Chlorine is added to swimming pools to kill off potentially dangerous bacteria. This is achieved thanks to a chemical reaction between chlorine's hypochlorous acid and hypochlorite ions and the cell walls of the bacteria. Chlorine's chemicals penetrate the cells and attack their enzymes, which oxidizes the bacteria, making them harmless. The hypochlorous acid works in just a few seconds, but the hypochlorite ion requires up to 30 minutes. Once the chlorine has done its job, it either mixes with another chemical or breaks down into individual atoms. Either way, it becomes harmless. More chlorine has to be added regularly to keep the pool bacteria-free.
Chlorine is a busy element, with a lot of work listed on its resume. The green-yellow gas, a proud member of the halogen group on the Periodic Table of Elements, is used to keep drinking water safe and finds other uses in areas as varied as medicines, textiles and insecticides. And, of course, it's used to bring about sodium chloride, otherwise known to food lovers everywhere as table salt. Organic chemists also use chlorine in substitution reactions and to promote oxidation [source: Royal Society of Chemistry].
The element was discovered way back in 1774 by a Swedish man named Carl Wilhelm Scheele, although he did not recognize it as an element (that designation did not come until years later). Chlorine gas can irritate the respiratory system at low concentration levels and it can even be fatal at higher exposure levels. At basic levels it will smell like bleach [source: The Chlorine Institute].
Chlorine was identified as an element by Sir Humphry Davy in 1810 and he gave it the name chlorine after the Greek word chloros, which means yellowish-green, in reference to the new element's color [source: Woodrow Wilson National Fellowship Foundation].
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