The main difference between homolytic and heterolytic bond fission is that in homolytic bond fission, one bond electron is given to each fragment, whereas in heterolytic bond fission, two bond electrons are given to one fragment, and the other fragment receives none of the electrons.
Chemical bonds form by the interaction between chemicals. They form either covalent bonds or ionic bonds. These bond formation takes place to gain stability by the reactants. In bond formation, electrons are either given off or taken in or are shared with the species of chemicals involved in bond formation. But sometimes, these bonds can break. Fission is the destruction of a covalent chemical bond. It divides one molecule into two parts. Fission is of two types: homolytic fission and heterolytic fission. Homolytic fission involves the formation of two equal moieties, whereas heterolytic fission involves the formation of two unequal moieties.
Key Areas Covered
1. What is Homolytic Fission
– Definition, Features, Energy
2. What is Heterolytic Bond Fission
– Definition, Features, Energy
3. Difference Between Homolytic and Heterolytic Bond Fission
– Comparison of Key Differences
Key Terms
Bond Homolysis, Homolytic Bond Cleavage, Homolytic Bond Fission, Heterolytic Bond Fission
What is Homolytic Fission
Homolytic fission is the dissociation of a chemical bond, forming two equal fragments. In a covalent chemical bond, there are two electrons in the bond. In a type of fission like this, the two fragments get one electron each. When the bond dissociation happens in a neutral molecule, two fragments get one electron, each forming two free radicals. The energy required for homolytic bond dissociation, whether it is absorbed or released, is known as homolytic bond dissociation energy. The homolytic bond fission happens under specific conditions, such as in the presence of heat and UV radiation.
Homolytic bond fission, also known as bond homolysis or homolytic bond cleavage, typically requires a large amount of energy. This is why this fission happens in the following instances:
- The pyrolysis of carbon compounds at extremely high temperatures in the absence of oxygen.
- Overcoming the bond dissociation energy for heterolytic fission by subjecting the molecule to the required amount of heat.
- Subjecting the molecule to ultraviolet radiation, which corresponds to the ultraviolet region of the electromagnetic spectrum.
Figure 1: Heterolysis of a Chemical Bond
In certain instances, homolytic bond fusion only requires a small amount of heat. One example is the oxygen-oxygen bond in peroxides, which is relatively weak and has a low activation energy, requiring less heat.
What is Heterolytic Bond Fission
In heterolytic bond fission, one fragment of the molecule gets two electrons, whereas the other fragment of the molecule gets none of the electrons. We call this process heterolysis or heterolytic cleavage. Here, the covalent bond between two chemical species breaks down in a nonsimilar way. This results in one fragment getting two electrons, whereas the other fragment gets non of the electrons.
When a molecule with a neutrally charged molecule is subject to heterolytic fission, one of the resulting fragments will have a negative charge, whereas the other fragment will have a positive charge. The positively charged fragment is also called the cation. This fragment is the fragment that does not get any of the electrons in the bond fission. The other molecule is the anion, and this molecule contains both the electrons of the previous covenant bond after the heterolytic bond fission.
In heterolytic bond fission, the fragment that gets both electrons has the highest electronegativity out of the two fragments, obtaining a negative charge. The more electropositive element contains no electrons of the bond; hence it gets a positive charge. Moreover, heterolytic bond dissociation energy is the energy required to break down the bond in the heterolytic bond fission process.
Difference Between Homolytic and Heterolytic Bond Fission
Definition
Homolytic fission is the dissociation of a chemical bond, forming two equal fragments, while heterolytic fission is the dissociation of a chemical bond where one fragment of the molecule gets two electrons, and the other fragment of the molecule gets none of the electrons.
Bond Electrons
In homolytic fission, each product gets one electron, whereas in heterolytic fission, only one product gets two electrons, and the other product gets no electrons.
Products
Homolytic fission involves the formation of two equal products, while heterolytic fission involves the formation of unequal products.
Energy
In homolytic fission, the energy that is given out or taken in is knowns as homolytic bond dissociation energy, whereas in heterolytic fission, this energy is known as heterolytic bond dissociation energy.
Conclusion
Fission is the destruction of a covalent chemical bond. In brief, there are two types of fission according to bond formation and electron distribution. heterolytic bond fission. The main difference between homolytic and heterolytic bond fission is that in homolytic bond fission, one bond electron is given to each fragment, whereas in heterolytic bond fission, two bond electrons are given to one fragment, and the other fragment receives none of the electrons.
Reference:
1. “Homolytic & Heterolytic Fission.” Byju’s.
Image Courtesy:
1. “Heterolysis (Chemistry)” By Jürgen Martens – Jürgen Martens (CC BY-SA 3.0) via Commons Wikimedia
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