Hydrocarbons and the alkane series

Hydrocarbons are compounds containing only carbon and hydrogen. They are divided into:

• Aliphatic open-chain: saturated (alkanes, CₙH₂ₙ₊₂), unsaturated with a double bond (alkenes, CₙH₂ₙ) or a triple bond (alkynes, CₙH₂ₙ₋₂).
• Cyclic aliphatic: saturated cycloalkanes (CₙH₂ₙ) such as cyclohexane.
• Aromatic: containing a benzene ring, such as benzene and toluene.

The alkanes (paraffins)

Alkanes form a homologous series of general formula CₙH₂ₙ₊₂:

• Methane CH₄ · ethane C₂H₆ · propane C₃H₈ · butane C₄H₁₀ · pentane C₅H₁₂ · hexane C₆H₁₄.
• What is observed in the series: each member differs from the next by a –CH₂– unit (14 in molecular mass), they share one general formula and similar chemical properties, while physical properties change gradually with mass.
• Importance and sources: alkanes are the main constituents of natural gas and of the light fraction of petroleum, used as fuels and as raw material for many chemicals.