In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer to intermolecular forces that deal with forces due to the polarization of molecules. Forces that deal with fixed or angle averaged dipoles (Keesom forces) and free or rotation dipoles (Debye forces) as well as shifts in electron cloud distribution (London Forces) are named after the Dutch chemist Johannes Diderik van der Waals who first documented these interactions. The Lennard-Jones potential is often used as an approximate model for the Van der Waals force as a function of distance. Chemistry (derived from the Arabic word kimia, alchemy, where al is Arabic for the) is the science that deals with the properties of organic and inorganic substances and their interactions with other organic and inorganic substances. ... Intermolecular forces are electromagnetic forces which act between molecules or between widely separated regions of a macromolecule. ... The Keesom force is an intermolecular force resulting from the angle-averaged dipole-dipole interaction between two atoms or molecules and its potential. ... This article is about the electromagnetic phenomenon. ... van der Waals Johannes Diderik Van der Waals (November 23, 1837 – March 8, 1923) was a Dutch scientist famous for his work on the equation of state for gases and liquids, for which he won the Nobel Prize in physics in 1910. ... Neutral atoms and molecules are subject to two distinct forces in the limit of large distance, and short distance. ...

Van der Waals interactions are observed in noble gases, which are very stable and tend not to interact. This is why it is difficult to condense them into liquids. However, the larger the atom of the noble gas (the more electrons it has), the easier it is to condense the gas into a liquid. This happens because when the electron cloud surrounding the gas atom gets large, it does not form a perfect sphere around the nucleus. Rather, it's only spherical if averaged over longer times and generally forms an oval, which has a slight negative charge on one side and a slight positive charge on the other. The atom becomes a temporary dipole. This induces the same shift in neighboring atoms and spreads from one atom to the next. Unlike charges attract and the induced dipoles are held together by dispersion force (or Van der Waals force). Van der Waals forces are responsible for certain cases of pressure broadening (Van der Waals broadening) of spectral lines. The noble gases are the chemical elements in group 18 (old-style Group 0) of the periodic table. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... A liquid will assume the shape of its container. ... Properties An atom (Greek άτομον from ά: non and τομον: divisible) is a submicroscopic structure found in all ordinary matter. ... Electron cloud is a term used for introducing the concept of wavefunction in low-level pedagogical introductions to atomic physics, molecular physics, chemistry or quantum chemistry. ... A stylized representation of a lithium atom. ... In mathematics, an ellipse (from the Greek for absence) is a plane algebraic curve where the sum of the distances from any point on the curve to two fixed points is constant. ... A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ...

The Van der Waals force is the force to which the gecko's climbing ability is attributed. A gecko can hang on a glass surface using only one toe. Efforts continue to create a synthetic "gecko tape" that exploits this knowledge. So far research has produced some promising results - early research yielded an adhesive tape [1] product, which only obtains a fraction of the forces measured from the natural material, and new research [2] has yielded a discovery that purports 200 times the adhesive forces of the natural material. Geckos are small to moderately large lizards belonging to the family Gekkonidae and found in warm climates throughout the world. ... Two rolls of adhesive tape. ...

London dispersion force

Interaction energy of argon dimer. Long-range part is due to London forces

London dispersion forces, named after the German-American physicist Fritz London, are weak intermolecular forces that arise from the attractive force between transient dipoles (or better multipoles) in molecules without permanent multipole moments. London forces are also just called dispersion forces or London forces and sometimes van der Waals forces. Image File history File links Download high resolution version (1500x1050, 33 KB) Summary Description: Interaction energy of argon dimer. ... Image File history File links Download high resolution version (1500x1050, 33 KB) Summary Description: Interaction energy of argon dimer. ... Fritz Wolfgang London (March 7, 1900–March 30, 1954) was a Jewish German-American physicist for whom the London force is named. ... Intermolecular forces are electromagnetic forces which act between molecules or between widely separated regions of a macromolecule. ... The Earths magnetic field, which is approximately a dipole. ... A molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Multipole moments in mathematics and mathematical physics are an orthogonal basis for the decomposition of a function, based on the response of a field to point sources that are brought infinitely close to each other. ...

London forces can be exhibited by nonpolar molecules because electron density moves about a molecule probabilistically. There is a high chance that the electron density will not be evenly distributed throughout a nonpolar molecule. When an uneven distribution occurs, a temporary multipole is created. This multipole may interact with other nearby multipoles. London forces are also present in polar molecules, but they are usually only a small part of the total interaction force.

Electron density in a molecule may be redistributed by proximity to another multipole. Electrons will gather on the side of a molecule that faces a positive charge and retreat from a negative charge. Hence, a transient multipole can be produced by a nearby polar molecule, or even a transient multipole in another nonpolar molecule. Electron density is the measure of the probability of an electron being present at a specific location. ...

London forces are weaker than other intermolecular forces such as ionic interactions, hydrogen bonding, or permanent dipole-dipole interactions. Intermolecular forces are electromagnetic forces which act between molecules or between widely separated regions of a macromolecule. ... Hydrogen bonds between water molecules are diagramatically represented by the black lines. ...

This phenomenon is the only attractive intermolecular force at large distances present between neutral atoms (e.g. helium), and is the major attractive force between non-polar molecules, such as nitrogen, or methane (to name a few). Without London forces, there would be no attractive force between rare gas atoms and they could not then be obtained in a liquid form. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... R-phrases S-phrases , , , Flash point −188 °C Autoignition temperature 537 °C Explosive limits 5–15% Supplementary data page Structure and properties Thermodynamic data Spectral data UV, IR, NMR, MS Related compounds Related alkanes Ethane Propane Related compounds Methanol Chloromethane Except where noted otherwise, data are given for materials in... The noble gases are the chemical elements in group 18 (old-style Group 0) of the periodic table. ...

London forces become stronger as the atom (or molecule) in question becomes larger. This is due to the increased polarizability of molecules with larger, more dispersed electron clouds. This trend is exemplified by the halogens (from smallest to largest: F₂, Cl₂, Br₂, I₂). Fluorine and chlorine are gases at room temperature, bromine is a liquid, and iodine is a solid. The halogens are a chemical series. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... General Name, Symbol, Number bromine, Br, 35 Chemical series halogens Group, Period, Block 17, 4, p Appearance gas/liquid: red-brown solid: metallic luster Atomic mass 79. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ...

Relation to the Casimir effect

The London-Van der Waals force is related to the Casimir effect for dielectric media, the former the microscopic description of the latter bulk property. First detailed calculations of this were done 1955 by E. M. Lifshitz. This equivalence gained attention and some new papers, in the recent discussion of sonoluminescence. In 1948 Dutch physicist Hendrik B. G. Casimir of Philips Research Labs predicted that two uncharged parallel metal plates will be subject to a force pressing them together. ... 1955 (MCMLV) was a common year starting on Saturday of the Gregorian calendar. ... Evgeny Mikhailovich Lifshitz (Евгений Михайлович Лифшиц) (February 21, 1915 – October 29, 1985) was a Russian physicist. ... Image of multi-bubble sonoluminescence created by a high intensity ultrasonic horn immersed in a beaker of liquid. ...

See also

• Chemical bond
• Hydride
• John Lennard-Jones
• Lennard-Jones potential

A chemical bond is the physical phenomenon of chemical substances being held together by attraction of atoms to each other through electrons or by electrostatic forces. ... A hydride is a compound of hydrogen with less electronegative elements. ... John Edward Lennard-Jones (October 27, 1894 - November 1, 1954) was a mathematician who held a chair of theoretical physics at Bristol University, and then a chair of theoretical science at Cambridge University. ... Neutral atoms and molecules are subject to two distinct forces in the limit of large distance, and short distance. ...

References

• E. M. Lifshitz, Zh. Eksp. Teor. Fiz. 29, 894 (1955)
  • English translation: Soviet Phys. JETP 2, 73 (1956)
• I. D. Dzyaloshinskii, E. M. Lifshitz, and L. P. Pitaevskii, Usp. Fiz. Nauk 73, 381 (1961)
  • English translation: Soviet Phys. Usp. 4, 153 (1961)
• L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media, Pergamon, Oxford, 1960, pp. 368–376.

External links

• R. H. French, University of Pennsylvania, Materials Science "Full Spectral London Dispersion Interaction: Forces and Energies".
• Western Oregon University's "London force". Intermolecular Forces. (animation)
• Lefers, Mark, "Van der Waals dispersion force". Holmgren Lab.
• Iver Brevik, V. N. Marachevsky, Kimball A. Milton, Identity of the Van der Waals Force and the Casimir Effect and the Irrelevance of these Phenomena to Sonoluminescence, hep-th/9901011