Introduction
Free-radicals are neutral species that contain unpaired electrons.
Reactivity 3.3.1 - A radical is a molecular entity that has an unpaired electron. Radicals are highly reactive.
- Identify and represent radicals, e.g. ●CH3 and Cl●.
Guidance
Tools and links
- Structure 2.1 - How is it possible for a radical to be an atom, a molecule, a cation or an anion? Consider examples of each type.
Reactivity 3.3.2 - Radicals are produced by homolytic fission, e.g. of halogens, in the presence of ultraviolet (UV) light or heat.
- Explain, including with equations, the homolytic fission of halogens, known as the initiation step in a chain reaction.
Guidance
- The use of a single-barbed arrow (fish-hook) to show the movement of a single electron should be covered.
Tools and links
- Reactivity 1.2 - Why do chlorofluorocarbons (CFCs) in the atmosphere break down to release chlorine radicals but typically not fluorine radicals?
- Structure 2.2 - What is the reverse process of homolytic fission?
- Structure 2.2 - Chlorine radicals released from CFCs are able to break down ozone, O3, but not oxygen, O2, in the stratosphere. What does this suggest about the relative strengths of bonds in the two allotropes?
Reactivity 3.3.3 - Radicals take part in substitution reactions with alkanes, producing a mixture of products.
- Explain, using equations, the propagation and termination steps in the reactions between alkanes and halogens.
Guidance
- Reference should be made to the stability of alkanes due to the strengths of the C–C and C–H bonds and their essentially non-polar nature.
Tools and links
- Reactivity 2.2 - Why are alkanes described as kinetically stable but thermodynamically unstable?
In Reactivity 3.3 - Electron sharing reactions