Stoichiometric Valence and Structural Valence—Two Different Sides of the Same Coin: “Bonding Power”

Two valencies instead of one! Stoichiometric valence and structural valence are two distinct properties of atoms. The former, stoich V , is derived from the composition of a compound and has integer values; the latter, struct V , depends on the structure of a compound and has non‐integer values. The scheme shows a representation of valence states of antimony and oxidation of Sb III to Sb V , as a function of the eccentricity parameter Φ i .Recent studies use the term valence to describe two distinct aspects of the phenomenon bonding power of an atom. Measured in valence units, one valence term, the classical chemical valence, has integer values and is derived solely from the composition of a compound. The second one, used mainly by solid‐state physicists and crystallographers, has non‐integer values. It is determined from structure data, which are derived from diffraction experiments, spectroscopy, or quantum‐chemical calculations. To distinguish clearly between these two types of valencies, the descriptive terms stoichiometric valence and structural valence and the respective symbols stoich V and struct V should be used. For the majority of crystalline structures, values of stoich V and struct V , both measured in valence units, differ by less than 5 %. However, for p‐block atoms with one lone electron pair, differences between stoich V and struct V of up to 30 % have been reported.