Difference between electron geometry and molecular geometry

Last update: 22/05/2023
Author: Sebastian Vidal

Introduction

In chemistry, the study of the structure of molecules is essential to understand its properties physical and chemical. Two important concepts for structure determination are electron geometry and molecular geometry. In this article we are going to explain how these two concepts differ.

Electron Geometry

Electron geometry, also known as electron geometry or Lewis molecular geometry, refers to the arrangement of electrons around the central atom of a molecule. These electrons include the valence electrons, which are those involved in chemical bonds. The geometry of the electron is determined using the valence electron pair repulsion theory (TRPEV) by Gilbert N. Lewis.

TRPEV

This theory states that the electron pairs in the valence shell of an atom tend to be as far apart as possible from each other, due to their repulsive negative charge. According to this theory, the geometry of the electron in a molecule is determined by the number of electron pairs in the valence shell of the central atom. Each type of arrangement of the electronic pairs is assigned a specific name, such as linear, trigonal planar, tetrahedral, among others.

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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. This geometry depends both on the geometry of the electron and on the presence of different atoms or groups of atoms.

different atoms

When there are different atoms in a molecule, the molecular geometry is determined using the electron pair repulsion theory of the central atom. This theory states that electron pairs and dissimilar atoms repel each other, which alters the geometry of the electron. Each type of three-dimensional arrangement is assigned a specific name, such as linear, trigonal planar, tetrahedral, among others.

Examples

An example of a molecule in which the electron geometry and the molecular geometry coincide is the carbon dioxide (CO) molecule.2), whose central atom is carbon, which has a planar trigonal geometry. Other molecules that have different molecular and electron geometries are water (H2O) and ammonia (NH3).

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Conclusions

Although electron geometry and molecular geometry are closely related, there are situations in which they are different. By understanding the differences between these two geometries, one can have a better understanding of the physical and chemical properties of the molecules.

References

  • General Chemistry: Principles and Modern Applications. Petrucci, Ralph H.; Harwood, William S.; Herring, F. Geoffrey. (2002). Prentice Hall: Upper Saddle River, NJ.
  • Chemistry, 9/e – Chang, R. (2006).