Chlorine

A chemical element, in the periodic table Chlorine has the symbol Cl and atom number 17, and is one of the halogens. The pure chemical element has the physical form of a diatomic green gas. The name chlorine is derived from chloros, meaning green, referring to the colour of the gas. There are two principal stable isotopes of chlorine, of mass 35 and 37, found in the relative proportions of 3:1 respectively, giving chlorine atoms in bulk an apparent atomic weight of 35.5.

Chlorine is an important chemical in water purification and in mustard gas.