8 Group IV
(Carbon, silicon, germanium, tin, lead)INTRODUCTION
SUMMARY OF GENERAL CHARACTERISTICS
In this group the outer quantum level has a full s level and two
electrons in the corresponding p level. As the size of the atom
increases the ionisation energy changes (see Table 8.1) and these
changes are reflected in the gradual change from a typical non-
metallic element, carbon, to the weakly metallic element, lead.
Hence the oxides of carbon and silicon are acidic whilst those of tin
and lead are amphoteric.
OXIDATION STATES
Gain of electrons
Only the carbon atom can gain four electrons; this only happens
when it is combined with extremely electropositive elements and
this state may be regarded as exceptional. Bonding in carbides is
almost invariably predominantly covalent.
Loss of electrons
The oxidation state -1-4 involves both the s and p electrons. The
oxidation state +2, involving only the p electrons, becomes in-
creasingly important with increasing atomic size, and the two .s
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