The key difference between localized and delocalized electrons is that localized electrons are located between atoms, whereas delocalized electrons are located above and below atoms.

In general chemistry, localized electrons and delocalized electrons are terms that describe chemical structures of chemical compounds. Localized electrons are the bonding electrons in molecules while delocalized electrons are nonbonding electrons that occur as electron clouds above and below the molecule.

CONTENTS

1. Overview and Key Difference
2. What are Localized Electrons
3. What are Delocalized Electrons
4. Side by Side Comparison – Localized vs Delocalized Electrons in Tabular Form
5. Summary

What are Localized Electrons?

Localized electrons are the bonding electrons in chemical compounds. These electrons are located between atoms where sigma bonds can be found. Sigma bonds are the bonds formed by the axial overlapping of half-filled atomic orbitals of atoms.

Therefore, localized electrons occur in covalent compounds having covalent chemical bonds. These localized electrons belong to two particular atoms, in contrast to delocalized electrons, which are common to all the atoms in the molecule. Localized electrons are shared between atoms forming covalent bonds, coordination bonds, etc.

What are Delocalized Electrons?

Delocalized electrons are the nonbonding electrons in chemical compounds. This term refers to electrons that are not associated with a single atom or a covalent bond. However, the term delocalized electron has different meanings in different fields. For example, in organic chemistry, delocalized electrons are in the resonance structures of conjugated systems in aromatic compounds. In solid-state physics, delocalized electrons are the free electrons that facilitate electrical conduction. Moreover, quantum physics use the term delocalized electrons to refer to molecular orbital electrons that have extended over several atoms.

Figure 01: Benzene, (delocalization of the electrons is indicated by the circle)

The benzene ring is the simplest example of an aromatic system having delocalized electrons. There are six pi electrons in the benzene molecule; we often indicate these graphically using a circle.  This circle means the pi electrons are associated with all the atoms in the molecule. This delocalization makes the benzene ring to have chemical bonds with similar bond lengths.

What is the Difference Between Localized and Delocalized Electrons?

We use terms localized and delocalized electrons under the branch of general chemistry, regarding the chemical structure of compounds. A localized atom is an electron that belongs to a particular atom while a delocalized electron is an electron not associated with any single atom or a single covalent bond. The key difference between localized and delocalized electrons is that localized electrons are located between atoms, whereas delocalized electrons are located above and below the atoms. In other words, localized electrons are confined to a particular region between two atoms while delocalized electrons are spread over several atoms.

Moreover, another significant difference between localized and delocalized electrons is that the localized electrons are associated with particular atoms in a compound while the delocalized electrons are associated with all the atoms in the molecule. Besides, localized electrons are graphically indicated by straight lines, while delocalized electrons are graphically indicated by circles.

The following table summarizes the differences between localized and delocalized electrons.

Summary – Localized and Delocalized electron

The terms localized and delocalized electrons are discussed under general chemistry. The key difference between localized and delocalized electrons is that localized electrons are located between atoms, whereas delocalized electrons are located above and below the atoms. Moreover, delocalized electrons are associated with particular atoms in a compound while the delocalized electrons are associated with all the atoms in the molecule.

Reference:

1. “Localized and Delocalized Lone Pairs and Bonds.” Chemistry Steps, 22 Aug. 2020, Available here.
2. “Delocalized Electron.” Wikipedia, Wikimedia Foundation, 13 July 2020, Available here.

Image Courtesy:

1. “Benz4” By Selfmade by cacycle, Leyo – Own work (CC BY-SA 3.0) via Commons Wikimedia

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