VSEPR theory is used to predict the arrangement of electron pairs around central atoms in molecules, especially simple and symmetric molecules. 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. The idea of a correlation between molecular geometry and number of valence electron pairs (both shared and unshared pairs) 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. 5.5 Complexes with strong d-contribution.5.4 Square planar transition metal complexes.Hence, VSEPR is unrelated to wave function based methods such as orbital hybridisation in valence bond theory. Such quantum chemical topology (QCT) methods include the electron localization function (ELF) and the quantum theory of atoms in molecules (AIM or QTAIM). The insights of VSEPR theory are derived from topological analysis of the electron density of molecules.
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. This in turn decreases the molecule's energy and increases its stability, which determines the molecular geometry. 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. It is also named the Gillespie-Nyholm theory after its two main developers, Ronald Gillespie and Ronald Nyholm. Valence shell electron pair repulsion theory, or VSEPR theory ( / ˈ v ɛ s p ər, v ə ˈ s ɛ p ər/ VESP-ər, : 410 və- SEP-ər ), is a model used in chemistry to predict the geometry of individual molecules from the number of electron pairs surrounding their central atoms. (Water molecule) The bond angle for water is 104.5°. Shows location of unpaired electrons, bonded atoms, and bond angles.