When do intermolecular forces of attraction occur?
Intermolecular forces occur whenever two particles come close to each other.
Intermolecular forces between molecules include hydrogen bonds and dipole-dipole attractions. Dipole-induced dipole forces and London dispersion forces are weaker forces.
If ions are present, we can have ion-ion, ion-dipole, and ion-induced dipole attractions.
Some of these forces are stronger than others. Some of them decrease more rapidly with increasing distance.
Even so, the forces that can occur will always occur when the particles are close enough.