A temporary (instantaneous) dipole is a short-lived dipole that forms when the electron cloud of a molecule happens, at a given instant, to be unevenly distributed. Because electrons are in constant motion, such momentary imbalances arise even in non-polar molecules. A temporary dipole can induce a dipole in a neighbour, which is the origin of London dispersion forces.

瞬时偶极是当分子的电子云在某一瞬间恰好分布不均时形成的短暂偶极。由于电子不停运动,即使在非极性分子中也会出现这种瞬间的不平衡。瞬时偶极可在邻近分子中诱导出偶极,这正是伦敦色散力的起源。