London Dispersion Attraction

1. Even when atoms are sharing electrons equally, the electrons are not static objects. They are constantly in motion. Sometimes due to their random movement between the two atoms in covalent bond they just happen to be more on one side than another.
2. A fleeting instantaneous dipole (region of positive and negative charge) can be formed by the random distribution of electrons at any particular moment.
3. This instantaneous dipole can induce a dipole in another nearby non-polar molecule. They can then attract to each other in a similar way as the dipole-dipole attraction. However, the London dispersion force is much weaker than a dipole-dipole attraction.
4. The visualization below, used with permission, came from the Colby College chemistry department and was created by Thomas Poon and Bradford Mundy.
5. The size of a molecule can affect the London dispersion force between two molecules. The more surface area there is on a molecule the greater chance there will be at least one instantaneous dipole at any particular moment. Therefore, the greater the surface area (generally this means the bigger the molecule) the stronger the attraction between two molecules of this type due to London dispersion forces

   Name	Propane	Butane	Pentane
   Boiling Point	-42°C	0°C	36°C
   Structural Formula
   Surface Charges	Toggle Transparency	Toggle Transparency	Toggle Transparency

   ---

   previous page

   chemsite homepage