# JEE Main & Advanced Chemistry Chemical Bonding and Molecular Structure Valence Shell Electron Pair Repulsion Theory (VSEPR )

Valence Shell Electron Pair Repulsion Theory (VSEPR )

Category : JEE Main & Advanced

The basic concept of the theory was suggested by Sidgwick and Powell (1940). It provides useful idea for predicting shapes and geometries of molecules. The concept tells that, the arrangement of bonds around the central atom depends upon the repulsions operating between electron pairs(bonded or non bonded) around the central atom. Gillespie and Nyholm developed this concept as VSEPR theory.

The main postulates of VSEPR theory are

(1) For polyatomic molecules containing 3 or more atoms, one of the atoms is called the central atom to which other atoms are linked.

(2) The geometry of a molecule depends upon the total number of valence shell electron pairs (bonded or not bonded) present around the central atom and their repulsion due to relative sizes and shapes.

(3) If the central atom is surrounded by bond pairs only. It gives the symmetrical shape to the molecule.

(4) If the central atom is surrounded by lone pairs (lp) as well as bond pairs (bp) of  then the molecule has a distorted geometry.

(5) The relative order of repulsion between electron pairs is as follows : lp - lp > lp - bp > bp - bp.

A lone pair is concentrated around the central atom while a bond pair is pulled out between two bonded atoms. As such repulsion becomes greater when a lone pair is involved.

Geometry of Molecules/Ions having bond pair as well as lone pair of electrons

 Type of mole-cule No. of bond pairs of electron No. of lone pairs of electrons Hybridi-zation Bond angle Expected geometry Actual geometry Examples $A{{X}_{3}}$ 2 1 $s{{p}^{2}}$ < 120o Trigonal planar V-shape, Bent, Angular SO2, SnCl2, NO2– $A{{X}_{4}}$ 2 2 $s{{p}^{3}}$ < 109o 28' Tetrahedral V-shape, Angular H2O, H2S, SCl2, OF2, NH2–, ClO2– $A{{X}_{4}}$ 3 1 $s{{p}^{3}}$ < 109o 28' Tetrahedral Pyramidal NH3, NF3 , PCl3, PH3, AsH3, ClO3– , H3O+ $A{{X}_{5}}$ 4 1 $s{{p}^{3}}d$ < 109o 28' Trigonal bipyramidal Irregular tetrahedron SF4, SCl4, TeCl4 $A{{X}_{5}}$ 3 2 $s{{p}^{3}}d$ 90o Trigonal bipyramidal T-shaped ICl3, IF3, ClF3 $A{{X}_{5}}$ 2 3 $s{{p}^{3}}d$ 180o Trigonal bipyramidal Linear XeF2, I3­–, ICl2– $A{{X}_{6}}$ 5 1 $s{{p}^{3}}{{d}^{2}}$ < 90o Octahedral Square pyramidal ICl5, BrF5, IF5 $A{{X}_{6}}$ 4 2 $s{{p}^{3}}{{d}^{2}}$ – Octahedral Square planar XeF4, ICl4– AX7 6 1 $s{{p}^{3}}{{d}^{3}}$ – Pentagonal pyramidal Distorted octahedral XeF6

##### Notes - Valence Shell Electron Pair Repulsion Theory (VSEPR )

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