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2019 has been designated the International Year of the Periodic Table as it is the 150th Anniversary of the formulation of Mendeleev's Tabelle I

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1950

Sidgwick's Periodic Classification (Mendeleeff)

From N.V. Sidgwick, Chemical Elements and Their Compounds, vol. 1, Oxford University, London, p. xxviii (1950).

René Vernon writes:

"In this curious table the Lanthanides are located in group IIIA while the Actinides have been fragmented.

Instead:

• Ac, Th, and Pa are located in groups IIIA, IVA and VA under Lu, Hf, and Ta, respectively
• The uranides, U, Np, Pu, Am, and Cm, are located in group VIA, under W."

Sidgwick writes:

"This subgroup (VIA) consists of Cr, Mo, W, and U, to which the 'uranide' elements, Np, Pu, Am, and Cm (which might be assigned to any Group from III to VI) must now be added." (p. 998)

"...the trans-uranium elements 93–6... for the first time give clear evidence of the opening of the 'second rare earth series', the 'uranides', through the expansion of the fifth quantum group from 18 towards 32." (p. 1069)

"The question whether the fifth quantum group of electrons which is completed up to 18 in gold begins to expand towards 32, as the fourth does in cerium, has now been settled by the chemical properties of these newly discovered elements. In the Ln the beginning of the expansion is marked by the main valency becoming and remaining 3. With these later elements of the seventh period there is scarcely any sign of valencies other than those of the group until we come to uranium... Up to and including uranium, the group valency is always the stablest, but beyond this no further rise of valency occurs, such as we find in rhenium and osmium. Hence the point of departure of the new series of structures (corresponding to lanthanum in the first series) is obviously uranium, and the series should be called the uranides. (p. 1092):

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