Alkenes are represented with the general molecular formula

The homologous series of alkenes are unsaturated hydrocarbons that contain exactly one carbon-carbon double bond (C=C). Their general molecular formula is \(\text{C}_n\text{H}_{2n}\), where n is the number of carbon atoms (n >= 2).

To verify, consider a few members:

• Ethene (n = 2): C₂H₄ = C₂H₂₍₂₎
• Propene (n = 3): C₃H₆ = C₃H₂₍₃₎
• Butene (n = 4): C₄H₈ = C₄H₂₍₄₎

Each formula fits \(\text{C}_n\text{H}_{2n}\).

The other general formulae belong to different homologous series: \(\text{C}_n\text{H}_{2n+2}\) represents alkanes (saturated hydrocarbons), \(\text{C}_n\text{H}_{2n-2}\) represents alkynes (with a triple bond), and \(\text{C}_n\text{H}_{2n+1}\text{OH}\) represents alkanols (alcohols).