Periodic table

The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. First created by Dmitri Mendeleev, the elements are arranged by electron configuration so that many chemical properties follow a regular pattern across the table. Each element is listed by its atomic number and chemical symbol. Mendeleev's ordering of the periodic table was one of the greatest developments in modern chemistry. Chemists were able to quantitatively explain the behavior of the elements, and to predict the existence of yet undiscovered ones. There are 116 chemical elements whose discoveries has been confirmed. Ninety four can be found naturally on Earth, and the rest have been produced in laboratories.

History

Main article: History of the periodic table

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The original table was created without a knowledge of the inner structure of atoms: if one orders the elements by atomic mass, and then plots certain other properties against atomic mass, one sees an undulation or periodicity to these properties as a function of atomic mass.

Related Topics:
Atom - Atomic mass

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The first to recognize these regularities was the German chemist Johann Wolfgang Döbereiner who, in 1829, noticed a number of triads of similar elements:

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This was followed by the English chemist John Newlands, who in 1865 noticed that the elements of similar type recurred at intervals of eight, which he likened to the octaves of music, though his law of octaves was ridiculed by his contemporaries. Finally, in 1869, the German Julius Lothar Meyer and the Russian chemist Dmitri Ivanovich Mendeleev almost simultaneously developed the first periodic table, arranging the elements by mass. However, Mendeleev plotted a few elements out of strict mass sequence in order to make a better match to the properties of their neighbours in the table, corrected mistakes in the values of several atomic masses, and predicted the existence and properties of a few new elements in the empty cells of his table. Mendeleev was later vindicated by the discovery of the electronic structure of the elements in the late 19th and early 20th century.

Related Topics:
John Newlands - Octaves of music - Julius Lothar Meyer - Dmitri Ivanovich Mendeleev - 19th - 20th century

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In the 1940s Glenn T. Seaborg identified the transuranic lathanides and the actinides, which may be placed within the table, or below (as shown above).

Related Topics:
Glenn T. Seaborg - Transuranic

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