A halogen element; a.n. 17; r.a.m. 35.453; d. 3.214 g dm−3; m.p. –100.98°C; b.p. –34.6°C. It is a poisonous greenish-yellow gas and occurs widely in nature as sodium chloride in seawater and as halite (NaCl), carnallite (KCl.MgCl2.6H2O), and sylvite (KCl). It is manufactured by the electrolysis of brine and also obtained in the Downs process for making sodium. It has many applications, including the chlorination of drinking water, bleaching, and the manufacture of a large number of organic chemicals.
It reacts directly with many elements and compounds and is a strong oxidizing agent. Chlorine compounds contain the element in the 1, 3, 5, and 7 oxidation states. It was discovered by Karl Scheele in 1774 and Sir Humphry Davy confirmed it as an element in 1810.
https://www.webelements.com/chlorine/ Information from the WebElements site