Because each C atom of graphene is sp2 hybridized, it also contributes a carbon atom to the PZ orbital to form a large bond. Graphene has an empty conduction band and a full valence band. The bottom of the conduction band intersects the top of the valence band at the Fermi energy level, while the K point is at the Fermi energy level. Therefore, single-layer graphene tends to show metallic properties