Question

What is an attraction between molecules of different substances?

Answer 1

A chemical bond is a long-term attraction between atoms, ions, or molecules that allows chemical compounds to form. Ionic bonds are formed by the electrostatic force of attraction between oppositely charged ions, while covalent bonds are formed by the sharing of electrons.

Complete answer:
Momentary dipoles arise in molecules due to the spontaneous unequal distribution of electrons, resulting in dispersion forces such as Van der Waals forces. This implies that the density of electrons on one side of the molecule will be higher than on the other at any given time (of course these averages out over the longer term). This causes an unequal charge distribution, which causes nearby molecules to have a similar effect, and the molecules can interact, but weakly.
Low melting solids, liquids, and gases at room temperature are examples of substances that depend on dispersion forces.
A hydrogen bond is formed when a hydrogen atom is bound to an atom that is both small and electronegative in a molecule (For the most part, this means $F,\,O\,or\,N$). The bond between these atoms becomes very polar as a result, and the $H$ atom becomes quite positive.
The ${\text{H}}$ would then be highly attracted to another molecule with a similar ${\text{F}}\,{\text{,}}\,{\text{O}}\,{\text{,}}\,{\text{or}}\,{\text{N}}$atom (due to the resulting partial negative charge on this atom). The strength of a hydrogen bond is usually one-tenth that of a covalent bond. It's the process by which the bases in a DNA molecule bind together (as one example).
Dispersion forces and hydrogen bonding are two of the most prominent ones.

Note:
Van der Waals forces, which include dipole-dipole forces and dispersion forces, are the weakest intermolecular forces. Hydrogen bonding is a form of dipole-dipole attraction that occurs between molecules rather than a covalent bond with a hydrogen atom.