Intermolecular forces
London (instantaneous dipole–induced dipole) forces exist between all molecules; they grow with the number of electrons and surface area. Permanent dipole–dipole forces act between polar molecules. Hydrogen bonds form when H is bonded to N, O or F and is attracted to a lone pair on N, O or F of another molecule; they are the strongest intermolecular force. Hydrogen bonding explains the high boiling point of water, NH₃ and HF, and why ice is less dense than water. Stronger intermolecular forces mean higher boiling points.
≈ 40 min