On the crystal chemistry of normal valence compounds

A new classification of the crystal structures of normal valence compounds with simple atomic ratios is discussed.This classification is based on two atomic parameters which gauge the directional properties of the bonds in a compound.The parameters are (1) the average principal quantum number, ~, of the valence shell of the component atoms and (2) the difference,/lx, between the electronegativities of anion and cation.It is shown that the most common structures of compounds of composition AiX 1 (i, j = 1, 2, 3) occur only in certain well defined regions of a ~ versus ~Ix diagram, and the proposed classification, therefore, is of considerable help in understanding and predicting the structures of normal valence compounds.