Abstract
WHILE collecting together crystallographic data on the alkali metals, I noticed that the lattice constants for lithium, sodium, potassium, rubidium and caesium had all been determined at 5° K as well as at room temperature. These metals are isostructural, having the A2 structure; in other words, they are body centred cubic with two atoms per unit cell. The changes in atomic volume on cooling from room temperature to 5° K are plotted against the principal quantum number, n, of the outermost occupied shell in Fig. 1. It is seen that the relationship is linear. The volume changes, in A3, are closely reproduced by the equation Various speculators have failed to bring forth a theoretical reason for this linearity.
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