London dispersion forces (LDF) are the weakest type of intermolecular force. They are a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles instantaneously.
LDF are the attractive forces that cause non-polar substances to condense to liquids and freeze into solids when the temperature is lowered sufficiently.
The magnitude of the force is affected by three factors:
- Number of electrons: the more electrons, the larger the distance between valence electrons and the nucleus. Thus, the electron cloud can be polarised more easily.
- Size and volume of electron cloud: the larger the cloud, the easier it can be polarised.
- Molecular shape: a large contact area results in a greater force magnitude.
Polarizability is the ease of distortion of the electron cloud of a molecular entity by an electric field. Every molecule will experience London forces, whether polar or non-polar.