This document discusses alkanes and their chemical properties and reactions. Alkanes are chemically inert due to their saturated carbon bonds and similar electronegativities of carbon and hydrogen. They can only undergo substitution reactions under high temperatures or with reactive reagents like radicals. The mechanism for substituting alkanes to form alkyl halides is a free radical substitution reaction. When writing free radical mechanisms, the name of the mechanism should be included and a series of chemical equations shown without descriptive text. Common errors include using the wrong arrows, forgetting initiators like UV light or heat, using molecular formulas instead of structural formulas, and substituting the wrong halogen.

1. Alkanes

2. Alkanes
For each homologous series, we will focus mainly on:
1. Physical properties (trend)
2. Chemical properties (reactions and mechanism)

3. Chemical Properties
- Alkanes are chemically inert since:
1. all the carbons are saturated (have four bonds)
2. there are no electron rich/ poor regions due to the
similar electronegativities of C and H.
- Alkanes can only undergo reactions under high temp
(combustion) or with very reactive reagent (radicals)

4. Chemical Properties
- The mechanism for the substitution of alkanes to give
alkyl halides is free radical substitution
- Not ‘substitution’, ‘free radical reaction’ or ‘free
substitution’ or ‘FRS’

5. Writing
Free Radical Mechanism
When writing mechanisms:
1. It is a good practice to write the name of the
mechanism whether or not the question asks for it.
2. You just need to show the series of equations/ arrows.
There is no need for descriptions i.e. the chlorine
molecule undergoes homolytic cleavage to give two
chlorine atoms/ radicals.

6. Writing
Free Radical Mechanism
Error 1: Wrong arrows

7. Writing
Free Radical Mechanism
Error 2: Forget to put ‘UV light’ or ‘heat’

8. Writing
Free Radical Mechanism
Error 3: Use of molecular formula.

9. Writing
Free Radical Mechanism
Error 4: Wrong halogen.
Under exam conditions, students sometimes use the wrong
halogen (i.e. use Cl2 when qns asks for Br2)
This happens when they regurgitate what they have
memorised blindly

10. Writing
Free Radical Mechanism
Error 4: Wrong halogen.
Under exam conditions, students sometimes use the wrong
halogen (i.e. use Cl2 when qns asks for Br2)
This happens when they regurgitate what they have
memorised blindly