London Dispersion Forces
Attractions between molecules caused by instantaneous fluctuations in electron distribution inducing dipoles in neighbours.
Formula / equation
E ∝ α² / r⁶
Unit
kJ/mol
In depth
Present in all matter and the only force acting between non-polar species, dispersion forces strengthen with polarisability and with molecular surface area. This is why boiling point climbs down a group and why straight-chain alkanes boil higher than their branched isomers of the same formula.
Examples in the real world
Pentane boils at 36 °C but neopentane at only 10 °C; iodine is solid while fluorine is a gas.