Valence Shell Electron Pair Repulsion (VSEPR) Theory :- Full Study

Introduction (VSEPR) Theory :-

VSEPR theory is the simplest theory for predicting the geometries of molecules . Valence Shell Electron Repulsion theory was first proposed by Sidwick and Powell in the year 1940 but it was given the final shape by Gillespie and Nyholm in the year 1957 . 

Principle : VSEPR Theory is based on the repulsive interactions between the electron pairs in the valence shell of the atom .

According to this theory , the shapes of molecules can be determined by the number of electron pairs in the valence shell of the central atoms. These electron pairs experience electrostatic repulsions from one another and the bonded atoms in a molecule adopt that particular arrangement in space around the central atom which keeps on the average as far apart as possible.

Main points of Valence Shell Electron Pair Repulsion (VSEPR) Theory :-

1. Geometry of a molecule depends upon the total number of valence shell electron pairs (both bonded or non bonded) around the central atom in the molecule .
2. Repulsion between valence shell electron pairs determines the molecular shape.
3. To minimise the repulsion between electrons or to aquire a state of minimum energy or maximum stability , the valence shell electron pairs should keep as far apart as possible.
4. The most stable arrangement in case of more than one geometrical arrangement is possible is as follows :
5. a. Lone pair - Lone pair repulsion is greater than Lone pair - Bond pair repulsion which is greater than Bond pair - Bond pair repulsion .
6. b. Repulsion between electron pairs at vertices greater than 115° apart can be neglected .

Limitations of VSEPR Theory :-

1. This theory is applicable for only covalent compounds and not for ionic compounds .
2. The theory didn't make any distinctions between s, p, d and f orbitals.
3. This theory does not help in prediction of shapes of coordination compounds . etc.

This is all about VSEPR theory , hope this will be useful to you .

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