Saturated – IGCSE Chemistry Definition
IGCSE Chemistry definition of saturated: a molecule containing only single C–C bonds. Covers alkanes, the bromine test, and exam tips for Cambridge 0620.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
The saturated/unsaturated distinction is fundamental to organic chemistry at IGCSE. It determines what type of reactions a compound undergoes and appears in multiple choice, structured questions, and practical scenarios.
The 0620 definition
A saturated compound contains only single covalent bonds between carbon atoms. It has no C=C double bonds.
The carbon atoms are “saturated” with hydrogen — they are bonded to the maximum number of hydrogen atoms possible for that carbon skeleton.
Saturated hydrocarbons: alkanes
Alkanes are the saturated homologous series. Their general formula is CₙH₂ₙ₊₂.
| Alkane | Formula | Structure |
|---|---|---|
| Methane | CH₄ | All single bonds |
| Ethane | C₂H₆ | C−C single bond |
| Propane | C₃H₈ | C−C−C chain |
| Butane | C₄H₁₀ | C−C−C−C chain |
Compare with alkenes (CₙH₂ₙ) — alkenes have two fewer hydrogen atoms because the C=C double bond replaces two C−H bonds.
Reactions of saturated compounds
Because there is no double bond to open, saturated compounds cannot undergo addition reactions. Instead, they undergo:
- Substitution reactions: an atom or group replaces a hydrogen atom
- CH₄ + Cl₂ → CH₃Cl + HCl (in UV light)
- Combustion: burning in air/oxygen
- CH₄ + 2O₂ → CO₂ + 2H₂O
The bromine water test
| Compound type | Result with bromine water |
|---|---|
| Saturated (e.g. hexane) | Bromine water stays orange-brown |
| Unsaturated (e.g. hexene) | Bromine water decolourised |
This test distinguishes alkanes from alkenes and is one of the most commonly examined practical tests.
Worked exam question
Ethane and ethene both contain two carbon atoms. (a) State which is saturated. [1] (b) Describe a chemical test to distinguish between them. [2]
Mark scheme
(a) Ethane [1]
(b) Add bromine water [1]; ethene decolourises the bromine water (from orange to colourless) but ethane does not [1]
Common exam mistakes
- Saying saturated means “full of carbon” — it means all C−C bonds are single bonds / no C=C double bonds.
- Confusing saturated hydrocarbons with saturated solutions — completely different concepts.
- Stating that saturated compounds do not react at all — they undergo substitution and combustion, just not addition.
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