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What is a radical?
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All Flashcards in Topic 6.3
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6.3.112 cards
What is a radical?
A species with an **unpaired electron**, written with a dot (e.g. Cl•, •CH_{3}); very reactive.
What is homolytic fission?
A bond breaks **evenly** — **one electron goes to each** atom, forming two **radicals**.
What is heterolytic fission?
A bond breaks **unevenly** — **both electrons go to one** atom, forming **ions** (a cation and an anion).
Homolytic vs heterolytic — which makes radicals?
**Homolytic** fission makes radicals; **heterolytic** fission makes ions.
What is radical substitution?
An alkane reacts with a halogen in **UV light**, replacing an H atom with a halogen atom, via a radical chain.
What happens in the initiation step?
**UV light** breaks the halogen molecule by **homolytic** fission, e.g. Cl_{2} → 2 Cl•.
What happens in propagation?
A radical reacts to give a product **and a new radical**, so the chain continues (radical count unchanged).
Write the two propagation steps for CH_{4} + Cl_{2}.
Cl• + CH_{4} → •CH_{3} + HCl, then •CH_{3} + Cl_{2} → CH_{3}Cl + Cl•.
What happens in termination?
**Two radicals combine** into one molecule, removing radicals and **stopping** the chain (e.g. •CH_{3} + Cl• → CH_{3}Cl).
Why is UV light needed?
It supplies the energy to break the halogen bond **homolytically** and create the first radicals.
Why is it called a chain reaction?
Each propagation step **regenerates** a radical, so one initiation triggers many cycles (and a mixture of products).
How is a radical drawn?
With a **dot (•)** next to it, showing the single unpaired electron (e.g. Cl•).
Topic 6.3 study notes
Full notes & explanations for Electron sharing reactions
Chemistry exam skills
Paper structures, command terms & tips
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