soft and conducts electricity. It is composed of flat two dimensional sheets of carbon atoms. Each sheet is a hexagonal net of sp hybridised carbon atoms with a C-C bond length of . Å which is close to the Figure .
Structure of graphite - - - - C-C bond distance in benzene ( . Å). Each carbon atom forms three σ bonds with three neighbouring carbon atoms using three of its valence electrons and the fourth electron present in the unhybridised p orbital forms a π-bond. These π electrons are delocalised over the entire sheet which is responsible for its electrical conductivity.
The successive carbon sheets are held together by weak vander Waals forces. The distance between successive sheets is . Å. It is used as a lubricant either on its own or as a graphited oil.
Unlike graphite the other allotrope diamond is very hard. The carbon atoms in diamond are sp hybridised and bonded to four neighbouring carbon atoms by σ bonds with a C-C bond length of . Å. This results in a tetrahedral arrangement around each carbon atom that extends to the entire lattice as shown in figure .
. Since all four valance electrons of carbon are involved in bonding there is no free electrons for conductivity. Being the hardest element, it used for sharpening hard tools, cutting glasses, making bores and rock drilling. Fullerenes are newly synthesised allotropes of carbon.
Unlike graphite and diamond, these allotropes are discrete molecules such as C , C , C , C , C etc.. These molecules have cage like structures as shown in the figure. The C molecules have a soccer ball like structure and is called buckminster fullerene or buckyballs. It has a fused ring structure consists of six membered rings and five membered rings.
Each carbon atom is sp hybridised and forms three σ bonds & a delocalised π bond giving aromatic character to these molecules. The C-C bond distance is . Å and C=C distance . Å.
Carbon nanotubes,