Valency, concept

The earlier derivation (22) of Eqn. II.2 was based on classic valence concepts, although these had clearly been influenced by quantum-chemical ideas. Even within the classic approach, a critical reexaimina-tion of the underlying assumptions is valuable in order to establish what is the minimum number needed to deduce Eqn. II.2. 

Where both interpretations were found to be inappropriate, the classic valence concept was reformulated, either by taking a different value for Ni (e.g. the idea of expanded octets) or by reclassifying certain A1 atoms as cationic constituents in particular cases. 

Our principal goal has been to translate the deepest truths of the Schrodinger equation into a visualizable, intuitive form that makes sense even for beginning students, and can help chemistry teachers to present bonding and valency concepts in a manner more consistent with modern chemical research. Chemistry teachers will find here a rather wide selection of elementary topics discussed from a high-level viewpoint. The book includes a considerable amount of previously unpublished material that we believe to be of broad pedagogical interest, such as the novel Lewis-like picture of transition-metal bonding presented in Chapter 4. 

The loss of outer electrons from the atoms to a conduction band, in such a simple picture, bears a similarity to the redox process which is supposed to occur in molecular bonds, and which is at the basis of the oxidation state or formal valence concept. If this is the case, the metallic valence should coincide with one of the valences that one encounters in compounds, possibly with the most stable one. 

It is clear that the difference between the two effects in not clearcut. In fact, one may even doubt whether in the case of strong itineracy of 5 f s, the metallic valence concept retains any usefulness at all. 

Steiner, Th. (1995a). Lengthening of the N-H bond in N-H... N hydrogen bonds. Preliminary structural data and implications of the bond valence concept. Chem. Comm. 1331-2. 

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