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24-581: (Redirected from LF ) [REDACTED] Look up LF in Wiktionary, the free dictionary. Lf or LF may refer to: Arts and entertainment [ edit ] LF (album) , by Raymond Lam Left fielder , a position in baseball Laxius Force , a role-playing video game trilogy Libby Folfax, a character in Jimmy Neutron: Boy Genius Lifeforce (film) ,

48-523: A 1985 film directed by Tobe Hooper Salamander (video game) , an arcade game retitled Life Force Companies and organisations [ edit ] LeapFrog Enterprises , an educational toy company Lebanese Forces , a Lebanese political party Li & Fung , a company of Hong Kong Linux Foundation , a non-profit organization for the promotion of Linux LoveFilm , UK-based provider of home video and video game rental through DVD-by-mail and streaming video on demand People's Life First ,

72-651: A Japanese political party FlyNordic (IATA airline designator LF), a defunct Swedish airline Nippon Broadcasting System , also known as JOLF, a radio station in Tokyo, Japan Places [ edit ] Lakeland, Florida Livermore Falls, Maine Lambeau Field , a stadium in Green Bay, Wisconsin and the home of the Green Bay Packers Science and technology [ edit ] Biology and medicine [ edit ] Lactoferrin ,

96-601: A concept automobile LF-routes , a network of long-distance cycling routes in the Netherlands and Belgium . Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Lf . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Lf&oldid=1192294752 " Category : Disambiguation pages Hidden categories: Short description

120-444: A large polarizability implies that the electrons are more easily redistributed. This trend is exemplified by the halogens (from smallest to largest: F 2 , Cl 2 , Br 2 , I 2 ). The same increase of dispersive attraction occurs within and between organic molecules in the order RF, RCl, RBr, RI (from smallest to largest) or with other more polarizable heteroatoms . Fluorine and chlorine are gases at room temperature, bromine

144-472: A level of syntactic representation Logical framework , in automated theorem proving LF (logical framework) , a particular logical framework Other uses in science and technology [ edit ] Missile launch facility , a structure used for launching ballistic missiles Limestone filler, used in cement and concrete fabrication Line feed character, in typing and computing; also called newline, line break, or end-of-line Lineal foot ,

168-416: A measurement of length without regard to width Load factor (disambiguation) Logic File , a logic file category London forces , a type of intermolecular forces Low frequency , a radio frequency between 30 and 300 kHz Other uses [ edit ] Laissez-faire , a concept in economics Left fielder , a defensive position in baseball Left Front (disambiguation) Lexus LF ,

192-557: A protein Lateral flow test , an immunologic test Lymphatic filariasis , a disease common in tropical regions L.f. , taxonomic author abbreviation of Carl Linnaeus the Younger (1741–1783), Swedish naturalist Logic and information theory [ edit ] Lexical function , a tool for the description of semantic relationships Logical form , the abstract form of a set of sentences in logic Logical form (linguistics) ,

216-521: Is a liquid, and iodine is a solid. The London forces are thought to arise from the motion of electrons. The first explanation of the attraction between noble gas atoms was given by Fritz London in 1930. He used a quantum-mechanical theory based on second-order perturbation theory . The perturbation is because of the Coulomb interaction between the electrons and nuclei of the two moieties (atoms or molecules). The second-order perturbation expression of

240-610: Is described in terms of a "non-retarded" Hamaker constant. For entities that are farther apart, the finite time required for the fluctuation at one atom to be felt at a second atom ("retardation") requires use of a "retarded" Hamaker constant. While the London dispersion force between individual atoms and molecules is quite weak and decreases quickly with separation R {\displaystyle R} like 1 R 6 {\displaystyle {\frac {1}{R^{6}}}} , in condensed matter (liquids and solids),

264-730: Is different from Wikidata All article disambiguation pages All disambiguation pages LF">LF Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.133 via cp1102 cp1102, Varnish XID 541412412 Upstream caches: cp1102 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 05:38:57 GMT London forces The electron distribution around an atom or molecule undergoes fluctuations in time. These fluctuations create instantaneous electric fields which are felt by other nearby atoms and molecules, which in turn adjust

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288-431: Is the distance between the nuclear centers of mass of the moieties. This expansion is known as the multipole expansion because the terms in this series can be regarded as energies of two interacting multipoles, one on each monomer. Substitution of the multipole-expanded form of V into the second-order energy yields an expression that resembles an expression describing the interaction between instantaneous multipoles (see

312-411: Is the separation between them. The effects of London dispersion forces are most obvious in systems that are very non-polar (e.g., that lack ionic bonds ), such as hydrocarbons and highly symmetric molecules like bromine (Br 2, a liquid at room temperature) or iodine (I 2, a solid at room temperature). In hydrocarbons and waxes , the dispersion forces are sufficient to cause condensation from

336-419: The dispersion force as the interaction between two such dipoles was invented after London arrived at the proper quantum mechanical theory. The authoritative work contains a criticism of the instantaneous dipole model and a modern and thorough exposition of the theory of intermolecular forces. The London theory has much similarity to the quantum mechanical theory of light dispersion , which is why London coined

360-434: The effect is cumulative over the volume of materials, or within and between organic molecules, such that London dispersion forces can be quite strong in bulk solid and liquids and decay much more slowly with distance. For example, the total force per unit area between two bulk solids decreases by 1 R 3 {\displaystyle {\frac {1}{R^{3}}}} where R {\displaystyle R}

384-489: The following approximation is obtained for the dispersion interaction E A B d i s p {\displaystyle E_{AB}^{\rm {disp}}} between two atoms A {\displaystyle A} and B {\displaystyle B} . Here α A ′ {\displaystyle \alpha '_{A}} and α B ′ {\displaystyle \alpha '_{B}} are

408-474: The formation of instantaneous dipoles that (when separated by vacuum ) attract each other. The magnitude of the London dispersion force is frequently described in terms of a single parameter called the Hamaker constant , typically symbolized A {\displaystyle A} . For atoms that are located closer together than the wavelength of light , the interaction is essentially instantaneous and

432-542: The gas phase into the liquid or solid phase. Sublimation heats of e.g. hydrocarbon crystals reflect the dispersion interaction. Liquification of oxygen and nitrogen gases into liquid phases is also dominated by attractive London dispersion forces. When atoms/molecules are separated by a third medium (rather than vacuum), the situation becomes more complex. In aqueous solutions , the effects of dispersion forces between atoms or molecules are frequently less pronounced due to competition with polarizable solvent molecules. That is,

456-407: The instantaneous fluctuations in one atom or molecule are felt both by the solvent (water) and by other molecules. Larger and heavier atoms and molecules exhibit stronger dispersion forces than smaller and lighter ones. This is due to the increased polarizability of molecules with larger, more dispersed electron clouds . The polarizability is a measure of how easily electrons can be redistributed;

480-538: The interaction energy contains a sum over states. The states appearing in this sum are simple products of the stimulated electronic states of the monomers . Thus, no intermolecular antisymmetrization of the electronic states is included, and the Pauli exclusion principle is only partially satisfied. London wrote a Taylor series expansion of the perturbation in 1 R {\displaystyle {\frac {1}{R}}} , where R {\displaystyle R}

504-452: The phrase "dispersion effect". In physics, the term "dispersion" describes the variation of a quantity with frequency, which is the fluctuation of the electrons in the case of the London dispersion. Dispersion forces are usually dominant over the three van der Waals forces (orientation, induction, dispersion) between atoms and molecules, with the exception of molecules that are small and highly polar, such as water. The following contribution of

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528-452: The polarizability volumes of the respective atoms. The quantities I A {\displaystyle I_{A}} and I B {\displaystyle I_{B}} are the first ionization energies of the atoms, and R {\displaystyle R} is the intermolecular distance. Note that this final London equation does not contain instantaneous dipoles (see molecular dipoles ). The "explanation" of

552-421: The qualitative description above). Additionally, an approximation, named after Albrecht Unsöld , must be introduced in order to obtain a description of London dispersion in terms of polarizability volumes , α ′ {\displaystyle \alpha '} , and ionization energies , I {\displaystyle I} , (ancient term: ionization potentials ). In this manner,

576-404: The spatial distribution of their own electrons. The net effect is that the fluctuations in electron positions in one atom induce a corresponding redistribution of electrons in other atoms, such that the electron motions become correlated. While the detailed theory requires a quantum-mechanical explanation (see quantum mechanical theory of dispersion forces ) , the effect is frequently described as

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