may 1, 1908 - Changes to the periodic table P3

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In 1905, Swiss chemist Alfred Werner resolved the dead zone of Mendeleev's table. He determined that the rare-earth elements , 13 of which were known, lay within that gap. Mendeleev could not fit them in his table by 1901.
Combined with the lack of a known group of similar elements, this rendered the placement of the lanthanides in the periodic table difficult.This discovery led to a restructuring of the table and the first appearance of the 32-column form

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