Graphite exists as black, slippery, hexagonal crystals. The carbon atoms in graphite, form flat layers, and are joined together by strong covalent bonds. These layers are arranged in parallel, one above the other, with weak intermolecular forces operating in-between the layers. These weak forces allow movement of the plane parallel over each other.
Graphite occurs in nature. It is also produced industrially by heating coke to a high temperature, in an electric furnace. This process is called the Acheson process.
Properties of Graphite
- Graphite is an opaque, flaky, soft crystalline solid with metallic lustre.
- It is chemically inert and has a high melting point, but less dense than diamond.
- Unlike diamond, graphite is a good conductor of heat and electricity because of the presence of mobile electrons in the crystal lattice.
- The mobile electrons exist since only of three out of the four valence electrons of each carbon atom in the graphite, are involved in bond formation, while the fourth electron is delocalised and free to move within the structure.
Uses of Graphite
- Graphite is used as a lubricant in engines, where high temperatures melt ordinary lubricant. This is because graphite is non-volatile and non-sticky.
- A mixture of graphite and clay is used in the manufacture of lead pencils.
- As a good conductor of electricity, graphite is used as electrodes in electrolytes.
- It is used to line crucibles used for making high-grade steel and in the coating of irons.
- Graphite is used as a black pigment in paints and as a neutron moderator in atomic piles.
The main differences in the properties of the two allotropes are summarised in the table below.