Although metallic and ionic solids have three-dimensional
structures, it does not follow that three-dimensional structures
are necessarily metallic or ionic. Diamond, for
example, is a non-metal (see Sections 5.11 and 5.12). In
Sections 1.12 and 1.15, we considered the inclusion of
ionic contributions to ‘covalent’ bonding pictures. Later in
this chapter we shall discuss how including some covalent
character in a predominantly ionic model comes closer to
reality for some so-called ‘ionic’ compounds.