Chlorine is a nonmetallic element, with element symbol Cl and atomic number 17, which is located in the third period and belongs to group VII A, and is one of the halogen elements. Chlorine is composed of two chlorine atoms, and the chemical formula is Cl2.

Gaseous chlorine is called chlorine and liquid chlorine is called liquid chlorine. Chlorine gas is yellow-green gas at normal temperature and pressure, with strong pungent smell, very active chemical properties and toxicity. Chlorine exists widely in nature in the form of combined state, which is also of great significance to human physiological activities.

1774, Swedish chemist Scheler found that pyrolusite mixed with hydrochloric acid would generate a suffocating yellow-green gas when heated.

At that time, the great chemist lavoisier thought that oxygen was the origin of acidity, and all acids contained oxygen. Scheler and many chemists firmly believe lavoisier's view that this yellow-green gas is a compound composed of oxygen and another unknown radical, so Scheler calls it "hydrochloric acid oxide".

But David, a British chemist, holds a different view. He tried his best to extract oxygen from hydrochloric acid oxide and failed. He suspected that there was no oxygen in hydrochloric acid oxide at all.

18 10, David proved with irrefutable facts that the so-called hydrochloric acid oxide is not a compound, but a simple substance of a chemical element. He named this element "Chlorine". Its original Greek meaning is "green". Chinese translation is chlorine.