Diamond is hard and a bad conductor of electricity while graphite is soft and a good conductor of electricity..Explain state of hybridisation of carbon in both in both substance....

• Diamond each carbon is sp³ hybridized. Each carbon is surrounded by four other carbon atoms.The tetrahedra are linked together to form  a three dimensional molecule.The unit cell of diamond is cubic unit cell.This is because of this arrangment that diamond is very hard. Further there is no free electron in the carbon tetrahedra so that diamond do not conduct electricity.
• In graphite each carbin is sp² hybridized. Each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array.One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other.

Structure of graphite.

Due to this these layers can slip over each other so graphite has a slippery surface. Hence it is used as a lubricant.

Graphite is a good conductor of electricity. Its structure is the main reason for this property. Each carbon atom in graphite is directly linked to only three carbon atoms through covalent bonds. Therefore, out of the four valence electrons in a carbon atom, only three are used for bonding and the fourth is relatively free and can move from one carbon atom to the other. These free electrons make graphite a good conductor of electricity.