Diamond is a very large molecule made up of carbon atoms. Numerous carbon atoms are attached to each other in a single bond. So it is an object with a three-dimensional network. In its molecule, each carbon atom is located at the center point of a tetrahedron made up of four other carbon atoms . Since the C - C bond is very strong and each carbon is attached to the other four carbons in such a strong bond , diamond is a very solid substance. Of all the substances actually obtained, it is the hardest. Lots of heat energy is needed to break C - C bonds. So its melting point is also very high (3960). Since the molecule has no circulating electrons, it is electrically conductive.