General Formula: CₙH₂ₙ
- Compare to alkanes: CₙH₂ₙ₊₂ — alkenes have 2 fewer hydrogens
- This is because of the C=C double bond
- Example: Ethene = C₂H₄ (not C₂H₆ like ethane)
Unsaturated = Not Full of Hydrogen
- The double bond can "open up" and add more atoms
- The molecule isn't saturated with hydrogen — it could hold more!
- This makes alkenes much more reactive than alkanes
The First Four Alkenes (MUST memorise!):
1. Ethene (C₂H₄) — used to make poly(ethene) (plastic bags)
2. Propene (C₃H₆) — used to make poly(propene) (food containers)
3. Butene (C₄H₈) — can exist as different isomers
4. Pentene (C₅H₁₀) — multiple isomer positions possible
This deep dive covers What Makes Alkenes Special? 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 3 of 14 in this topic. Use this deep dive 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.
Quick recall flashcards
What are alkenes?
Unsaturated hydrocarbons containing a C=C double bond
How are alkenes produced?
By cracking long-chain alkanes from crude oil