Why is graphite a good conductor of heat even though it's a non metal?

Graphite is a good conductor of heat because it has electrons that can move freely about the molecule.

Graphite is a good conductor of heat because it has electrons that can move freely about the molecule.

Graphite is composed of pure carbon in which the atoms are situated in layers, as in Figure A, below.

Graphite conducts heat in two ways.

By movement of electrons

The electrons are free to move along the layers, like the electrons in the π orbitals in benzene — the pink orbitals in Figure B, above.

This movement of electrons allows the electrons to travel from one end of a sheet to the other.

These moving electrons can carry the heat energy across the molecule.

Through vibrations of bonds

If you apply heat at one end of a sheet, the bonds vibrate more vigorously.

This kinetic energy of vibration is transmitted to nearby bonds and to the other end of the sheet.

Graphite is a good conductor along a sheet, but a poor conductor from one sheet to another.

Diamond is a good conductor of heat but a poor conductor of electricity.

In diamond, the carbon atoms are joined by covalent bonds into a strong crystal lattice.

The electrons are not free to move, but bond vibrations are easily transmitted in all directions throughout the crystal.

Diamond is a great electrical insulator, but it conducts heat better than copper.