Question

Diamond is a covalent solid, yet has a high melting point, Why?

Answer 1

Hint: To understand the properties of diamond, draw the structure of atoms present in diamond. Identify the hybridisation. Diamond being an allotrope of carbon has catenation property. The interlinking of carbon atoms can help you to understand why diamond has a high melting point.

Complete step by step answer:
Diamond is a solid form of carbon element with its atoms arranged in a crystal lattice called diamond cubic. At room temperature and pressure, carbon exists in another solid form called graphite which is the stable form chemically.

Although graphite is the stable form, diamond almost never converts to graphite form. Diamond has the highest hardest and characteristic thermal conductivity of any material. This property is used for cutting and polishing tools.

Diamond is a covalent solid and yet has a high melting point mainly due to its interlinked structure. Diamond crystallises in a lattice structure, indicating the presence of strong covalent bonds.
Diamond has a characteristic 3D network in which one carbon is bonded to 4 carbon atoms i.e. having $\text{s}{{\text{p}}^{\text{3}}}$ hybridisation. This network between carbon atoms is the reason why diamond has a high melting point unlike other covalent solids.

Note: Graphite which is also an allotrope of carbon is a good conductor of electricity and heat. Carbon atoms in graphite are attached to only 3 carbon atoms unlike 4 in diamond. Due to this carbon atoms have a free electron. These free electrons are present in sheets of graphite and help in conduction of electricity.