Saturated & Unsaturated Compounds
Section: 11. Organic Chemistry | Syllabus: Cambridge IGCSE Chemistry (0620)
Saturated Compounds
A saturated compound has molecules in which all the carbon-carbon bonds are single bonds.
- Alkanes are the saturated hydrocarbons: only C-C and C-H single bonds are present
- Each carbon atom bonds to the maximum possible number of hydrogen atoms
- General formula: CnH2n+2
Unsaturated Compounds
An unsaturated compound has molecules in which one or more carbon-carbon bonds are not single bonds - that is, they contain a C=C double bond.
- Alkenes are the unsaturated hydrocarbons: they contain at least one C=C double bond
- Because they have fewer hydrogen atoms than the corresponding alkane, unsaturated compounds can undergo addition reactions
- General formula: CnH2n
Whether a compound is saturated or unsaturated can be tested using aqueous bromine (the bromine water test) - see the Alkenes topic for full details of this test and of addition reactions.
Worked Example
- Question (based on a real exam question): which statement about alkenes is correct - (A) alkenes are saturated molecules containing a C=C double bond, (B) alkenes have general formula CnH2n+2, (C) alkenes react with aqueous bromine to give a colour change from brown to colourless, (D) alkenes are manufactured from larger alkene molecules by combustion?
- Answer: C. Statement A is self-contradictory (a C=C double bond makes a compound unsaturated, not saturated); statement B gives the alkane formula, not the alkene formula; statement D confuses cracking (alkane → alkene) with combustion.
Common Mistakes
- ❌ Describing a compound with a C=C double bond as "saturated"
- ✓ the presence of a C=C double bond is exactly what makes a compound unsaturated - "saturated" means single carbon-carbon bonds only
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