Structure of carbon and Graphite

Structure of carbon and Graphite 

            Diamond and graphite are two crystalline allotropic forms of carbon. Some of the important properties of these are:

(i)                   Diamond is denser than graphite. The density of diamond is 3.514 g cm–3 while that of graphite is 2.226 g cm–3.

(ii)                  Diamond is hard while graphite is soft. Graphite has lubricating properties. On the other hand, diamond is the hardest substance known.

(iii)                 Diamond is a bad conductor of electricity while graphite is a good conductor of electricity.

(iv)                 Diamond id extremely chemically unreactive whereas graphite is quite reactive.

The different properties of diamond and graphite can be easily explained on the basic of their structures as described below:

Structure of diamond

Diamond has a network structure consisting of a very large number of carbon atoms bonded to each other. Each carbon atom is sp3 hybrilised and is show in fig. 13.7(a). It is clear from the figure that each carbon atom lies at the centre of a regular tetrahedron and the other four carbon atoms are equal to 154 pm. Therefore, there is a three-dimensional network of strong covalent bonds in diamond. This makes diamond an extremely hard crystal with very high melting point (3843 K).

Since all the valance electrons of carbon are strongly held in carbon-carbon bonds, diamond is a poor conductor of electricity.