Nomenclature
CAS number: 7782-50-5
Description and references
Cl; at. wt 35.4527; at. no. 17; valences 1,
3, 5, 7. A halogen; Group VIIA (17). Does not exist as elemental
state, Cl, in nature. Occurs as diatomic molecule, Cl2. Abundance in igneous rock (95% of earth's crust): 0.031% by wt;
in seawater: 1.9% by wt (primarily as NaCl). Naturally occurring
stable isotopes (mass numbers): 35 (75.77%), 37 (24.23%); known artificial
radioactive isotopes: 31-34, 36 (longest-lived known isotope, T 1/2 3.0 × 105 yrs; β-, EC decay), 38-46,
48. Discovered in 1774 by C. W. Scheele; recognized as an element
in 1810 by H. Davy. Commercial sources: seawater, ocean derived
mineral deposits, brines from lakes, wells and springs. Industrial
prepn from brine in electrolytic cells. Lab prepn from MnO2 and HCl: Schmeisser in Handbook of Preparative
Inorganic Chemistry vol. 1, G. Brauer, Ed.
(Academic Press, New York, 2nd ed., 1963) p 272. Cosmogenic production
and determn of 36Cl for geological dating: H. E. Gove, Philos. Trans. R. Soc. London Ser. A 323, 103 (1987); M. G. Zreda et al., Earth Planet. Sci. Lett. 105,
94 (1991). Reviews: Ciba Review vol. 12, no. 139 (Aug. 1960); ACS Monograph Series no. 154, entitled “Chlorine,”
J. S. Sconce, Ed. (Reinhold, New York, 1962) 901 pp; MTP Int. Rev. Sci.: Inorg. Chem., Ser. One vol. 3, V. Gutmann, Ed. (Butterworths, London, 1972);
A. J. Downs, C. J. Adams, “Chlorine, Bromine, Iodine and Astatine”
in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr. et al., Eds. (Pergamon
Press, Oxford, 1973) pp 1107-1594; Chemistry
of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon
Press, New York, 1984) pp 920-1041; L. C. Curlin, T. V. Bommaraju
in Kirk-Othmer Encyclopedia of Chemical Technology vol. 1 (Wiley-Interscience, New York, 4th ed., 1994)
pp 938-1025. Review of potential human health and environmental adverse
effects of chlorine and its compounds: E. Delzell et al., Regul. Toxicol. Pharmacol. 2, S1-S1056 (1994).
Properties
Greenish-yellow, diatomic gas; suffocating odor.
mp -101.00°. bp -34.05°. d20 at 6.864 atm 1.4085 (liq); d-35 at 0.9949 atm 1.5649 (liq). d (relative to air) 2.48. Heat capacity at constant pressure
(gas, 25°) 8.11 cal/mole/°C. Vapor pressure data: Giauque, Powell, J. Am. Chem. Soc. 61, 1970 (1939).
Critical temp 144°; critical pressure 76.1 atm; critical density
0.573. Poisonous, corrosive.
Sol in water (25°) with formation of aqueous Cl2 (0.062
moles/l), HOCl (0.030 moles/l) and Cl- (0.030 moles/l);
total soly: 0.092 moles/l. More sol in alkalies. Oxidizing agent.
Very reactive; E0 (aq) 1/2 Cl2/Cl- 1.356
V; dissociation energy (25°): 57.978 kcal. Forms halides with all
elements except the rare gases helium, neon and argon. Noncombustible
in air; most combustible materials will burn in chlorine. Forms explosive
mixtures with flammable gases and vapors. Reacts explosively or forms
explosive compounds with many common chemicals, especially acetylene,
turpentine, ether, ammonia gas, fuel gas, hydrocarbons, hydrogen and
finely divided metals. LC50 (1 hr) in
rats, mice (ppm): 293, 137 (K. C. Back et al., Reclassification of Materials Listed as
Transportation Health Hazards (TSA-20-72-3; PB 214-270,
1972) pp A-182-183).Caution
Potential symptoms of overexposure
are burning of eyes, nose and mouth; lacrimation, rhinorrhea; coughing,
choking and substernal pain; nausea, vomiting; headache, dizziness;
syncope; pulmonary edema; pneumonia; hypoxemia; dermatitis; direct
contact with liquid may cause frostbite. See NIOSH Pocket Guide to Chemical Hazards (DHHS/NIOSH
97-140, 1997) p 58. See also Patty's
Industrial Hygiene and Toxicology vol. 2F,
G. D. Clayton, F. E. Clayton, Eds. (Wiley-Interscience, New York,
4th ed., 1994) pp 4483-4505.Use
Manuf of organic and inorganic chemicals. As oxidizing
and bleaching agent in pulp and paper industry, and for textiles.
As disinfectant for water purification, industrial waste, sewage,
swimming pools. In the extraction and refining of metals.
36Cl for determining geological age of natural samples such as meteorites,
surface rocks, polar ice and ground water. Has been used as a military
poison gas under the name
bertholite.