The periodic tables of Mendeleev
How Mendeleev corrected the atomic weights of In, Ce and U, and thus constructed the remarkable Periodic Table of 1871
What is important is that the Periodic Tables of 1869 and of 1871 are totally different in appearance.1 Figure 1 shows his Table of 1869. The elements are ordered on atomic weight with 'Groups' running horizontally, eg Li, Na, K, Rb and Cs. H stands alone. The elements In, Ce and Ur are positioned according to their wrong atomic weights; and there are gaps for the yet-to-be discovered elements with atomic weights of 45, 68 and 70. Here Mendeleev is certain. But he has problems with the heavy metals. Hg and Au are wrongly placed, as are Tl and Pb. It is the robust +1 and +2 oxidation states of these latter two elements that prompted him to put them below Cs and Ba respectively.
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