Ethene molecule rotating, animation. Ethene, or ethyelene (C2H4), is the simplest alkene, that is, a hydrocarbon containing a carbon-carbon double bond. The double bond makes it very reactive, as it can be broken by numerous processes. Ethene can be polymerised to form polythene (polyethylene, or PE), which is the most common plastic in the world. This is formed of long chains of ethene molecules in which the double bond is broken and attached to the carbons of other ethene molecules (-CH2CH2-). It can also be hydrogenated, where the double bond is broken and attached to two other hydrogen atoms, giving ethane (C2H6). See clips K003/5080 and K003/ for polymerisation and hydrogenation of ethene respectively.