Additive covalent radii for single-, double-, and triple-bonded molecules and tetrahedrally bonded crystals: a summary.

The recent fits of additive covalent radii R(AB) = r(A) + r(B) for the title systems are reviewed and compared with alternative systems of radii by other authors or with further experimental data. The agreement of the predicted R with experiment is good, provided that the A-B bond is not too ionic, or the coordination numbers of the two atoms too different from the original input data, used in the fit. Bonds between transition metals and halides are not included in the single-bond set, because of their partial multiple-bond character.