What is the Difference Between Molecular Geometry and Electron Geometry

The key difference between molecular geometry and electron geometry is that molecular geometry is determined by the covalent bonds of the molecule, whereas electron geometry is determined by the electron pairs surrounding the central atom of a molecule.

Molecular geometry and electron geometry are important terms in general chemistry and make the basis for the determination of the properties of chemical compounds.

CONTENTS

1. Overview and Key Difference
2. What is Molecular Geometry 
3. What is Electron Geometry
4. Molecular Geometry and Electron Geometry in Tabular Form
5. Summary – Molecular Geometry vs Electron Geometry

What is Molecular Geometry?

Molecular geometry is the molecular structure of a compound given in the 3D arrangement of atoms. In other words, it is the 3D structural arrangement of the atoms in a particular molecule. Studying and identifying this spatial arrangement of atoms can help us determine the polarity of the compound, reactivity, phase of matter, color, magnetism, and biological activity.

Molecular geometry shows the shape of the molecule, bond, lengths, bond angles, torsional angles, and other geometric parameters that can determine the position of each atom. Typically, the bond angles between atoms only depend weakly on the rest of the molecule.

There are various different methods to determine molecular geometry, including spectroscopic methods such as diffraction methods, IR, microwave, and Raman spectroscopy. These methods can provide us with details about molecular geometry using vibrational and rotational absorbance that is detected by the spectroscopic technique. Moreover, we can get the molecular geometry of crystalline solids using X-ray crystallography, neutron diffraction, and electron diffraction. This determination is done based on the distance between nuclei and the concentration of the electron density. In addition, the position of atoms in the molecule can be determined by the nature of the chemical bonds through which it is connected to the neighboring atoms.

What is Electron Geometry?

Electron geometry is the arrangement of electron pairs around a central atom. In other words, electron geometry is the 3D structure of electron pairs (either bonding or non-bonding electron pairs) around a central atom. Usually, a lone electron pair or a non-bonding electron pair is a pair of valence electrons that are not shared between atoms in a covalent bond. A bond electron pair can be described as a pair of electrons that take part in a chemical bond.

Since electrons are negatively charged, electron pairs around a central atom are repelled by each other, making these electron pairs arrange around a particular atom in such a way that the repulsions they face is minimal. Therefore, bond angles slightly decrease accordingly.

Furthermore, if all the electron pairs around an atom are bond electron pairs, then the molecular geometry and electron geometry around this atom is the same. For example, a methane molecule has four bonds around the central carbon atom, and all the electrons around it are bond electrons. Therefore, the molecular geometry and electron geometry of this molecule is tetrahedral.

What is the Difference Between Molecular Geometry and Electron Geometry?

Molecular geometry and electron geometry are important terms in basic chemical principles and account for the determination of the chemical properties of molecules. Molecular geometry is the molecular structure of a compound given in the 3D arrangement of atoms whereas electron geometry can be defined as the arrangement of electron pairs around a central atom. The key difference between molecular geometry and electron geometry is that molecular geometry is determined by the covalent bonds of the molecule, whereas electron geometry is determined by the electron pairs surrounding the central atom of a molecule.

Summary – Molecular Geometry vs Electron Geometry

Molecular geometry and electron geometry determine the properties of a chemical compound. The key difference between molecular geometry and electron geometry is that molecular geometry is determined by the covalent bonds of the molecule, whereas electron geometry is determined by the electron pairs surrounding the central atom of a molecule.

Reference:

1. “Geometry of Molecules.” Chemistry LibreTexts, Libretexts.

Image Courtesy:

1. “Water molecule dimensions” By Booyabazooka – Image:Water_molecule_dimensions.png (CC BY-SA 3.0) via Commons Wikimedia
2. “Atomic Bond of Methane” (CC0) via Free SVG