They are covalent compounds.
1. The melting point is low due to the weak Vander Waal’s forces of attractions between the covalent molecules.
2. The force of attraction between the molecules of a covalent compound is very weak.
3. Only a small amount of heat energy is required to break these weak molecular forces, due to which covalent compounds have low melting points and low boiling points.
4. Please note that some of the covalent solids like diamond and graphite have, however very high melting points and boiling points.
