Intermolecular forces are usually composed of a repulsive and an attractive part:

• The repulsive part is essentially quantum mechanical (in particular, the Pauli exclusion principle plays a key role). However, often we approximate it by a hard-sphere infinitely steep potential, because the real potential is much steeper than other potentials in most problems.
• The attractive part shows more variability, but it almost invariably is of electrostatic origin.

If the potential indeed has an attractive component (the repulsive one always exists), then the potential will present a minimum, corresponding to an equilibrium state, known as a bond. The depth of the potential minimum (relative to the thermal energy, $k_B T$) determines the strength, or stiffness of the bond. One often makes a distinction between:

• Chemical bonds or permanent bonds (see here) are those with bond energy is much larger than the thermal energy.
• Physical bonds or temporary bonds are those with bond energy comparable to, or just a bit bigger than the thermal energy.

Common intermolecular forces

• Van der Waals forces.
• Hydrogen bonds.
• Hydrophobic interaction.

See this video, examples