2.2.8—Intermolecular forces (IMF)

Force	Evidence used to identify it
London dispersion	Present; increases with molecular size and electron count
Dipole-induced dipole	A permanent dipole induces a dipole in a neighbour
Dipole-dipole	Permanent dipoles attract
Hydrogen bonding	Hydrogen bonded to a strongly electronegative atom creates the required interaction

Start with molecular size and polarity, then check for the structural requirement for hydrogen bonding. More than one IMF can be present.

All molecules have London dispersion forces. Add permanent dipole–dipole attraction when a net molecular dipole exists, and add hydrogen bonding only when the required H–N, H–O or H–F environment and an acceptor lone pair are present. Name every relevant force before deciding which dominates.

Representative question

[Maximum number: 2]

Outline how a hydrogen bond is formed.

Retrieve the covalent pathway: shared pairs and bond order lead to geometry, polarity and molecular polarity; structure determines network properties, IMF behaviour and chromatography; HL representations extend to resonance, formal charge, sigma/pi bonds and hybridization.

Check the representation first, then count domains, apply geometry, identify polarity or forces, and connect the structure to the requested property or HL bonding description.

2.2.8—Intermolecular forces (IMF)

Intermolecular Forces

Identifying IMFs

Assessment in practice

The Covalent Model Summary

Question 1