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| Name | Chlorine |
| Atomic number | 17 |
| Category | Halogen |
| Appearance | Pale greenish-yellow gas |
| Atomic mass | 35.45 |
| Phase | Gas at STP |
| Melting point | −101 °C |
| Boiling point | −34 °C |
| Electronegativity | 3.16 (Pauling) |
cl
The element chlorine is a halogen chemical element with symbol Cl and atomic number 17, known for its high reactivity and wide industrial use. Chlorine appears in many historical, industrial, and scientific contexts from early chemical nomenclature to modern water treatment, and it features prominently in studies involving Dmitri Mendeleev, Antoine Lavoisier, Carl Wilhelm Scheele, Sir Humphry Davy, and the development of the Periodic Table. Its chemistry connects to industries and institutions such as Dow Chemical Company, Basf SE, DuPont, Union Carbide, and to environmental and regulatory bodies like the United States Environmental Protection Agency, European Chemicals Agency, and World Health Organization.
Etymology and usage
The name derives from the Greek roots used by early chemists and was formalized during the late 18th and early 19th centuries by figures including Antoine Lavoisier, Carl Wilhelm Scheele, and Sir Humphry Davy. Chlorine’s nomenclature entered international chemical vocabularies through codification in works associated with the IUPAC and textbooks by authors such as Dmitri Mendeleev and later editions endorsed by organizations like Royal Society of Chemistry and academic publishers including Elsevier and Springer. Historical usage spans from bleaching innovations in the era of Industrial Revolution textile centers in Manchester and Rouen to modern standards set by bodies like the American Chemical Society.
Chemical properties
Chlorine is a diatomic gas at standard conditions, exhibiting strong oxidizing behavior and forming compounds across many oxidation states when combined with elements such as Sodium, Potassium, Carbon, Hydrogen, Iron, and Silicon. Its high electronegativity and electron affinity underpin reactions catalogued in the seminal works of Linus Pauling and in modern inorganic texts used at institutions like Massachusetts Institute of Technology and University of Cambridge. Chlorine forms stable halides such as with Sodium chloride, reactive species including chlorine dioxide, and covalent chlorinated organics studied in research from laboratories at Lawrence Berkeley National Laboratory and Max Planck Institute for Chemistry.
Occurrence and production
Chlorine occurs naturally in seawater, mineral deposits like halite and in evaporite formations exploited by mining companies operating in regions such as Dead Sea basins and the Great Salt Lake. Industrial production historically shifted with technologies developed by firms including Solvay Company and modern electrochemical processes deployed by Ineos and others using electrolytic cells derived from innovations at Bell Labs and industrial research centers. Large-scale production sites are located near chemical hubs such as Gulf Coast, United States, Ruhr, and Ningbo, China, and logistics involve trade governed by frameworks like the World Trade Organization.
Applications and compounds
Chlorine is central to the manufacture of polymers such as polyvinyl chloride at facilities run by corporations like Formosa Plastics Group and Shin-Etsu Chemical Co., and to synthesis of solvents, intermediates, and pesticides historically developed by companies including Monsanto and Bayer. It is critical in water disinfection practices adopted by municipalities guided by standards from the World Health Organization and Centers for Disease Control and Prevention, and it features in household products and industrial reagents referenced in catalogs of firms like Fisher Scientific and Sigma-Aldrich. Chlorinated compounds range from inorganic salts such as sodium chloride to organic compounds like trichloroethylene, DDT, polychlorinated biphenyls, and pharmaceuticals whose development and regulation involved entities like Food and Drug Administration and European Medicines Agency.
Isotopes and nuclear properties
Chlorine has two stable isotopes, 35Cl and 37Cl, with applications in isotope geochemistry and tracer studies performed at institutions such as Lawrence Livermore National Laboratory and Scripps Institution of Oceanography. Radioisotopes like 36Cl have been used in studies of cosmic-ray exposure, hydrogeology, and radiometric dating by researchers affiliated with Oak Ridge National Laboratory and the United States Geological Survey. Nuclear data for chlorine isotopes are compiled in databases maintained by organizations including the International Atomic Energy Agency and incorporated into experimental programs at facilities such as CERN and national accelerator centers.
Biological and environmental effects
Chlorine and many chlorinated compounds have significant impacts on human health and ecosystems, prompting regulatory action by agencies including the Environmental Protection Agency, European Chemicals Agency, and global monitoring by the United Nations Environment Programme. Chlorine-based disinfection reduces waterborne disease pressures documented by the World Health Organization and Centers for Disease Control and Prevention but chlorinated organic byproducts are scrutinized in studies from universities such as Harvard University and Johns Hopkins University for links to health outcomes. Environmental incidents involving chlorinated releases have triggered responses coordinated by organizations like Red Cross and governmental responders including Federal Emergency Management Agency and influenced international agreements comparable to protocols discussed in forums like the Stockholm Convention.