Chlorine was discovered in 1774 by K.W. Scheele, a Swedish chemist; he liberated this element for the first time by heating manganese dioxide with hydrogen chloride, HCl, an acid first made by alchemists in the 15th century and named "muriatic acid" by the French chemist Lavoisier. Scheele thought that the yellow-green product gas was a compound, naming it "oximuriatic acid" because he thought that the gas resulted from the combination of oxygen and "muriatic acid". This erroneous opinion was supported by the work of Berthollet, in 1785, who observed the production of oxygen when the chlorine solution was exposed to light.

Gay-Lussac and Thénard, in 1809, tried to separate its components by exposing the pure dry gas to incandescent carbon. Davy, in 1810, tried again to do this separation, but was obviously unsuccessful, concluding that it was an element, not a compound. Davy named this new element as chlorine, derived from the Greek "khloros" that means greenish-yellow.