Sidgwick and Powell (1940) proposed VSEPR theory on the basis of repulsive interaction of the electron pairs in the valence shell of the atoms, this theory was further developed by Nyholm and Gillespie (1950).
Main Postulates of VSEPR Theory-
(i) The shape of a molecule depends upon the number of valence shell electron pairs (bonded or non-bonded) around the central atom.
(ii) Electron pairs in the valence shell repel one another since their electron clouds are negatively charged.
(iii) These electron pairs tend to occupy such positions in space that minimize repulsion and so maximize distance between them.
(iv) The valence shell is taken as a sphere with the electron pairs localizing on the spherical surface at maximum distance from one another.
(v) A multiple bond is treated as if it is a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair.
(vi) When two or more resonating structures can represent a molecule, the VSEPR model is applicable to any such structure.
