Discontinuous Change of Binding Type in the Series of Monohydrides. III. Regularities and Irregularities of Internuclear Distances and Force Constants

The recently attempted correlation of internuclear distances of the monohydrides of all elements by linear plots of logr vs logZ (atomic number) for each of the two octaves and of the three long periods is not satisfactory. The equations r(s)=2.2240 n(-0.426) and r(0)=2.7793 n(-0.371) (n is the total number of valence electrons in the hydride) apply merely from HF to BH and from HCl to AM, respectively. The marked deviations from these equations shown by the hydrides M (I) H and M (II) H are related to a discontinuous change of binding type. In the long periods, r increases for the hydrides of the heavy metals from M (I) H to M (III) H, due to the decrease of polarizability and penetrability of the cations with an 18-electron (s(2)p(8)d(10)) outer shell, e.g., from AgH to InH. It is emphasized that the knowledge of spectroscopic data for molecule ions of the hydrides of long period elements is necessary in order to decide at which places discontinuous changes of binding type occur.