The nature of this attractive force in molecules, which requires quantum mechanics for its correct description, was first recognized (1930) by the Polish-born physicist Fritz London, who traced it to electron motion within molecules. Third, even though no molecules of a material are permanent dipoles (e.g., in the noble gas argon or the organic liquid benzene), a force of attraction exists between the molecules, accounting for condensing to the liquid state at sufficiently low temperatures. An additional attractive force results from the interaction of a permanent dipole with a neighbouring induced dipole. Second, the presence of molecules that are permanent dipoles temporarily distorts the electron charge in other nearby polar or nonpolar molecules, thereby inducing further polarization. The tendency of such permanent dipoles to align with each other results in a net attractive force. Because of fixed distortion in the distribution of electric charge in the very structure of some molecules, one side of a molecule is always somewhat positive and the opposite side somewhat negative. First, the molecules of some materials, although electrically neutral, may be permanent electric dipoles.
Van der Waals forces may arise from three sources. Solids that are held together by van der Waals forces characteristically have lower melting points and are softer than those held together by the stronger ionic, covalent, and metallic bonds. The forces are named for the Dutch physicist Johannes Diderik van der Waals, who in 1873 first postulated these intermolecular forces in developing a theory to account for the properties of real gases. Van der Waals forces, relatively weak electric forces that attract neutral molecules to one another in gases, in liquefied and solidified gases, and in almost all organic liquids and solids. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.
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