Dmitri Mendeleev

Dmitri Ivanovich Mendeleyev ({{lang-ru|???????? ????????? ??????????}} {{Audio|ru-Dmitri_Mendeleev.ogg|listen}}) ({{OldStyleDate|8 February|1834|27 January}} in Tobolsk – {{OldStyleDate|2 February|1907|20 January}} in Saint Petersburg), was a Russian chemist. He is renowned for being one of the two scientists who created the first version of the periodic table of elements. Unlike other contributors to the table, Mendeleyev managed to predict the properties of elements yet to be discovered. In several cases he even ventured to question the accuracy of the accepted atomic weights, arguing that they did not correspond to those predicted by the Periodic Law, and here too subsequent research proved him correct.

Periodic Table

In 1866, Newlands published his Law of Octaves. However, the lack of spaces for undiscovered elements and the placing of two elements in one box were criticised and his ideas were not accepted. Unaware of this, Mendeleev had been working on a similar idea, and on March 6, 1869, a formal presentation was made to the Russian Chemical Society, entitled The Dependence Between the Properties of the Atomic Weights of the Elements, stating

Related Topics:
1866 - Newlands - March 6 - 1869

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• The elements, if arranged according to their atomic weights, exhibit an apparent periodicity of properties.
• Elements which are similar as regards to their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).
• The arrangement of the elements, or of groups of elements in the order of their atomic weights, corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, Ba, C, N, O, and Sn.
• The elements which are the most widely diffused have small atomic weights.
• The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.
• We must expect the discovery of many as yet unknown elements–for example, elements analogous to aluminum and silicon–whose atomic weight would be between 65 and 75.
• The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128.
• Certain characteristic properties of elements can be foretold from their atomic weights.

Unknown to Mendeleyev, Lothar Meyer was also working on a periodic table. In his work published in 1864, Meyer presented only 28 elements, classified not by atomic weight but by valence alone. Also, Meyer never came to the idea of predicting new elements and correcting atomic weights. Only a few months after Mendeleev published his periodic table of all known elements (and predicted several new elements to complete the table, plus some corrected atomic weights), Meyer published a virtually identical table. Some people consider Meyer and Mendeleyev the cocreators of the periodic table, although most agree that Mendeleyev's accurate prediction of the qualities of what he called eka-silicon (germanium), eka-aluminum (gallium), and eka-boron (scandium) lands him the lion's share of credit. In any case, at the time Mendeleyev's predictions greatly impressed his contemporaries and were eventually found to be correct.

Related Topics:
Lothar Meyer - Atomic weight - Valence - Germanium - Gallium - Scandium

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