4.3 Alkanes

REVISION NOTES

IGCSE Edexcel Chemistry

4.3 Alkanes

4.3.1 Know the general formula for alkanes

General formula for alkanes:

C_nH_2n+2

EXAMPLE

Ethane is a type of alkane with the formula C₂H₆

4.3.2 Explain why alkanes are classified as saturated hydrocarbons

ALKANES

Contain only single bonds (C–C and C–H)
Each carbon has 4 single bonds around it, which is the maximum number of bonds it can form
Therefore, the carbons are saturated

4.3.3 Understand how to draw the structural and displayed formulae for alkanes with up to five carbon atoms in the molecule, and to name the unbranched-chain isomers

4.3.4 Describe the reactions of alkanes with halogens in the presence of ultraviolet radiation, limited to mono-substitution

knowledge of reaction mechanisms is not required

Reaction of Alkanes with Halogens

UV

alkane + halogen → halogenoalkane + hydrogen halide

As alkanes are saturated, they undergo substitution reaction
The reaction only happens in presence of ultraviolet (UV) radiation
It is a mono-substitution reaction:
- One of the hydrogen is substituted by the halogen

Product names:
fluoro / chloro / bromo / iodo [alkane name]

+ hydrogen fluoride / chloride / bromide / iodide

UV

C₂H₆ + Br₂ → C₂H₅Br + HBr