* Chlorine is a member of the halogen family:
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CHLORINE / Cl / 17
Elemental chlorine is found in nature as Cl2 gas, which has a
sickly-yellow color, is highly reactive, and highly toxic.
Two isotopes are found in nature:
Cl<35/17> / 76%
Cl<37/17> / 24%
Both are stable. The radioactive chlorine isotope Cl<36/17>, with
a half-life of 300,000 years, is used in research applications.
atomic weight: 35.4527
abundance: 20th
density: 3.2 gm/l
melting point: -101 C
boiling point: -35 C
valence: 1 3 5 7
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The "Cl-" ion is known as "chloride", while the "ClO3-" group is known as "chlorate". Chlorine is a very important industrial chemical, being mostly derived from sodium chloride (NaCl / table salt) deposits and with production well over a hundred million tonnes a year. It is used as a bleaching agent, solvent, and constituent of plastics. NaCl is also a critical component of the human diet, though too much table salt is hazardous to the health as well. During the First World War, chlorine gas was used as a weapon, an asphyxiating agent, but it was quickly replaced by more effective gases.
Chlorine is added to water supplies to kill pathogens. As with fluoridation of water supplies, there have been concerns about water chlorination, though the data supporting its effectiveness has been solid enough to overcome serious opposition. There is still an interest in purifying water supplies with less troublesome chemicals; ozone -- the reactive O3 molecule -- is also used for this purpose to a limited extent.
