London dispersion force

A weak intermolecular attraction caused by correlated fluctuations in electron distributions that create instantaneous and induced dipoles. It occurs between all atoms and molecules, including nonpolar ones.

Instantaneous dipole: A temporary separation of charge produced by an uneven electron distribution in an atom or molecule. Electron fluctuations create the temporary dipoles that initiate dispersion attraction.
Electron cloud: The region around an atomic nucleus in which an electron is likely to be found. Its changing shape and density generate instantaneous dipoles.
Boiling point: The temperature at which a liquid’s vapor pressure equals the surrounding pressure. Stronger dispersion generally raises the energy needed to separate molecules into vapor.
Dipole–dipole interaction: An attraction between permanent dipoles whose positive and negative ends align favorably. Unlike this interaction, dispersion does not require permanent molecular dipoles.
Fritz London: A German-born theoretical physicist whose work helped establish the quantum theory of chemical bonding and intermolecular forces. London gave the first quantum-mechanical account of this attraction in 1930.
Induced dipole: A temporary charge separation caused when a nearby electric field distorts an atom’s or molecule’s electron distribution. An instantaneous dipole polarizes a neighbor, producing the paired dipole in dispersion.
Dipole moment: A vector measure of the separation of positive and negative charge in a system. Temporary dipole moments describe the charge separations involved in dispersion.
Viscosity: A fluid’s resistance to flow under an applied force. Dispersion contributes to cohesive attractions that can increase liquid viscosity.
Hydrogen bond: A directional attraction involving hydrogen bonded to an electronegative atom and another electron-rich site. Hydrogen bonding has specific structural requirements absent from dispersion.
London equation: A quantum-mechanical expression describing the attractive interaction between two induced dipoles at long range. It quantifies the distance dependence and strength of the force in a simple model.

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