| Themes > Science > Chemistry > Inorganic Chemistry > More Information about Chemical Bonding > More About Bonding > Forces Between Nonpolar Molecules |
What keeps together nonpolar molecules? Even though nonpolar molecules have dipoles that cancel each other out, there are points where the electrons may not be evenly distributed (i.e. in different locations). At this instant the atom would have a momentary dipole. For example, N2, a nonpolar molecule, forms a liquid at very low temperatures. The N2 molecule is attracted for a very short time to another N2 molecule result in a very weak, but present intermolecular attraction. This temporary attraction are called London forces. London forces account for the fact that nonpolar molecules can form liquids and solids at low temperatures. However, these forces are only one tenth of the strength of dipole-dipole force. These forces can increase when more electrons and larger molecules are present. For example, methane can form a liquid at a higher temperature that N2, but compared to H20, its boiling point is very low. Due to their weak London forces, N2 and CH4 tend to be gases at room temperature, while H20 is a liquid at the same temperature. Dipole-dipole forces and London forces can be considered together and are know as van der Waals forces (name for a scientist who proposed and study their existence). In general, polar molecules tend to have stronger intermolecular bonds than nonpolar molecules. This can lead to a huge difference in the boiling points of polar and nonpolar molecules of similar atomic masses. The polar molecule would have a higher boiling point. |
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