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

Alkanes: properties & bonding

What is an alkane?

• Alkanes are saturated hydrocarbons

  • This means that all carbon-carbon bonds are single bonds (C-C)

• The bonding in alkanes is single covalent

  • 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 alkanes

Properties of alkanes

• Alkanes are colourless compounds

• They are part of the same homologous series

  • So, they show a gradual change in physical properties as the number of carbon atoms in the chain increases

• Alkanes are generally unreactive compounds

  • This is because they contain only strong single covalent bonds

Combustion of alkanes

• Alkanes undergo combustion

• During combustion, alkanes react with oxygen

• Complete combustion produces 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)