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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