Modern inorganic chemistry

162 GROUP IV

electrons are retained as an inert pair. There are no stable com-

pounds of carbon and silicon in this + 2 oxidation state; it is

uncommon (and strongly reducing) in germanium, less strongly

reducing and commonly found in tin and it is the most stable

oxidation state for lead. Only tin and lead are capable of forming

+ 2 ions which occur both in the solid state and in solution, where

the ions are stabilised by solvation.

The oxidation state +4 is predominantly covalent and the

stability of compounds with this oxidation state generally decreases

with increasing atomic size (Figure 8.1). It is the most stable oxida-

tion state for silicon, germanium and tin, but for lead the oxidation

state +4 is found to be less stable than oxidation state + 2 and

hence lead(IV) compounds have oxidising properties (for example,

seep. 194).

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Atomic number
Pb
Figure 8.1. Mean thermae hemical bond energies for representative bonds in Group IV
compounds
The concept of oxidation states is best applied only to germanium,
tin and lead, for the chemistry of carbon and silicon is almost
wholly defined in terms of covalency with the carbon and silicon
atoms sharing all their four outer quantum level electrons. These
are often tetrahedrally arranged around the central atom. There are
compounds of carbon in which the valency appears to be less than