The chemical formula for carbon monoxide is CO: one carbon atom bonded to one oxygen atom. The formula’s two symbols also explain its name, with “mono-” indicating a single oxygen atom.
Carbon monoxide is a colorless, odorless, tasteless, poisonous, and flammable gas. It commonly forms when carbon-containing fuel burns with too little oxygen for complete combustion. Engines, furnaces, stoves, fireplaces, and generators can all produce it, especially in poorly ventilated spaces.
CO is often confused with carbon dioxide, whose formula is CO₂ and whose molecule contains two oxygen atoms. Carbon monoxide’s carbon–oxygen atoms are connected by a very strong triple bond, and the molecule has a molar mass of about 28.0 grams per mole, making it slightly less dense than average air. In the atmosphere, CO is eventually oxidized to carbon dioxide and typically remains for about one to two months.