C2H4

C2H4, commonly called ethene or ethylene, is the simplest alkene and one of the most important organic chemicals. It consists of two carbon atoms linked by a double bond and four attached hydrogen atoms. The C=C bond is composed of one sigma and one pi bond; each carbon is sp2-hybridized, resulting in a molecule that is planar around the double bond.

Ethylene is a colorless, flammable gas at room temperature and pressure. It has a boiling point of −103.7 °C and a melting point of −169.2 °C. It is typically stored under pressure as a liquid in low-temperature containment and is commonly handled as a compressed gas. It has no odor unless an odorant is added.

Ethylene is mainly produced by steam cracking of hydrocarbons such as ethane, propane, or naphtha, followed by purification and distillation. It is a key feedstock in petrochemical industries. Small-scale production can occur by dehydration of ethanol or other routes, but industrially steam cracking is dominant.

The C=C bond makes ethylene highly reactive toward additions (halogens, hydrogen halides, water, etc.). It polymerizes readily to polyethylene, which is the foundation of most plastics. It is also used to manufacture ethylene oxide (a precursor to ethylene glycol), and other chemicals such as ethylbenzene and vinyl acetate via downstream processes.

Ethylene is highly flammable and forms explosive mixtures with air at sufficient concentrations. It is stored and transported as a liquefied gas and requires appropriate containment and leak detection. As a volatile organic compound, it participates in atmospheric chemistry and is subject to regulatory controls in many jurisdictions.