Editing VSEPR theory (section)

{{Short description|Model for predicting molecular geometry}}
[[File:Water-dimensions-from-Greenwood&Earnshaw-2D.png|thumb|Example of bent electron arrangement (water molecule). Shows location of unpaired electrons, bonded atoms, and bond angles.  The bond angle for water is 104.5°.]]

'''Valence shell electron pair repulsion''' ('''VSEPR''') '''theory''' ({{IPAc-en|ˈ|v|ɛ|s|p|ər|,_|v|ə|ˈ|s|ɛ|p|ər}} {{respell|VESP|ər}},<ref name="Petrucci" />{{rp|410}} {{respell|və|SEP|ər}}<ref name="H2009">{{cite book|first= H. Stephen |last=Stoker|title = General, Organic, and Biological Chemistry|publisher = Cengage Learning|year = 2009|isbn = 978-0-547-15281-3|page=119}}</ref>) is a [[conceptual model|model]] used in [[chemistry]] to predict the geometry of individual [[molecule]]s from the number of [[electron pair]]s surrounding their central atoms.<ref name="Jolly">{{cite book |last=Jolly |first=W. L. |title=Modern Inorganic Chemistry |publisher=McGraw-Hill |year=1984 |pages=[https://archive.org/details/trent_0116300649799/page/77 77–90] |isbn=978-0-07-032760-3 |url=https://archive.org/details/trent_0116300649799/page/77 }}</ref> It is also named the Gillespie-Nyholm theory after its two main developers, [[Ronald Gillespie]] and [[Ronald Sydney Nyholm|Ronald Nyholm]].

The premise of VSEPR is that the [[valence electron]] pairs surrounding an atom tend to repel each other. The greater the repulsion, the higher in energy (less stable) the molecule is. Therefore, the VSEPR-predicted [[molecular geometry]] of a molecule is the one that has as little of this repulsion as possible.  Gillespie has emphasized that the electron-electron repulsion due to the [[Pauli exclusion principle]] is more important in determining molecular geometry than the [[electrostatic repulsion]].<ref name="Fiftyyears">{{cite journal | last1 = Gillespie | first1 = R. J. | year = 2008 | title = Fifty years of the VSEPR model | journal = Coord. Chem. Rev. | volume = 252 | issue = 12–14| pages = 1315–1327 | doi=10.1016/j.ccr.2007.07.007}}</ref>

The insights of VSEPR theory are derived from topological analysis of the [[electron density]] of molecules. Such quantum chemical topology (QCT) methods include the [[electron localization function]] (ELF) and the [[atoms in molecules|quantum theory of atoms in molecules]] (AIM or QTAIM).<ref name="Fiftyyears"/><ref>{{cite journal | last1 = Bader | first1 = Richard F. W. | last2 = Gillespie | first2 = Ronald J. | last3 = MacDougall | first3 = Preston J. | year = 1988 | title = A physical basis for the VSEPR model of molecular geometry | journal = J. Am. Chem. Soc. | volume = 110 | issue = 22 | pages = 7329–7336 | doi=10.1021/ja00230a009| bibcode = 1988JAChS.110.7329B }}</ref>