Physical Properties of Alkanes

Physical Properties of Alkanes

  1. Alkanes are covalent compounds, hence their physical properties are similar to other covalent compounds.
  2. The atoms in an alkane molecule are bonded together by strong covalent bonds  (intramolecular forces).
  3. The molecules are held together by weak Van der Waals forces (intermolecular forces).

Boiling Points

Boiling Point of Alkane
  1. The boiling point of alkane increase when the number of carbons in the molecule increases.
  2. This is due to the increase of Van der Waal force when the size of the molecule increases.
  3. The boiling points shown are all for the “straight chain” isomers when there are more than one.
  4. The first four alkanes are gas at room temperature.
  1. Alkanes are insoluble in water, but dissolve in organic solvents.
  2. The liquid alkanes are good solvents for many other covalent compounds.


  1. The density of water is higher than density of most alkanes.
  2. When going down the series, relative molecular mass of alkanes is higher due to the higher force of attraction between molecules and alkane molecules are packed closer together.

Electrical Conductivity

  1. All members in alkanes do not conduct electricity.
  2. Alkanes are covalent compounds and do not contain freely moving ions.

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