States of Matter - Intermolecular Forces

Dispersion (or London) forces, dipole-dipole forces (including hydrogen bonds), and dipole-induced dipole forces

Electrostatic forces (as between ions) or covalent bonds holding a molecule together

Attractive intermolecular forces

An attractive force between an ion and a dipole. These are not considered as van der waal's forces, as the intent of classifying van der waal's forces was to identify forces between molecules of the same type.

Temporary dipoles formed in otherwise nonpolar molecules or atoms. Caused by a temporary unsymmetrical electrical charge inducing a dipole on a neighboring atom or molecule. Also called dispersion force. These forces are always attractive.

Interaction energy proportional to 1/r^6, range ~ 500 pm. Magnitude depends on the polarisability of the atom or molecules.

Between molecules w/ permanent dipole. Partial charges at the ends always less than unit electronic charge.

Solids typically have stationary polar molecules, with i.e. varying 1/r^3, while rotating polar molecules vary 1/r^6.

Intermolecular dipole-dipole attractions between ICl molecules are sufficient to cause them to form a solid at 0^oC, whereas the intermolecular attractions between nonpolar Br₂ molecules are not. (from /gchelp/liquids/dipdip.html)