PTL:Chlorine
From ChemEd Collaborative
Chlorine is a nonmetal in the 3rd period of Group VIIA, the halogens. Other members of the group are fluorine (F), bromine (Br), iodine (I), and astatine (At). The elemental form consists of diatomic Cl2 molecules.
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Discovered
It was first isolated in 1774 by Scheele, who referred to it as "dephlogisticated marine air". Chlorine was not recognized as an element until 1810, when Davy announced its elementary nature in a memoir to the Royal Society.
Name
The name is derived from the Greek word, chloros, for greenish-yellow, the color of this gaseous element. The symbol Cl is an abbreviation of the name.
Characteristics
At ordinary temperatures chlorine (Cl2) it is a greenish-yellow poisonous gas with a disagreeable, suffocating odor, approximately two and one half times heavier than air.
Found
In nature it is found in the combined state only, chiefly with sodium as common salt (NaCl), in carnallite [KMgCl3·6(H2O)], and in sylvite (KCl). It is a member of the halogen (salt forming) group of elements and is obtained from chlorides by the action of oxidizing agents and more often by electrolysis.
Reactions
Chlorine is an excellent oxidizing agent,
Cl2(g) + 2e- 
2 Cl-(aq) E° = +1.358 V
and that is the basis of much of its chemistry. (It dissolves in water to a small extent and can oxidize water to O2 and HCl.) When dissolved in aqueous base, Cl2 disproportionates to give Cl- (oxidation number = -1) and OCl- (where the Cl oxidation number is +1.)
Cl2(g) + 2 OH- Cl-(aq) + OCl-(aq) + H2O
Uses
Chlorine is widely used in making many everyday products. Most of the chlorine produced is used in the manufacture of chlorinated compounds for sanitation, pulp [bleaching], disinfectants, and textile processing. Further use is in the manufacture of chlorates, chloroform, carbon tetrachloride and in the extraction of bromine. It is also used in preparing some synthetic rubbers and in [petroleum] refining. Finally, it is used to prepare pure hydrochloric acid.
In addition, chlorine is used for producing safe drinking water the world over. Even the smallest water supplies are now usually chlorinated.
Chlorine is a respiratory irritant, and the liquid burns the skin. As little as 3.5 ppm. can be detected as an odor, and 1000 ppm is likely to be fatal after a few deep breaths. It was used as a war gas in World War I.
Emission Spectra
This is the emission spectra for Chlorine.
