Temporary Dipoles

Non-polar molecules can form temporary dipoles. These dipoles come and go (are not permanent), but do allow for intermolecular bonding. The frequency of these bonds help us explain characteristics like solubility, melting point and boiling point (and sublimation point for iodine and carbon dioxide).

Temporary dipoles are more likely to form in molecules with large electron clouds. This is hard to infer quickly, so we use relative molar mass (M_R) to infer the size of the electron cloud. Molecules with larger M_R will usually have larger electron clouds.

The intermolecular bond between neighbouring non-polar molecules is called a "temporary dipole-temporary dipole force". It is usually due to an instantaneous dipole in one molecule and an induced dipole in the other molecule.

The intermolecular bond between a polar molecule and a non-polar molecule is called a "permanent dipole-temporary dipole force". It is due to a permanent dipole in one molecule (the polar molecule) and an induced dipole in the other molecule. (the non-polar molecule).