Intermolecular forces are electromagnetic forces which act between molecules. Listed in order of decreasing strength, these forces are:

Table of contents
1 Ionic Interactions
2 Hydrogen Bonding
3 Dipole-Dipole Interactions
4 London Dispersion Forces

Ionic Interactions

This is an interactions that occurs between charged species, like charges will have a repulsive force while opposite charges will have an attractive force.

Hydrogen Bonding

hydrogen bonding can be formed when a hydrogen atom is bound to a highly electronegative atom such as nitrogen, oxygen, or fluorine. The hydrogen atom has a partial positive charge and can interacts with another electronegative atoms found in a different molecule (again N, O, or F). This results in a stabilizing interaction that loosely binds the two molecules together. A common example is water:


Hydrogen bonds are found throughout nature. Hydrogen bonds give water its unique properties, which allowed life to develop on earth; hydrogen bonds are also the intermolecular force that binds together the two strands in a molecule of DNA

Dipole-Dipole Interactions

Dipole-Dipole interactions are the forces that occur between two molecules with permanent dipoles. These work in a similar manner to ionic interactions but are weaker because only partial charges are involved. An example of this can be seen in hydrochloric acid:

(+)(-)    (+) (-)

London Dispersion Forces

Also called London forces or Van der Waals forces, these involve the attraction between temporaily induced dipoles in nonpolar molecules. This polarization can be induced either by a polar molecule or by the repulsion of negatively charged electron clouds in nonpolar molecules. An example of the former is chlorine dissolving in water:

                 (+)(-)(+)  (-) (+)
[Permanent Dipole] H-O-H-----Cl-Cl [Induced Dipole]

An example of the second scenario is found in molecular chlorine:

               (+) (-)    (+) (-)
[Induced Dipole]Cl-Cl------Cl-Cl [Induced Dipole]