The attractive forces that hold the molecules of a liquid together are always the result of opposite charges from the opposite ends of polar molecules, although that polarity is not always inherent to the molecules involved. Even the electrons of molecules, which are not polar, are in constant motion, and in the presence of another molecule, momentary induced dipoles can be created. These are much weaker than inherent dipoles, however.Continue Reading
The strongest forces of attraction between molecules in a liquid are called hydrogen bonds, which are only possible in compounds like water with strongly polar covalent bonds between hydrogen and an electronegative element such as oxygen. Because the bond is so highly polar, the hydrogen atoms in water get a very small proportion of the shared electrons in the bond. Thus, they are able to form a partial bond with nearby oxygen atoms that are also bonded to hydrogen, which almost resembles a covalent bond but is substantially weaker. The normal attraction between polar molecules tends to be less than the extremes allowed by hydrogen.
There are other types of liquids that do not contain any molecules, however, and so they cannot be said to have attractive forces between molecules. These are molten salts, which are held together by the opposite charges of their constituent ions rather than any polarity in neutral molecules.Learn more about Atoms & Molecules