Ethylene (C₂H₄) — Properties, Uses & Safety

Overview

Ethylene (C2H4), also known as ethene, is the simplest alkene and the most produced organic chemical in the world, with global production exceeding 200 million tons per year. With a molar mass of 28.05 g/mol, ethylene is a colorless, flammable gas with a faint sweet odor at standard temperature and pressure. Its molecular structure features a carbon-carbon double bond, making it the foundational example for teaching about alkenes, pi bonds, and sp2 hybridization in organic chemistry. The two carbon atoms and four hydrogen atoms in ethylene all lie in the same plane, with H-C-H bond angles of approximately 117°, close to the ideal 120° for trigonal planar geometry. The C=C double bond consists of one sigma bond and one pi bond, and the restricted rotation around this double bond is what gives rise to geometric (cis-trans) isomerism in substituted alkenes. Ethylene is produced industrially by steam cracking of hydrocarbons (ethane, naphtha, or gas oil) at temperatures above 800 °C. It serves as the starting material for an enormous range of chemical products. The most important use is the production of polyethylene — the world's most common plastic — through addition polymerization. Other major derivatives include ethylene oxide (for ethylene glycol/antifreeze), styrene (for polystyrene), vinyl chloride (for PVC), and acetaldehyde. In nature, ethylene plays a remarkable role as a plant hormone. It regulates fruit ripening, flower wilting, leaf abscission, and seed germination. This is why placing an unripe banana next to ripe fruit speeds up ripening — the ripe fruit releases ethylene gas. Commercial fruit distributors use ethylene gas to ripen bananas, tomatoes, and other produce on demand. Safety considerations include extreme flammability and the risk of forming explosive mixtures with air. GHS pictograms include the flame and gas cylinder symbols. For chemistry students, ethylene is essential for understanding double bonds and pi bonding, addition reactions (hydrogenation, halogenation, hydration, polymerization), Markovnikov's rule, sp2 hybridization and molecular geometry, and the industrial importance of petrochemistry. The polymerization of ethylene to polyethylene is one of the most impactful chemical reactions in modern civilization.

IUPAC Name

ethene

CAS Number

74-85-1

PubChem CID

6325

Molecular Formula

C₂H₄

Molar Mass

28.054 g/mol

State at STP

gas

Appearance

Colorless, flammable gas