Chemistry Concepts: The Application of VSEPR Theory

by Yuvi K - December 16, 2023

Introduction to VSEPR Theory

VSEPR stands for Valence Shell Electron Pair Repulsion. VSEPR Theory is a model that is used to predict the shapes of molecules based on the arrangement of electron pairs around the central atom of the molecule. This theory states that when two or more electron pairs are present around the central atom, the electron pairs will arrange themselves in such a way that they are maximally distant from each other. This theory was proposed in the year 1957 by the scientist G.N. Lewis and was further developed by the scientist J. A. Pople.

Application of VSEPR Theory in Chemistry

VSEPR Theory is an important concept in Chemistry and plays a vital role in predicting the shapes of molecules. It is used to predict the geometrical structure of a molecule, that is, the 3-dimensional arrangement of the atoms in the molecule. It also helps in understanding the bond angles between the bonded atoms of the molecule.

Let’s take the example of a molecule of water with a total of 24 valence electrons. According to the VSEPR Theory, the two bonding pairs and two lone pairs of electrons are arranged around the oxygen atom in such a way that the total repulsion between them is minimized. The oxygen atom is present in the centre and the two hydrogen atoms are on the opposite ends and hence, form a bent structure. The bond angle between the hydrogen atoms and the oxygen atom is approximately 104.5°.

Rules of VSEPR Theory

VSEPR Theory is based on two important rules which are explained below:

1. Number of Electron Regions

The first rule states that the number of regions of electron density around the central atom of the molecule is equal to the number of atoms bonded to it plus the number of lone pairs of electrons. For example, for a molecule of water, the total number of electron regions is four, two for the hydrogen atoms, one for each of the lone pairs, and one for the oxygen atom.

2. Electron Pair Geometry

The second rule of the VSEPR Theory is that the arrangement of the electron pairs around the central atom of the molecule is such that the electron pairs are maximally distant from each other. This implies that the electron pairs are arranged in a geometrical structure such that the repulsion between them is minimized. Therefore, the electron pair geometry of the molecules determines their shape.

Table of Common Molecule Shapes and Bond Angles

The table given below provides a summary of the common shapes of molecules and their bond angles according to the VSEPR Theory.

Conclusion

VSEPR Theory is an important concept in Chemistry and helps us understand the shapes of molecules and their bond angles. It is based on two important rules, namely the number of electron regions and the electron pair geometry. This theory is applicable to all molecules and helps us in predicting their shapes and bond angles.