In graphite, each carbon atom forms three covalent bonds with three other carbon atoms. This makes flat layers made of hexagonal rings of carbon atoms. There are no covalent bonds between the layers. The layers are held together only by weak forces, so they can slide over each other easily. This makes graphite soft and slippery, and it is used as a lubricant and in pencils.
Each carbon atom uses only three of its four outer electrons for bonding. The fourth electron from each atom is delocalised, which means it is free to move along the layer. These delocalised electrons can carry charge, so graphite conducts electricity. They can also carry thermal energy, so graphite conducts heat.
Graphite still has a very high melting point, because the covalent bonds within each layer are strong and a lot of energy is needed to break them. In this way graphite is similar to metals, which also have delocalised electrons and conduct electricity.
