It is a chemical element with the atomic number 17. It is represented by the symbol Cl. Chlorine is a member of the halogens group. It can be found in group 17 and the 3rd period of the periodic table. It is a p-block element. Chlorine is a yellow-greenish gas at room temperature. It is extremely reactive and has a high electron affinity. The electronic configuration is [Ne] 3s2 3p5. The standard atomic weight is 35.45. The oxidation state of chlorine is −1, +1, +2, +3, +4, +5, +6, +7 depending on the bonding atom and its electron affinity. It has an electronegativity 3.16 (Pauling scale). Its melting point is 171.6 K ?(−101.5 °C, ?−150.7 °F) and its boiling point is 239.11 K ?(−34.04 °C, ?−29.27 °F).

There are some 25 isotopes of Chlorine in which two are stable isotopes and the remaining are radioisotopes. The two stable isotope Cl-35 and Cl-37 have 76% and 24% respectively. Chlorine was discovered by Carl Wilhelm Scheele in 1774 as a compound, It was later recognized by English chemist Sir Humphry Davy as an element and given the name Chlorine.

Chlorine is very reactive and can be found in the form of chloride salts. It has a large number of applications, as a bleaching agent, used in sanitation, disinfectant and in plastic production. It was also used as a chemical weapon in WWI.