Chlorine

Chlorine (IPA: , Greek: χλωρóς chloros, meaning "pale green"), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 7. As the chloride ion, which is part of common salt and other compounds, it is abundant in nature and necessary to most forms of life, including humans. In its elemental form under standard conditions, it is a pale green gas about 2.5 times as dense as air. It has a disagreeable, suffocating odor that is detectable in concentrations as low as 3.5 ppm and is poisonous. Chlorine is a powerful oxidant and is used in bleaching and disinfectants. As a common disinfectant, it is used in swimming pools to keep them clean. In the upper atmosphere, chlorine atoms have been implicated in destruction of the ozone layer.