Hydrocarbon – IGCSE Chemistry Definition
IGCSE Chemistry definition of hydrocarbon: a compound containing only carbon and hydrogen. Covers types, examples, combustion, 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 term hydrocarbon is foundational in organic chemistry. It defines the simplest organic molecules and links directly to fossil fuels, combustion, and cracking. Paper 1 often tests whether candidates can identify which molecule from a list is a hydrocarbon.
The 0620 definition
A hydrocarbon is a compound that contains only hydrogen and carbon atoms — no other elements.
Types of hydrocarbon
| Type | Bonding | General formula | Example |
|---|---|---|---|
| Alkane | All single C−C bonds (saturated) | CₙH₂ₙ₊₂ | Methane, CH₄ |
| Alkene | At least one C=C double bond (unsaturated) | CₙH₂ₙ | Ethene, C₂H₄ |
Hydrocarbons as fuels
Most fossil fuels (natural gas, petroleum, coal) are hydrocarbons or mixtures of hydrocarbons. When they burn:
Complete combustion (excess oxygen): Hydrocarbon + O₂ → CO₂ + H₂O
Incomplete combustion (limited oxygen): Hydrocarbon + O₂ → CO (or C) + H₂O
Which of these are hydrocarbons?
| Compound | Formula | Hydrocarbon? | Reason |
|---|---|---|---|
| Methane | CH₄ | Yes | Only C and H |
| Ethanol | C₂H₅OH | No | Contains oxygen |
| Ethene | C₂H₄ | Yes | Only C and H |
| Ethanoic acid | CH₃COOH | No | Contains oxygen |
| Propane | C₃H₈ | Yes | Only C and H |
The test is simple: does the molecule contain any element other than C and H? If yes, it is not a hydrocarbon.
Fractional distillation of hydrocarbons
Crude oil is a mixture of hydrocarbons separated by fractional distillation. Shorter-chain hydrocarbons have lower boiling points and are collected near the top of the fractionating column.
Worked exam question
Define the term hydrocarbon. Give one example of a saturated hydrocarbon and one example of an unsaturated hydrocarbon. [3]
Mark scheme
A compound containing only carbon and hydrogen / only C and H atoms [1]; saturated example: any alkane, e.g. methane CH₄ / ethane C₂H₆ / propane C₃H₈ [1]; unsaturated example: any alkene, e.g. ethene C₂H₄ / propene C₃H₆ [1]
Common exam mistakes
- Including molecules with oxygen (e.g. ethanol) as hydrocarbons — the definition requires only carbon and hydrogen.
- Defining a hydrocarbon as “a molecule containing carbon and hydrogen” without saying “only” — without “only,” ethanol would qualify.
- Confusing hydrocarbon with organic compound — all hydrocarbons are organic compounds, but not all organic compounds are hydrocarbons (alcohols, carboxylic acids contain O).
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