The periodic table displays all the elements, arranged in order of their atomic number, summarising their major properties. The vertical columns (groups) are numbered I-VII and 0 to reflect the number of electrons in the outermost unfilled shell. A gradation of properties may be traced along the horizontal rows (periods). The first periodic table was devised by Rusian chemist Dmitry Mendeleyev (1834-1907) in 1869.
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