Inorganic chemistry valence orbitals

In books on inorganic chemistry, the marked increase in the stability of the lower oxidation state (by two units) of heavier elements descending the main groups of the periodic Table is often explained by the inert s-pair effect (see J. E. Huheey U)). For example, elements like In and Sn may use only 1 or 2 electrons for the formation of bonds instead of 3 or 4 (group number), leaving one electron pair in the outer valence shell inert . The electron pair is assumed to occupy an s-orbital. This classification does not very much contribute to the understanding of bonding first... 

Among the countless concepts that Linus Pauling introduced from Quantum Mechanics into chemistry[l,2], and that became standard principles of the trade, there is the idea of hybridization . In the framework of the valence-bond description of a system, it is useful to mix atomic orbitals of the same n-quantum number , or of similar spatial extent, to construct directed, asymmetric atomic contributions. Although hybrids are not needed in an LCAO-MO description of the system, they have so much become part of the language of both organic and inorganic chemistry, that people will go out of their way to arrive at descriptions that are compatible with them. 

The valence bond model and the accompanying idea of orbital hybridization have applications beyond those of bonding in hydrocarbons. A very simple extension to inorganic chemistry describes the bonding to the nitrogen of ammonia and the oxygen of water. 

Chapter 10. The Molecular Orbital Valence Bond Theory of Inorganic Chemistry. 

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