A Re-Evaluation of the Covalent Radii of Some of the Elements

Abstract

The Schomaker‐Stevenson correction for ionic character, —β|x_A—x_B|, of the covalent radii additivity rule, d_AB = r_A+r_B, is extended to double bonds. The value of the parameter β found for these is 0.06. Several revisions in the table of covalent radii are proposed. The double‐bond covalent radii of oxygen and nitrogen are chosen as 0.604A and 0.62A, respectively, or one‐half the bond lengths of O₂ and of the ^–N=N_– length in azomethane. The single‐ and double‐bond covalent radii of carbon are revised upward to 0.79A and 0.675A to make them in accord with the lengths predicted by Mulliken, Rieke, and Brown for ideal single and double CC bonds. The newly assigned values are shown to be consistent with double bonds formed between unlike atoms when the shortening caused by ionic character is taken into account. Some other covalent radii are determined by extrapolation of curves determined by the known radii and by application of the revised additivity rule.