Chemistry

8.1 - Hydrocarbons & Homologous Series

5 min

Hydrocarbons

The first four alkanes

Homologous series & formula

Saturated compounds

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Hydrocarbons and homologous series

Organic chemistry is the chemistry of compounds that contain carbon.
A hydrocarbon is a compound made up of hydrogen and carbon only.
- Methane (CH₄) is a hydrocarbon. Ethanol is not, because it contains oxygen.

Why there are so many carbon compounds

A carbon atom forms four covalent bonds, and it bonds readily to other carbon atoms.
Carbon atoms join end to end into chains (short or long) and into rings.
Each carbon uses its remaining bonds to join to hydrogen atoms or atoms of other elements.

Homologous series

A homologous series is a family of similar compounds.
Members of the same homologous series share:
- The same general formula.
- Each member differs from the next by a CH₂ unit.
- A gradual change in physical properties (melting and boiling points rise as molecules get bigger, because larger molecules have stronger intermolecular forces).
- Similar chemical properties (they react in similar ways).

key terms

TermDefinition

HydrocarbonA compound made of hydrogen and carbon atoms only.

Homologous seriesA family of compounds with the same general formula and similar chemical properties. Each member differs from the next by a CH₂ unit.

end of notes

Key points to remember

Hydrocarbons and homologous series

Organic chemistry is the chemistry of compounds that contain carbon.

A hydrocarbon is a compound made up of hydrogen and carbon only.

Methane (CH₄) is a hydrocarbon. Ethanol is not, because it contains oxygen.

Why there are so many carbon compounds

A carbon atom forms four covalent bonds, and it bonds readily to other carbon atoms.

Carbon atoms join end to end into chains (short or long) and into rings.

Each carbon uses its remaining bonds to join to hydrogen atoms or atoms of other elements.

Homologous series

A homologous series is a family of similar compounds.

Members of the same homologous series share:

The same general formula.
Each member differs from the next by a CH₂ unit.
A gradual change in physical properties (melting and boiling points rise as molecules get bigger, because larger molecules have stronger intermolecular forces).
Similar chemical properties (they react in similar ways).