 valence shell electron pair repulsion (vsepr) theory is a model used, in chemistry, to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms.jolly, w. l.,modern inorganic chemistry, mcgraw-hill, 1984, p.77-90. isbn 0-07-032760-2 it is also named gillespieânyholm theory after its two main developers. the acronym "vsepr" is occasionally pronounced "vesper" or "vuh-seh-per". the premise of vsepr is that the valence electron pairs surrounding an atom tend to repel each other, and will therefore adopt an arrangement that minimizes this repulsion, thus determining the molecule's geometry. the sum of the number of atoms bonded to a central atom and the number of lone pairs formed by its nonbonding valence electrons is known as the central atom's steric number. vsepr theory is usually compared with valence bond theory, which addresses molecular shape through orbitals that are energetically accessible for bonding. valence bond theory concerns itself with the formation of sigma and pi bonds. molecular orbital theory is another model for understanding how atoms and electrons are assembled into molecules and polyatomic ions. vsepr theory has long been criticized for not being quantitative, and therefore limited to the generation of "crude" (though structurally accurate) molecular geometries of covalently-bonded molecules. however, molecular mechanics force fields based on vsepr have also been developed. ==history== the idea of a correlation between molecular geometry and number of valence electrons (both shared and unshared) was originally proposed in 1939 by ryutaro tsuchida in japan, and was independently presented in a bakerian lecture in 1940 by nevil sidgwick and herbert powell of the university of oxford.http://rspa.royalsocietypublishing.org/content/176/965/153.abstract n.v.sidgwick and h.m.powell, proc.roy.soc.a 176, 153â180 (1940) bakerian lecture. stereochemical types and valency groups in 1957, ronald gillespie and ronald sydney nyholm of university college london refined this concept into a more detailed theory, capable of choosing between various alternative geometries.r.j.gillespie and r.s.nyholm, quart.rev. 11, 339 (1957)r.j.gillespie, j.chem.educ. 47, 18(1970) == description == vsepr theory, occasionally pronounced "vesper" or &q
Chemistry_theories Molecular_geometry Quantum_chemistry Stereochemistry