The intermolecular forces involved in molecular crystals are as follows :

(1) Weak dipole-dipole interactions : The solids constituting polar molecules like HCl, H₂O, SO₂, etc. which possess permanent dipole moment involve weak dipole-dipole interactions.

(2) Very weak dispersion or London forces : The solids consisting of nonpolar molecules like CH₄,H₂, etc. involve weak dispersion forces. They are also involved in monoatomic solids like Ar, Ne.

(3) Intermolecular Hydrogen bonds :

• In this crystalline solids, the constituent particles are the molecules which contain hydrogen atom linked to highly electronegative atom like F,O or N.
• In these, molecules are held by hydrogen bonds in which H atom of one molecule is bonded to electronegative atom (like F, N or O) of another molecule.
• Since hydrogen bonding is weak, these solids have very low melting points and generally at room temperature they exist in the liquid or gaseous state.
•  They are non-conductors of electricity.