This deep dive covers Deep Dive: Understanding Alkanes within Alkanes for GCSE Chemistry. Topic 38: Alkanes It is section 3 of 12 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
🔬 Deep Dive: Understanding Alkanes
The General Formula: CₙH₂ₙ₊₂
- n = number of carbon atoms
- Plug in n to find the formula for any alkane
- Example: n=3 → C₃H₂₍₃₎₊₂ = C₃H₈ (propane)
Why "Saturated"?
- Alkanes have ONLY single bonds between carbons
- This means every carbon is bonded to as many hydrogens as possible
- The molecule is "saturated" with hydrogen — can't hold any more!
- Compare to alkenes which have C=C double bonds (unsaturated)
The First Four Alkanes (MUST memorise!):
| Name | Formula | Carbons | State at room temp |
|---|---|---|---|
| Methane | CH₄ | 1 | Gas |
| Ethane | C₂H₆ | 2 | Gas |
| Propane | C₃H₈ | 3 | Gas |
| Butane | C₄H₁₀ | 4 | Gas |
Naming Pattern: Meth (1), Eth (2), Prop (3), But (4), Pent (5), Hex (6)... + "ane"
Properties of Alkanes:
- Longer chains = higher boiling point (stronger forces between molecules)
- First four are gases, then liquids, then waxy solids
- Don't mix with water (immiscible)
- Burn well in oxygen (good fuels!)
- Generally unreactive — only combustion and reactions with halogens
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.
Quick recall flashcards
Formula for ethane?
C₂H₆
Formula for butane?
C₄H₁₀