Difference Between Homolytic and Heterolytic Fission with Examples
Understanding homolytic and heterolytic fission is essential in chemistry and helps students make sense of how chemical bonds break during reactions. This concept forms the basis for many topics in organic chemistry and is important for building strong fundamentals.
What is Homolytic and Heterolytic Fission in Chemistry?
Homolytic and heterolytic fission describe how covalent bonds can break in different ways. In homolytic fission, a bond breaks so both atoms take one electron each, creating free radicals.
In heterolytic fission, one atom takes both electrons from the bond, forming charged ions. These ideas are widely used in areas like types of chemical reactions, covalent bonding, and organic reaction mechanisms.
Homolytic Fission Explained
Homolytic fission occurs when a covalent bond splits evenly, with each atom taking one electron from the bonded pair. This process forms two neutral species, called free radicals, which have an unpaired electron.
Homolytic fission typically happens in non-polar solvents, at high temperatures, or with UV light present.
For example, when a chlorine molecule (Cl2) absorbs UV light, it splits as follows:
Cl2 → Cl• + Cl•
Here, each chlorine atom ends up with one unpaired electron, forming two chlorine radicals.
Heterolytic Fission Explained
Heterolytic fission is when a covalent bond breaks unevenly, and both electrons go to one of the bonded atoms. This results in the formation of a positive ion (cation) and a negative ion (anion).
Heterolytic fission is more common when there is a big difference in electronegativity between the atoms, or when the reaction happens in a polar solvent.
A classic example is the splitting of hydrogen chloride (HCl):
H–Cl → H+ + Cl–
Here, the chlorine atom takes both electrons, becoming a chloride ion (Cl–), while the hydrogen atom becomes a proton (H+).
Homolytic vs Heterolytic Fission: Key Differences
| Criteria | Homolytic Fission | Heterolytic Fission |
|---|---|---|
| Electron Movement | Each atom gets one electron | Both electrons go to one atom |
| Particles Formed | Free radicals (neutral) | Ions (cation and anion) |
| Common Conditions | High energy, UV light, non-polar solvent | Polar solvent, big electronegativity difference |
| Example | Cl2 → Cl• + Cl• | HCl → H+ + Cl– |
| Uses in Chemistry | Radical reactions | Ionic (SN1/SN2) reactions |
Step-by-Step Reaction Example
1. Take a chlorine molecule and expose it to ultraviolet (UV) light.2. The Cl–Cl bond absorbs energy and splits so that each Cl atom gets one electron.
3. The products are two chlorine radicals: Cl2 → Cl• + Cl•
4. These free radicals can now start chain reactions, like in the chlorination of methane.
Uses of Homolytic and Heterolytic Fission in Real Life
Both types of bond fission are common in everyday chemistry. Homolytic fission is important in making plastics and medicines because it helps form free radicals needed for polymerisation. Heterolytic fission is common in organic reactions involving ions, such as making drugs, detergents, and solvents in industries.
Relation with Other Chemistry Concepts
Homolytic and heterolytic fission link with many other chemistry topics such as free radicals, carbocations and carbanions, and organc reaction mechanisms. They also help us understand the basic nature of a covalent bond and its behaviour under different conditions.
Frequent Related Errors
- Mixing up homolytic with heterolytic fission, especially during reaction mechanism steps.
- Forgetting that radicals from homolytic fission are neutral, not ionic.
- Assuming heterolytic fission needs only energy, when solvent and atom properties matter a lot.
- Ignoring the effect of electronegativity and reaction medium.
Lab or Experimental Tips
A quick trick to remember: if atoms are similar (like Cl–Cl), homolytic fission is more likely. If they’re very different (like H–Cl), expect heterolytic fission. Vedantu teachers often demonstrate radical formation using simple colored light or easy-to-understand models for better visualization.
Try This Yourself
- Write a reaction showing the homolytic fission of bromine (Br2).
- Explain, in your words, what products you get after heterolytic fission of methyl chloride (CH3Cl).
- List one everyday application for each type of fission.
Final Wrap-Up
We explored homolytic and heterolytic fission—their definitions, mechanisms, differences, and real-life relevance. These concepts help students grasp reaction pathways and understand product formation in organic chemistry. For more easy explanations, topic notes, and live lessons, visit Vedantu online learning sessions.
FAQs on Homolytic and Heterolytic Fission in Organic Chemistry
1. What is homolytic fission?
Homolytic fission is the breaking of a covalent bond in which each atom takes away one electron, forming two free radicals.
• Occurs in non-polar solvents or under the influence of heat or light.
• Example: Cl–Cl → 2 Cl· (free radicals).
2. What is heterolytic fission?
Heterolytic fission is the cleavage of a covalent bond where one atom takes both electrons, resulting in a cation and an anion.
• Produces ions instead of free radicals.
• Example: H–Cl → H⁺ (cation) + Cl⁻ (anion).
3. What is the key difference between homolytic and heterolytic fission?
The main difference is:
• Homolytic fission produces two free radicals by equal sharing of electrons.
• Heterolytic fission produces a cation and an anion by unequal sharing of electrons.
4. Can you give an example of homolytic fission in chemistry?
Yes. Chlorine molecule under ultraviolet light undergoes homolytic fission:
Cl–Cl → Cl· + Cl·
Here, each chlorine atom takes one electron and forms a free radical.
5. What products result from heterolytic bond fission?
Heterolytic bond fission produces a positively charged ion (cation) and a negatively charged ion (anion).
• Example: H–Cl → H⁺ + Cl⁻
6. In which reactions is homolytic fission more common?
Homolytic fission commonly occurs in free radical reactions such as:
• Halogenation of alkanes
• Polymerization
• Thermal decomposition
These processes usually require heat, light, or a radical initiator.
7. Why is understanding bond fission important in organic reaction mechanisms?
Bond fission knowledge is essential because:
• It helps explain how intermediates like free radicals, carbocations, and carbanions are formed.
• Understanding the type of fission predicts product types and reaction pathways in organic chemistry.
8. How can you distinguish between the products of homolytic and heterolytic fission?
Homolytic fission forms free radicals (neutral, unpaired electrons), while heterolytic fission forms an ion pair (cation and anion).
• Look for unpaired electrons (radicals) vs. charged particles (ions) in the products.
9. What factors favor heterolytic fission over homolytic fission?
Heterolytic fission is favored by:
• Polar solvents
• Polar bonds (large electronegativity difference)
• Presence of electron-withdrawing or donating groups
• Low temperature and mild conditions
10. Are free radicals always unstable? Can they ever be stabilized?
Free radicals are generally unstable due to unpaired electrons, but they can be stabilized by:
• Resonance (delocalization of the unpaired electron)
• Inductive effect from adjacent alkyl groups
• Aromaticity or conjugation in the molecule
11. Can both homolytic and heterolytic fission occur in the same molecule during a reaction pathway?
Yes, some organic reaction mechanisms can involve both homolytic and heterolytic fission steps, depending on the specific reaction conditions and intermediates formed.
12. Why does a molecule prefer homolytic fission over heterolytic fission under certain conditions?
Homolytic fission is favored under conditions like high temperature, UV light, or in non-polar solvents because these provide enough energy for equal electron sharing, especially in non-polar or weakly polar bonds.
