The C=C double bond is the source of alkene reactivity. The double bond (C=C) means two pairs of electrons are shared between the carbon atoms. One of these pairs is easier to break and provides the reaction site.
How addition reactions work:
- A small molecule (H₂, Br₂, H₂O) approaches the C=C double bond
- One bond of the double bond opens up
- Each atom from the added molecule bonds to one of the two carbons
- The result is a single bond between those carbons — a saturated product
- This is why the reaction is called an addition reaction — atoms are added across the double bond
Why alkanes don't do this: Alkanes only have single C-C bonds, which are much stronger and require significant energy (or UV light) to break. There is no reactive double bond available. This is why alkenes are useful for making polymers — their double bonds can react — while alkanes are mainly used as fuels.
This how it works covers Why Alkenes Are More Reactive Than Alkanes within Alkenes for GCSE Chemistry. Revise Alkenes in Organic Chemistry for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 4 of 14 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Practice questions for Alkenes
What is the general formula for alkenes?
Explain what is meant by the term 'unsaturated' when applied to alkenes.