Question

Is diamond an insulator?

Answer 1

Hint: An allotrope of carbon is a diamond. In a diamond, all the four electrons present in the outer shell on each carbon atom are used in covalent bonding, so there are no delocalised electrons present and thus makes the diamond an insulator.

Complete answer:
The substances that allow the flow of electric current (usually free electrons, move easily from atom to atom with the application of voltage) freely are known as conductors. In the case of diamonds, no free electrons are present to conduct electricity, as all 4 valence electrons of carbon atoms are used to create a bond with their neighbouring atoms.
The insulators neither conduct electricity nor heat. But, in the case of a diamond, an insulator, it is a good conductor of heat because of the presence of a strong covalent bond. This property of diamond is used in fields like jewellery making and by gemologists. If the diamond is heated over $$700{}^{\circ }C$$, in air, it gets oxidized, being a form of carbon.
$$\therefore$$The diamond is an insulator.

Additional information:
The other forms of diamonds, that is, the natural blue diamonds are not insulators, instead they are semiconductors, as the carbon atoms are replaced by the boron impurities. In the case of graphite, all the three electrons except one electron present in the outer shell on each carbon atom are used in covalent bonding, so one delocalized/valence electron will be present to conduct electricity and thus makes the graphite a conductor.

Note:
All the diamonds except the natural blue diamonds are insulators, because all the electrons form a covalent bond with the neighbouring atoms, whereas, in the case of graphite, except one, all the 3 electrons form a covalent bond with the neighbouring atoms, so, these free electrons conduct electricity.