| Series | General Formula | Example (n=3) |
|---|---|---|
| Alkanes | CₙH₂ₙ₊₂ | Propane (C₃H₈) |
| Alkenes | CₙH₂ₙ | Propene (C₃H₆) |
| Alcohols | CₙH₂ₙ₊₁OH | Propan-1-ol (C₃H₇OH) |
| Carboxylic acids | CₙH₂ₙ₊₁COOH | Propanoic acid |
Properties of a Homologous Series
- Same general formula
- Same functional group → same chemical properties
- Differ by -CH₂- between consecutive members
- Gradual trend in physical properties (e.g. Boiling point increases with chain length due to stronger London dispersion forces)
Physical Trend
Why Boiling Point Increases Along a Series
As chain length increases by each successive -CH₂- unit:
- The molecule has a greater molecular mass and more total electrons.
- The electron cloud is more polarisable, resulting in stronger London dispersion forces.
- More thermal energy is required to overcome these intermolecular forces, so boiling point increases.
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