Cl2

Cl2, or chlorine gas, is the diatomic molecule consisting of two chlorine atoms. It is a greenish-yellow gas at room temperature with a sharp, pungent odor and is denser than air. In water it dissolves only to a limited extent but reacts with water to form hypochlorous acid (HOCl) and hydrochloric acid (HCl), making aqueous chlorine solutions moderately active oxidizing and disinfecting agents.

Industrial production and handling are dominated by the chlor-alkali process, in which concentrated sodium chloride brine is electrolyzed to yield chlorine gas, sodium hydroxide, and hydrogen. Lab-scale chlorine is often generated on demand by the reaction of hydrochloric acid with oxidizing agents. Because of its strong oxidizing properties, Cl2 is highly reactive and can form a wide range of chlorinated compounds.

Uses are broad and include disinfection of drinking water and swimming pools, bleaching of textiles and paper, and the synthesis of numerous organochlorine compounds. It is a key reagent in the production of polyvinyl chloride (PVC) and various solvents and agrochemicals. In chemical manufacturing, chlorine gas is employed to chlorinate hydrocarbons and to oxidize substrates.

Safety and environmental considerations are significant. Cl2 is toxic and corrosive; exposure can irritate the eyes, skin, and respiratory tract and can cause severe pulmonary effects at high concentrations. It reacts with moisture and organic materials, and improper handling can lead to dangerous fires or explosions in the presence of some reductants. Environmentally, chlorine species can participate in atmospheric reactions that affect ozone, and chlorinated organics can persist in ecosystems if released.

Storage and containment require corrosion-resistant equipment, appropriate ventilation, and measures to prevent release and unintended reactions.