Lewis highly covalent oxides

The reactions (both dissociative and nondissociative adsorption of water) are highly exothermic and their equilibrium is shifted toward left by heating and lowering water vapor partial pressure. On the other hand, at least for ionic oxides, it is clear that bases stronger than water can also displace water from Lewis sites. This has been found, for example, for ammonia [128]. Consequently, the number of Lewis acid sites actually available depends on the degree of dehydroxylation of the surface that depends primarily on the temperature, on the composition of the environment and on the ionicity-covalency of the oxide (Scheme 9.2). 

These conventions make the oxidation numbers highly tributary of Lewis schemes, which fix the assignment of electrons of the bounds in covalent compounds. Two cases must be considered ... 

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