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Attractions between molecules are called intermolecular forces. Intermolecular forces hold two or more molecules together. These are contrary to intramolecular forces. Intermolecular forces may also be called intermolecular attractions.
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Intermolecular forces must exist between all molecules because all gases condense to liquids if the temperature is low enough and the pressure is high enough. Intermolecular forces are often called van der Waals forces. Intermolecular forces are not nearly as strong as intramolecular forces. The energies required to break covalent bonds ordinarily range from 150 to 800 kJ/mol, whereas the energies required to overcome intermolecular forces are normally of the order of 1−10 kJ/mol. The strength of intermolecular forces decreases rapidly with increasing distance between molecules. Therefore, intermolecular attractions are not very important with respect to gases, but are very important with respect to liquids and solids. There are two kinds of intermolecular force: dipole−dipole interactions and London (dispersion) forces. "Hydrogen bonds" result from unusually strong dipole−dipole attractions.
The nature of the attractive forces between molecules should be first understood before considering how the kinetic-molecular theory explains the properties of liquids and solids in more detail.
Related
▪ L - Intramolecular Forces
▪ L - Intermolecular Potential Energy