Ethene is an alkene with the molecular formula C2H4. It is a colorless gas with a low boiling point and melting point. As an unsaturated hydrocarbon, ethene is more reactive than saturated hydrocarbons like ethane. It undergoes addition reactions where atoms or groups are added across the double bond, such as halogenation reactions with chlorine and bromine. Ethene also polymerizes through an addition reaction to form the polymer polyethene. It oxidizes when reacted with potassium manganate and combusts to form carbon dioxide and water.