- van der Waals forces
Relatively weak electrical forces that attract neutral (uncharged) molecules to each other in gases, liquefied and solidified gases, and almost all organic liquids and solids.Solids held together by van der Waals forces typically have lower melting points and are softer than those held together by ionic, covalent, or metallic bonds (see bonding). The forces arise because neutral molecules, though uncharged, are usually electric dipoles, which have a tendency to align with each other and to induce further polarization in neighbouring molecules, resulting in a net attractive force. They are somewhat weaker than the forces involved in hydrogen bonding. See also Johannes D. van der Waals.
* * *▪ chemistry and physicsrelatively 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. The forces are named for the Dutch physicist Johannes van der Waals (Waals, Johannes Diederik van der), who in 1873 first postulated these intermolecular forces in developing a theory to account for the properties of real gases. 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.Van der Waals forces may arise from three sources. First, the molecules of some materials, although electrically neutral, may be permanent electric dipoles (electric dipole). 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. The tendency of such permanent dipoles to align with each other results in a net attractive force. 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 (see Figure—>). An additional attractive force results from the interaction of a permanent dipole with a neighbouring induced dipole. 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.The nature of the attractive force in molecules, which requires quantum mechanics for its correct description, was first recognized (1930) by the Polish-born physicist Fritz London (London, Fritz Wolfgang), who traced it to electron motion within molecules. London pointed out that at any instant the centre of negative charge of the electrons and the centre of positive charge of the atomic nuclei would not be likely to coincide. Thus, the fluctuation of electrons makes molecules time-varying dipoles, even though the average of this instantaneous polarization over a brief time interval may be zero. Such time-varying dipoles, or instantaneous dipoles, cannot orient themselves into alignment to account for the actual force of attraction, but they do induce properly aligned polarization in adjacent molecules, resulting in attractive forces. These specific interactions, or forces, arising from electron fluctuations in molecules (known as London forces, or dispersion forces) are present even between permanently polar molecules and produce, generally, the largest of the three contributions to intermolecular forces.
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См. также в других словарях:
van der Waals forces — van dər .wȯlz n pl the relatively weak attractive forces that are operative between neutral atoms and molecules and that arise because of the electric polarization induced in each of the particles by the presence of other particles Waals wäls… … Medical dictionary
van der Waals forces — van der Valso jėgos statusas T sritis Standartizacija ir metrologija apibrėžtis Elektrinės kilmės molekulių sąveikos jėgos. atitikmenys: angl. van der Waals forces vok. Van der Waalssche Kräfte, f rus. ван дер ваальсовые силы, f; силы Ван дер… … Penkiakalbis aiškinamasis metrologijos terminų žodynas
van der Waals' forces — [van′dər wôlz΄, vän′dər välz΄] n. [after VAN DER WAALS Johannes Diderik] weak attractive forces between electrically neutral atoms and molecules … English World dictionary
van der Waals forces — van der Valso jėgos statusas T sritis chemija apibrėžtis Elektrinės kilmės molekulių sąveikos jėgos. atitikmenys: angl. van der Waals forces rus. Ван дер Ваальсовые силы; силы Ван дер Ваальса … Chemijos terminų aiškinamasis žodynas
Van der Waals Forces — Van der Waals Forces Ван дер ваальсовы силы (силы Ван дер Вальса) Силы взаимодействия между молекулами или частицами. Межмолекулярные ван дер ваальсовы силы определяются тремя составляющими – лондоновскими силами (см. London forces),… … Толковый англо-русский словарь по нанотехнологии. - М.
van der Waals' forces — Physical Chem. weak, nonspecific forces between molecules. Also, van der Waals forces. [1925 30; see VAN DER WAALS EQUATION] * * * van der Waals forces /van der wälz (or välz) fōrˈsis/ (chem) plural noun Weak attractive forces between molecules,… … Useful english dictionary
van der Waals' forces — Physical Chem. weak, nonspecific forces between molecules. Also, van der Waals forces. [1925 30; see VAN DER WAALS EQUATION] * * * … Universalium
van der Waals' forces — van′ der Waals forc es [[t]ˈvæn dər ˌwɑlz, ˌwɑls[/t]] n. pl. chem. weakly attractive forces that act between neutral atoms or molecules • Etymology: 1925–30; after J. D. van der Waals (1837–1923), Dutch physicist … From formal English to slang
van der Waals forces — [ˌvan də wα:lz, vα:lz] plural noun Chemistry weak, short range electrostatic attractive forces between uncharged molecules, arising from the interaction of permanent or transient electric dipole moments. Origin C19: named after the Dutch… … English new terms dictionary
van der Waals forces — noun plural Etymology: Johannes D. van der Waals died 1923 Dutch physicist Date: 1939 the relatively weak attractive forces that act on neutral atoms and molecules and that arise because of the electric polarization induced in each of the… … New Collegiate Dictionary