similarity of chemical activity: Fluorine, chlorine, bromine, and iodine formed the halogen group; oxygen, sulfur, selenium, and tellurium were another group; nitrogen, phosphorus, arsenic, antimony, and bismuth a third. It had also become clear that an atom of any given element can combine only in certain ways with an atom or atoms of another element. A fluorine atom combines with one hydrogen atom, an oxygen atom with two, a nitrogen atom with three, a carbon atom with four, to form HF, [H.sub.2]O, [H.sub.3]N, and [H.sub.4]C, respectively (using modern notation). These ways of combining are called the valence of the element: Fluorine is said to have valence of one, oxygen two, nitrogen three, and so on. (The valence of an element may vary, and in modern physics the general concept of valence has been subdivided into more precise categories. Today valence is explained by the number of electrons in the outer shell of the atom, but this explanation was not available to Mendeleev, who in fact rejected the existence of the electron and the concept of the ion as an electrically charged particle.)
Several chemists had already drawn up charts that arrayed the elements in horizontal and vertical rows according to atomic weights. Indeed, the chemist Lothar Meyer had constructed a table much like Mendeleev's, but unfortunately had not published it. In writing Osnovy khimii, Mendeleev had the inspiration of arranging the elements according to their valence and their atomic weights, which had recently been standardized on an empirical basis--that is, solely according to their chemical properties--at the first International Chemical Congress at Karlsruhe in 1860, which he had attended. He noted that there were regular progressions in the differences between the atomic weights of the elements in each group (the elements in the vertical columns of the final periodic table). He cited the following examples:
Element Atomic Wt. Element Atomic Wt. Element Atomic Wt. Chlorine 35.5 Bromine 80 Tellerium 127 Potassium 39 Rubidium 85.4 Cesium 133 Calcium 40 Strontium 87.6 Barium 137
To complete the table, Mendeleev wrote the names of the elements, their atomic weights, and their chemical properties on cards and played "chemical solitaire" with them until he had the correct arrangement. (He was, in fact, fond of solitaire.) He made a table whose eight vertical columns contained elements of the same valence and whose horizontal rows arrayed the elements in order of ascending atomic weight.
Mendeleev arranged his table by logical deduction from chemical facts. Only in the twentieth century, after the researches of Rutherford, Bohr, and others had explicated the structure of the atom, could a physical explanation be given for the nature of each group. Mendeleev announced his discovery in several papers delivered in 1869 and in a later edition of Osnovy khimii he summarized the studies that had led to the discovery.
His periodic table was not readily accepted at first: The industrial, empirical chemists were not interested; others objected on the grounds that the atomic weights given for certain elements were incorrect, while still others claimed prior discovery. His atomic weights and the table gained general acceptance only when Mendeleev was able (1) by using his table, to correct the previously announced atomic weight of cerium (its place in the table implied an atomic weight of 138, instead of the accepted 92), and (2) from gaps in the table, to predict the discovery of new elements and forecast some of their properties. Specifically, he predicted new elements in the groups containing aluminum and silicon. When these elements were discovered (gallium, germanium, and scandium), Mendeleev's work was universally accepted as proven. He also predicted new elements falling between hydrogen and lithium, between fluorine and sodium, and between chlorine and potassium--these were helium, neon, and argon, discovered in the 1890s--and he suspected the existence of a series of elements that were later found to be the rare earths.
While working on the periodic table, Mendeleev was also studying gases. In 1860, he had discovered that each gas has a critical temperature, the temperature at which the gas may be liquified by pressure alone. In 1870--71, he turned to research on the cooling and compressibility of gases. While investigating gases, he hoped to find the ether, the universal fluid permeating the universe, which in his system must occupy the place just above hydrogen. Although this pursuit was chimerical, he did derive precise equations for the behavior of gases in a real--as contrasted with an ideal--environment. He then turned to atmospheric research, investigating the temperature of the upper atmosphere. He made a balloon ascent in 1887 to further these investigations.
In 1890, because of political upheavals at the University of Saint Petersburg, Mendeleev felt obliged to resign his professorship. His retirement was busy and full of honors: He was commissioned to do research on smokeless powder, he studied the tariff, he was director of the Central Board of Weights and Measures, and he helped design an icebreaker for Arctic research. He presented a summary of his work in English in his Faraday lecture, "The Periodic Law of the Chemical Elements" delivered in London on the twentieth anniversary of his discovery In 1902, he visited the Curies in Paris to study radioactivity. At his funeral in 1907, students of the University of Saint Petersburg lifted the periodic table of the element high above the procession as their tribute to the great scientist's career. In he modern periodic table, the transuranic element of atomic number 101, atomic weight 258, has been named mendelevium; thus contemporary physics commemorates the discoverer in his discovery.
Petrianov-Sokolov, I. V. Elementary Order: Mendeleev's Periodic System. Translated by N. Weinstein. Moscow: Mir Publishers, 1984. A discussion of the background and scientific basis for Mendeleev's primary work.
Pisarzhevskii, Oleg. Dimitry Ivanovich Mendeleyev, His Life and Work. Moscow: Foreign Languages Publishing House, 1954. One of the few biographies available in English. The biography by Daniel Posin, Mendeleyev: The Story of a Great Scientist, is a fictionalized narrative, difficult to take seriously.