Which intermolecular forces do I need to know about and how do they differ in strength?

The intermolecular forces you will need to know about are induced dipole-dipole, permanent dipole-dipole, and hydrogen bonding. Induced dipole-dipole interactions occur when there is only a small or no difference in electronegativity between atoms in a molecule. At any given time, one part of a molecule will have a higher electron density than the other due to random electron movement within orbitals. This causes one side of the molecule to be slightly negative and the other to be slightly positive. This instantaneous dipole causes an induced dipole in an adjacent molecule. Oxygen exhibits this form of intermolecular force.Permanent dipole-dipole interactions occur between polar molecules. Molecules are polar when the atoms which form them have a significant difference in electronegativity. When polar molecules are near each other, the slightly positive side of one molecule will be attracted to the slightly negative side of another. An example of a compound that exhibits this is hydrochloric acid. The final type of intermolecular force you will need to know about is hydrogen bonding, which is a specific example of permanent dipole-dipole interactions. It occurs when hydrogen is covalently bonded to either nitrogen, oxygen or fluorine. The slightly positive hydrogen is attracted to the slightly negative nitrogen, oxygen or fluorine of the adjacent molecule. Hydrogen bonding occurs between water molecules and is responsible for many of water's properties. Hydrogen bonds are the strongest intermolecular force, followed by permanent dipole-dipole, followed by induced dipole-dipole.