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Properties of alkanes needed for IGCSE

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  • Alkanes are saturated hydrocarbons. They have a general formula and the straight chain alkanes have a name which depends on the number of carbons in the chain. Their structural or formula shows all the bonds in a molecule.
  • The physical properties (such as boiling point) of alkanes show a gradual trend or change as the carbon chain length increases and this could be shown in a graph. There are many examples of physical properties and many of these depend on the mass of the molecules which affects the size of the intermolecular forces between molecules
  • Alkanes can exist as isomers.  These are molecules with the same molecular formula but different structural formulae. Butane has one isomer and pentane has two isomers. Isomers have the same chemical properties but their physical properties may differ slightly as their different shapes lead to differences in the size of the intermolecular forces.
  • Alkanes are good fuels and undergo combustion reactions.  The products of these reactions depends on the amount of oxygen available.  Complete combustion in excess oxygen produces carbon dioxide and water, however incomplete combustion in limited oxygen can produce carbon monoxide and water or carbon and water.  
  • Carbon monoxide is poisonous or toxic because it binds to the haemoglobin in red blood cells and prevents these cells from carrying oxygen.  This can be fatal.  Carbon is a respiratory irritant.
  • Alkanes undergo substitution reactions with halogens in the presence of UV light. The products are halogenoalkanes and the hydrogen halide.  For example methane and bromine will form bromomethane and hydrogen bromide.
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