Interatomic Distances in Covalent Molecules and Resonance between Two or More Lewis Electronic Structures

In a paper to be published in the Zeitschrift für Kristallographie, Professor M. L. Huggins and I have formulated tables of radii for use in crystals containing electron-pair bonds. With the aid of these tables, we have also constructed a table of radii (table 1) for non-metallic atoms in covalent molecules. These radii are designed especially for purely covalent compounds, in which fluorine forms one electron-pair bond, oxygen two, nitrogen three, etc., but they are applicable also to other compounds, such as (CH3)3N:O:, with the following exception. The radii given for As, Se, Br, Sb, Te and I are to be used for these atoms with a covalence of one, two or three; for a covalence of four slightly smaller values ("tetrahedral radii") are to be used. The change is probably due to a change in the nature of the bond eigenfunctions involved.