This how it works covers Why Alkanes Are Saturated and Relatively Unreactive within Alkanes for GCSE Chemistry. Topic 38: Alkanes It is section 5 of 12 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
⚙️ Why Alkanes Are Saturated and Relatively Unreactive
The term "saturated" has a precise chemical meaning: every carbon atom forms the maximum possible number of bonds with hydrogen atoms. Because all C-C bonds are single bonds, there is no double bond available to participate in addition reactions.
Why single bonds make alkanes less reactive:
- Single C-C bonds are strong and difficult to break without a catalyst or high energy
- There is no double bond to "open up" and accept additional atoms (compare to alkenes)
- As a result, alkanes only undergo combustion with oxygen (burning) and substitution reactions with halogens (in UV light)
- Alkenes are far more reactive because the C=C double bond can break open and allow addition reactions to occur
Why boiling point increases with chain length:
Longer chains have more electrons and therefore stronger forces between molecules. More energy is needed to overcome these forces, giving longer alkanes higher boiling points. Methane is a gas at room temperature; waxes (C20+) are solid.
Practice questions for Alkanes
What is the general formula for the alkane homologous series?
Explain why the boiling point of alkanes increases as the chain length increases.