Non-metals are elements that generally cannot conduct electricity. They are the second-largest class of elements after metals. Carbon is the only non-metal which conducts electricity. It is classified as a semi-metal when it is in the form of graphite. In a graphite molecule, one valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas in diamond, they have no free mobile electron. Hence, there won’t be a flow of electrons That is the reason behind the diamond is bad conductor electricity.