What are intermolecular forces?
They are dipole-dipole forces, hydrogen bonds, and London dispersion forces.
Two nearby polar molecules arrange themselves so that the negative and positive ends line up. An attractive force holds the two molecules together
The H atom in an O-H, N-H, or F-H bond has a partial positive charge. The N, O, or F atoms in a neighbouring molecule have a partial positive charge.
The dipole-dipole attractions between these charges are hydrogen bonds. Water molecules have strong H-bonds.
LONDON DISPERSION FORCES
At any given instant, there may be a greater electron density on one end of a nonpolar molecule than on the other. This instantaneous dipole can induce a dipole in a neighbouring molecule. This causes a weak attractive force called a London Dispersion Force.