In chemistry, the term van der Waals' forces (sometimes called London dispersion forces) refers to a particular class of intermolecular forces. The term originally referred to all such forces, and this usage is still sometimes observed, but it is now more commonly used to refer to those forces which arise from the polarization of molecules into dipoles. This includes forces that arise from fixed or angle-averaged dipoles (Keesom forces) and free or rotation dipoles (Debye forces) as well as shifts in electron cloud distribution (London forces). The name refers to the Dutch physicist and chemist Johannes Diderik van der Waals, who first documented these types of forces. The Lennard-Jones potential is often used as an approximate model for the Van der Waals force as a function of distance. Chemistry (from Greek χημεία khemeia[1] meaning alchemy) is the science of matter at the atomic to molecular scale, dealing primarily with collections of atoms, such as molecules, crystals, and metals. ... Intermolecular forces are electromagnetic forces which act between molecules or between widely separated regions of a macromolecule. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... // The Earths magnetic field, which is approximately a dipole. ... 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: an attractive van der Waals force, or dispersion force, at long ranges, and a repulsion force, the result of overlapping electron orbitals, referred to as Pauli repulsion (from Pauli exclusion principle). ...

van der Waals' forces 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 is only spherical if averaged over longer times and generally forms an ellipsoid, which has a slight negative charge on one side of the major axis 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. For the musical band, see Noble Gas (band) 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 usually assume the shape of its container. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle of a chemical element that retains its chemical properties. ... 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 semi-accurate depiction of the helium atom. ... 3D rendering of an ellipsoid In mathematics, an ellipsoid is a type of quadric that is a higher dimensional analogue of an ellipse. ... 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. ...

London dispersion force

Interaction energy of argon dimer. The long-range part is due to London dispersion 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 dispersion 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. ... General Name, Symbol, Number argon, Ar, 18 Chemical series noble gases Group, Period, Block 18, 3, p Appearance colorless Atomic mass 39. ... Sucrose, or common table sugar, is composed of glucose and fructose. ... Fritz Wolfgang London (March 7, 1900–March 30, 1954) was a German-born 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. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... 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, see quantum mechanical theory of dispersion forces. 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. Intermolecular forces are electromagnetic forces which act between molecules or between widely separated regions of a macromolecule. ...

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 by 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. ... Snapshot from a simulation of liquid water. ...

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 couple). Without London forces, there would be no attractive force between noble 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. ... Methane is a significant and plentiful fuel which is the principal component of natural gas. ... For the musical band, see Noble Gas (band) 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 exist as diatomic molecules in the gas, liquid and solid phases. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance Yellowish brown 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 major 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' forces 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 in 1955 by E. M. Lifshitz. In physics, the Casimir effect is a physical force exerted between separate objects, which is due to neither charge, gravity, nor the exchange of particles, but instead is due to resonance of all-pervasive energy fields in the intervening space between the objects. ... 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. ...

Use by animals

The van der Waals' forces 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. Subfamilies Aeluroscalabotinae Eublepharinae Gekkoninae Teratoscincinae Diplodactylinae Geckos are small to moderately large lizards belonging to the family Gekkonidae which are found in warm climates throughout the world. ... Two rolls of adhesive tape. ...

Researchers at Stanford University recently developed a gecko-like robot which uses synthetic setae to climb walls [3]. Stanford redirects here. ... ASIMO, a humanoid robot manufactured by Honda. ... Synthetic setae emulate the setae found on the toes of a gecko and scientific research in this area is driven towards the development of dry adhesives. ...

See also

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

A chemical bond is the physical phenomenon (or phenomena) responsible for the attractive interactions between atoms that confers stability to di- and polyatomic chemical compounds. ... A hydride is a compound of hydrogen with more electropositive 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: an attractive van der Waals force, or dispersion force, at long ranges, and a repulsion force, the result of overlapping electron orbitals, referred to as Pauli repulsion (from Pauli exclusion principle). ...

Sources

• 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
• I. D. Dzyaloshinskii, E. M. Lifshitz, and L. P. Pitaevskii, Usp. Fiz. Nauk 73, 381 (1961)
  • English translation: Soviet Phys. Usp. 4, 153 (1961)
• R. H. French, University of Pennsylvania, Materials Science "Full Spectral London Dispersion Interaction: Forces and Energies".
• L. D. Landau and E. M. Lifshitz, Electrodynamics of Continuous Media, Pergamon, Oxford, 1960, pp. 368–376.
• Mark Lefers, "Van der Waals dispersion force". Holmgren Lab.
• E. M. Lifshitz, Zh. Eksp. Teor. Fiz. 29, 894 (1955)
  • English translation: Soviet Phys. JETP 2, 73 (1956)
• Western Oregon University's "London force". Intermolecular Forces. (animation)