What forces are involved in chromatography?

The four forces involved in chromatography are the London dispersion, dipole-dipole, hydrogen bonding and ion-dipole forces.

• London Dispersion Force – This is a temporary attractive force that is caused when electrons in two adjacent atoms are displaced in such a way that the atoms form temporary dipoles. These intermolecular forces occur between nonpolar substances and cause them to condense to liquids and freeze to solids when the temperature is sufficiently lowered. The London dispersion force is the weakest of all intermolecular forces.
• Dipole-Dipole Force – This refers to the attractive force between the negative end of one polar molecule and the positive end of another polar molecule, in other words between two dipoles. It is a relatively weak force and has a significant effect only when the relevant molecules are in close proximity or touching one another. Dipole-dipole interactions can only occur between molecules such as H2O or HCl which possess permanent dipoles
• Hydrogen Bonding Force – This is a special class of dipole-dipole attraction between molecules that results in the formation of Hydrogen bonds. It is caused by the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as O, N, or F atom and another highly electronegative atom which lies in the vicinity of the hydrogen atom.
• Ion-Dipole Force – An ion-dipole force occurs between a partially charged dipole and a fully charged ion. The strength of the ion-dipole force is directly proportional to the ion charge. This force most commonly occurs in solutions.