Compounds containing only single carbon–carbon bonds are described as saturated.

Compounds containing at least one carbon–carbon double bond are described as unsaturated.

Compounds containing carbon–carbon double bonds can take part in addition reactions.

In an addition reaction, two molecules combine to form a single molecule.

Unsaturated compounds can be distinguished from saturated compounds using bromine solution, as unsaturated compounds quickly decolourise bromine solution.

Isomers

• are compounds with the same molecular formula but different structural formulae

• may belong to different homologous series

• usually have different physical properties

  → even/especially if they belong to the same homologous series

The solubility, boiling point and volatility (ease of evaporation) of a compound are affected by the following factors:

• the presence of $O-H$ or $N-H$ bonds, which implies hydrogen bonding
• the spatial arrangement of polar covalent bonds which could result in a molecule possessing a permanent dipole
• molecular size which would affect London dispersion forces
• the polarities of solute and solvent

→ boiling points increase with increased strength of intermolecular forces

→ compounds are more volatile the weaker intermolecular forces are