chlór

Chlór, known in English as chlorine, is a chemical element with the symbol Cl and atomic number 17. It is a member of the halogen group and exists mainly as a diatomic molecule, Cl2, at room temperature. Chlorine gas is a greenish-yellow, highly reactive substance with a sharp odor. It has a melting point of −101.5 °C and a boiling point of −34.04 °C. As a strong oxidizer, chlorine forms a wide range of chlorides.

Occurrence and production: Chlorine does not occur freely in nature due to its reactivity; it is found primarily as chloride salts in seawater, brines, and sedimentary rocks. Industrial production is dominated by the chlor-alkali process, which electrochemically converts sodium chloride solution into chlorine gas and sodium hydroxide. The reaction is 2 NaCl → 2 Na + Cl2. Purified chlorine is used to make many organic and inorganic compounds.

Applications: The main uses are water disinfection and pool sanitation, bleaching of paper and textiles, and the manufacture of chlorinated organics such as vinyl chloride (for PVC) and many solvents. It is also employed to produce pesticides, solvents, and various intermediates in chemical syntheses.

Safety and environmental aspects: Chlorine gas is highly toxic and corrosive; exposure can irritate the eyes, skin, and lungs and can be fatal at high concentrations. In water, chlorine forms hydrochloric acid and hypochlorous acid. Environmentally, chlorine-containing compounds can be persistent and may contribute to ozone depletion in the upper atmosphere and to photochemical smog when released in air.

History and name: Discovered by Carl Wilhelm Scheele in 1774; the name chlorine derives from the Greek chloros, meaning greenish-yellow, and was popularized by Humphry Davy.