Letter | Published:

Atoms and Electrons


On the basis of any theory of atomic structure which classifies the elements according to rare gas type, cerium and thorium should be comparable with one another, since the atoms of each are possessed of four electrons more than those of the corresponding inert gases, xenon and niton respectively. There are, however, in the thorium atom, thirty-two more extra-nuclear electrons than in the cerium atom. In spite of this fact, it appears that the distances between atomic centres in crystals of these elements are practically the same (Ce = 3.62 A.U. andTh = 3.56 A.U., according to Hull), the distance being, if anything, slightly the smaller for thorium. Both crystallise in the face centred cubic lattice. If the interatomic distances may be taken as representing atomic diameters, this means that in the same (or slightly less) volume there are concentrated in the thorium atom thirty-two more electrons than in the cerium atom, the total numbers in the two cases being, respectively, ninety and fifty-eight.

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