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The Valence Shell Electron Pair Repul-Sion (Vspert), Theory, The main postulates of VSEPR theory are as follows:, , The shape of a molecule depends upon the, number of valence shell electron pairs (bonded, or nonbonded) around the central atom., , Pairs of electrons in the valence shell repel one, another since their electron clouds are, negatively charged, , These pairs of electrons tend to occupy such, positions in space that minimise repulsion and, thus maximise distance between them., , The valence shell is taken as a sphere with the, electron pairs localising on the spherical, surface at maximum distance from one, another., , 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., , Where two or more resonance structures can, represent a molecule, the VSEPR model is, applicable to any such structure., , The repulsive interaction of electron pairs de-crease, , in the order:, Lone pair (Ip) - Lone pair (Ip) > Lone pair (Ip) - Bond, pair (bp) > Bond pair (bp) - Bond pair (bp)