Chemistry: The Effects of Intermolecular Forces

The Effects of Intermolecular Forces

The intermolecular forces present in a compound play a role in that compound's properties. This isn't really surprising when you think about it. After all, if the molecules in one liquid are held tightly together by a strong intermolecular force, this liquid would be expected to behave differently than a second liquid in which the molecules are held together very weakly. The following are two of the ways in which intermolecular forces affect the properties of a liquid:

• Melting and boiling point: Generally, compounds that undergo hydrogen bonding melt and boil at higher temperatures than compounds that experience dipole-dipole forces or London dispersion forces. For example, let's consider the following three molecules.
• Surface tension: Liquids with stronger intermolecular forces tend to have higher surface tension than those with weak intermolecular forces. For example, if you pour a very small amount of water on a table, it will tend to collect together in one large drop. On the other hand, if you do the same thing with lighter fluid, which has weaker intermolecular forces, you'd find that the lighter fluid tends to spread out over a larger area. For those of you who were planning on pouring lighter fluid on your coffee tables, please only do so under the supervision of a grown-up!

Compound	Intermolecular Force	Melting Point	Boiling Point
CH4	London dispersion force	-182º C	-164º C
HCl	Dipole-dipole	-115º C	-85º C
H2O	Hydrogen bonding	0º C	100º C