Alkanes (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Alkanes: properties & bonding

What is an alkane?

• Alkanes are a group of saturated hydrocarbons

• The term saturated means that they only have single carbon-carbon bonds, there are no double bonds

• Alkanes have covalent bonds as they consist of non-metal atoms 

• The general formula of the alkanes is C_nH_2n+2

Table of alkanes

Displayed formula	Name	Molecular formula
	methane	CH4
	ethane	C2H6
	propane	C3H8
	butane	C4H10
	pentane	C5H12

The first five members of the alkane homologous series

• Alkanes are colourless compounds which have a gradual change in their physical properties as the number of carbon atoms in the chain increases

• They are generally unreactive compounds but they:

  • Undergo combustion

  • Can be cracked into smaller molecules

  • React with halogens in the presence of light in substitution reactions

Combustion of alkanes

• Alkanes undergo complete combustion to form carbon dioxide and water:

Alkane + oxygen → carbon dioxide + water

• Combustion of methane:

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (l)

• Combustion of ethane:

C₂H₆ (g) + 3½O₂ (g) → 2CO₂ (g) + 3H₂O (l)

• Combustion of propane:

C₃H₈ (g) + 5O₂ (g) → 3CO₂ (g) + 4H₂O (l)

• Combustion of butane:

C₄H₁₀ (g) + 6½O₂ (g) → 4CO₂ (g) + 5H₂O (l)