A-Level How atoms bond and how that governs a substance's behaviour: worked solution

Question

(h) Using ideas about structure and bonding, account for why the boiling point of N2O4 exceeds that of NO2.

N2O4 is the dimer of NO2, so it is a larger molecule with roughly twice as many electrons and a bigger electron cloud than NO2. The larger, more polarisable electron cloud produces stronger instantaneous dipole-induced dipole (van der Waals / dispersion) forces between N2O4 molecules than between NO2 molecules. More energy is therefore required to overcome the intermolecular forces in N2O4, so its boiling point is higher.