klorin

Chlorine, chemical element with symbol Cl and atomic number 17, is a halogen. At room temperature it exists as a diatomic gas (Cl2) that is pale yellow-green and has a sharp, acrid odor. It is a strong oxidizer, highly reactive, and toxic.

Chlorine does not occur free in nature due to its reactivity; it is mainly found in chloride minerals and as chloride ions in seawater and rocks. The largest natural reservoirs are bound in salts such as sodium chloride.

Industrial production is dominated by the chlor-alkali process, which involves the electrolysis of concentrated brine to yield chlorine gas at the anode, with sodium hydroxide and hydrogen formed at the cathode. In the environment, chlorine quickly reacts with organic and inorganic matter, forming a wide range of compounds.

In chemistry, chlorine forms many compounds in which it can exhibit oxidation states from −1 to +7; in elemental form it is 0. When dissolved in water, chlorine forms hypochlorous and hydrochloric acids, giving a mixture that is used for disinfection and bleaching.

Major applications include the production of polyvinyl chloride (PVC) and other organochlorine compounds, water disinfection in drinking water and swimming pools, and household bleaching agents such as sodium hypochlorite. Chlorine also participates in the manufacture of solvents, pharmaceuticals, and agrochemicals.

History notes that Scheele described chlorine’s properties in 1774, and Davy identified it as an element in 1810, naming it chlorine from the Greek chloros, meaning greenish-yellow.

Safety and environmental considerations are significant: chlorine gas irritates the eyes, throat, and lungs and can be fatal at high concentrations. Proper handling, storage, and containment are required to prevent exposure and environmental release, including the formation of toxic chlorinated compounds.