London Forces
Definition and meaning of London Forces in chemistry.
London forces are weak, temporary intermolecular attractions that occur between all atoms and molecules as a result of the continuous motion of electrons in electron clouds.
In more detail
Also known as London dispersion forces, these interactions are caused by the formation of instantaneous dipoles when electron distribution becomes momentarily asymmetrical around a nucleus. This temporary dipole induces a corresponding temporary dipole in an adjacent atom or molecule, resulting in a weak electrostatic attraction between the two species. London forces are the only type of intermolecular force present in nonpolar molecules and noble gases. The strength of these dispersion forces increases with the polarizability and surface area of the molecule, which is why larger halogens and longer-chain alkanes have higher boiling points.
Key facts
| Field | General Chemistry |
|---|---|
| Cause | Instantaneous dipoles |
| Strength Factor | Polarizability |
London forces are responsible for allowing nonpolar halogens like iodine (I2) to exist as a solid at room temperature, due to iodine's large, highly polarizable electron cloud creating relatively strong dispersion interactions.
Frequently asked questions
Are London forces present in polar molecules?
Yes, London forces are present in all molecules, but in highly polar molecules, their effects are often overshadowed by stronger dipole-dipole interactions or hydrogen bonding.
Why do larger atoms have stronger London forces?
Larger atoms have valence electrons that are further from the nucleus, making their electron clouds more polarizable.