Unified structural classification of AB₂ molecules and solids from valence electron orbital radii

We present structural plots for AB2 molecules and solids with sp-bonding based on parameters derived from valence electron orbital radii. We show that the same schemes that allow one to classify crystals with different structures, are also able to distinguish molecular shapes into linear and bent. Our picture is consistent with the existence of a critical number Nc=16of valence electrons, in agreement with the Mulliken-Walsh rule, and accounts for many exceptions to the latter in the case N≤16. We discuss critically our findings and announce new results on AB3 molecules. We also discuss preliminary results of model calculations on AB2 molecules. © 1987 Springer-Verlag.