What is the Difference Between Homolysis and Heterolysis

The key difference between homolysis and heterolysis is that homolysis is the breakdown of a chemical compound into two chemically equal parts, whereas heterolysis is the breakdown of a chemical compound into two chemically different parts.

We can use bond dissociation energies of chemical compounds to describe the homolysis and heterolysis processes. Bond dissociation energy is a measure of the strength of a chemical bond. A bond can be dissociated in a homolytic manner or a heterolytic manner. Bond dissociation energy is defined as the standard enthalpy change when a chemical bond is cleaved via homolysis.

CONTENTS

1. Overview and Key Difference
2. What is Homolysis 
3. What is Heterolysis
5. Homolysis vs Heterolysis in Tabular Form
6. Summary

What is Homolysis?

Homolysis is the cleavage of a chemical bond in a way that it gives two chemically equal parts of the chemical compound. A chemical bond (covalent bond) contains two electrons. In this form of fission, each of the fragments gets one unpaired electron. When this bond dissociation occurs in a neutral molecule that has an even number of electrons, it forms two equal free radicals.

Homolytic bond dissociation energy is the amount of energy required to dissociate a chemical bond via hemolysis. Hemolysis of a chemical bond is the symmetric cleavage of the bond-forming two radicals, not two ions. Here, the bond electrons between the atoms are divided into two halves and are taken by the two atoms. For example, the homolytic cleavage of a sigma bond forms two radicals having one unpaired electron per radical.

What is Heterolysis?

Heterolysis is the cleavage of a chemical bond in a way that it gives two chemically different parts of the chemical compound. Heterolytic fission is the dissociation of a chemical bond and forming two unequal fragments. A chemical bond (covalent bond) contains two electrons. In this form of fission, one fragment gets both bond electron pairs while the other fragment gets none of the bond electrons.

Heterolytic bond dissociation energy is the amount of energy required to clave a chemical bond via heterolysis. Heterolysis is the cleavage of a chemical bond in an asymmetric manner. Heterolysis forms cations and anions since, in heterolysis, the bond electron pair is taken by the electronegative atom (it is converted into the anion), while the other atom takes no electrons (it forms the cation).

What is the Difference Between Homolysis and Heterolysis?

Homolysis and heterolysis are chemical processes that are opposite to each other. The key difference between homolysis and heterolysis is that homolysis is the breakdown of a chemical compound into two chemically equal parts, whereas heterolysis is the breakdown of a chemical compound into two chemically different parts. Moreover, homolytic bond dissociation energy determines the energy required for homolysis to occur whereas heterolytic bond dissociation energy determines the energy required for heterolysis to occur.

The following infographic summarizes the difference between homolysis and heterolysis in tabular form.

Summary – Homolysis vs Heterolysis

Homolysis and heterolysis are chemical processes that are opposite to each other. The key difference between homolysis and heterolysis is that homolysis is the breakdown of a chemical compound into two chemically equal parts, whereas heterolysis is the breakdown of a chemical compound into two chemically different parts.

Reference:

1.“Homolysis.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Homolysis (Chemistry)” By Jürgen Martens – Jürgen Martens (Public Domain) via Commons Wikimedia
2. “Heterolysis (Chemistry)” By Jürgen Martens – Jürgen Martens (CC BY-SA 3.0) via Commons Wikimedia