Modern inorganic chemistry

26 STRUCTURE AND BONDING

is generally true to say that each atom is surrounded by as many

neighbouring atoms as can be accommodated in the space available.

There are no directed forces between the atoms and each atom

'attracts' as many similar atoms as can be accommodated. The ease

with which metals conduct electricity indicates that the electrons are

only loosely held in this type of structure.

THE GIANT MOLECULE LATTICE

This is a relatively rare structure, diamond being probably the best

known example. Here, the carbon atoms are not close-packed. Each

carbon is surrounded tetrahedrally by four other carbon atoms

(Figure 2.1). Clearly, each carbon is exerting a tetrahedrally directed

Figure 2.1. Structure of diamond

force on its neighbours and such directed forces are operative

throughout the whole crystal Diamond is found to be a refractory

solid, i.e. it has an extremely high melting point, indicating that the

bonding forces are extremely strong. Boron nitride (BN)n and

silicon carbide (SiC)n (carborundum) are similar types of solid.

These solids are non-conducting, indicating that the electrons are

less free and more localised than the electrons in a metal which

move easily allowing an electric current to flow through the lattice.

THE GIANT IONIC LATTICE

This is one of the most familiar types of structure in inorganic
chemistry. The crystals can usually be melted in the laboratory