EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY EMILIO SEGRE VISUAL ARCHIVES / AMERICAN INSTITUTE OF PHYSICS / SCIENCE PHOTO LIBRARY
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Mendeleev's periodic table of the elements as published in 1869, with several gaps and uncertainties. Russian chemist Dmitry Ivanovich Mendeleyev (1834-1907) worked on organising trends in atomic weights and valency. From this, he developed the first true periodic table of the elements (final version published in 1871). New elements were discovered that fit the gaps and had the properties predicted. The text at top and lower right is in Cyrillic. The gap at atomic weight 45 was filled by scandium (1879), and at atomic weights 68 and 70 by gallium (1875) and germanium (1886). Modern periodic tables contain 118 elements.
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