Electron pairs repel each other

Oct 13, 2025 by leolavanderia.com.br 116 views

Introduction

In the realm of chemistry, understanding the structure and properties of molecules is essential for grasping various chemical phenomena. One of the fundamental theories that help us predict the molecular geometry and bond angles of molecules is the Valence Shell Electron Pair Repulsion (VSEPR) theory. In this article, we will delve into the concept of VSEPR, its significance, and how it can be applied to predict the molecular geometry and bond angles of molecules.

What is VSEPR?

VSEPR is a theory that explains the shape of molecules based on the repulsion between electron pairs in the valence shell of an atom. The theory was first proposed by Sidgwick and Powell in 1940 and later developed by Nyholm and Gillespie in the 1950s. According to VSEPR, the shape of a molecule is determined by the number of electron pairs (bonding and non-bonding) around the central atom.

Key Principles of VSEPR

The VSEPR theory is based on the following key principles:

Electron pairs repel each other: Electron pairs in the valence shell of an atom repel each other due to electrostatic forces.
Molecular shape is determined by electron pair geometry: The shape of a molecule is determined by the arrangement of electron pairs around the central atom.
Bond angles are determined by electron pair repulsion: The bond angles between atoms in a molecule are determined by the repulsion between electron pairs.

Predicting Molecular Geometry and Bond Angles using VSEPR

To predict the molecular geometry and bond angles of molecules using VSEPR, we need to follow these steps:

Determine the central atom: Identify the central atom in the molecule.
Count the number of electron pairs: Count the number of electron pairs (bonding and non-bonding) around the central atom.
Determine the electron pair geometry: Determine the electron pair geometry based on the number of electron pairs.
Determine the molecular shape: Determine the molecular shape based on the electron pair geometry.
Determine the bond angles: Determine the bond angles based on the repulsion between electron pairs.

Examples of Molecular Geometry and Bond Angles

Let's consider some examples to illustrate how VSEPR can be used to predict the molecular geometry and bond angles of molecules.

Example 1: Water (H2O)

Central atom: Oxygen (O)
Number of electron pairs: 4 (2 bonding pairs and 2 non-bonding pairs)
Electron pair geometry: Tetrahedral
Molecular shape: Bent or V-shape
Bond angles: 104.5°

Example 2: Ammonia (NH3)

Central atom: Nitrogen (N)
Number of electron pairs: 4 (3 bonding pairs and 1 non-bonding pair)
Electron pair geometry: Tetrahedral
Molecular shape: Trigonal pyramidal
Bond angles: 107.3°

Example 3: Carbon Dioxide (CO2)

Central atom: Carbon (C)
Number of electron pairs: 4 (2 bonding pairs and 2 non-bonding pairs)
Electron pair geometry: Linear
Molecular shape: Linear
Bond angles: 180°

Conclusion

In conclusion, the VSEPR theory is a powerful tool for predicting the molecular geometry and bond angles of molecules. By understanding the principles of VSEPR, we can determine the electron pair geometry, molecular shape, and bond angles of molecules. The examples provided in this article illustrate how VSEPR can be applied to predict the molecular geometry and bond angles of molecules.

References

Sidgwick, N. V., & Powell, H. M. (1940). The Electronic Theory of Valency. Oxford University Press.
Nyholm, R. S., & Gillespie, R. J. (1957). The Electronic Theory of Valency. Journal of the Chemical Society, 1957, 443-453.