Why can graphite conduct electricity?

• A. It contains delocalised electrons which are free to move
• B. It has a three-dimensional network of covalent bonds
• C. It is made of ionic compounds
• D. It has electrons fixed in bonds

Answer: (A)

Graphite conducts electricity because its carbon atoms form planar layers with each carbon using three of its outer electrons for bonds. The fourth electron from each carbon becomes delocalised, spreading over the layer as part of a pi electron system. These delocalised electrons are free to move within the plane, so when a potential difference is applied they carry charge and enable electrical current to flow. The layers are held together by weak van der Waals forces, so conduction mainly occurs within the layers rather than between them. This contrasts with a three-dimensional covalent network like diamond, where electrons are tied up in fixed bonds and can’t move, or with ionic compounds, which only conduct electricity when melted or dissolved. Electrons fixed in bonds can’t move to carry charge, so they don’t explain graphite’s conductivity.