Chlorine

Chlorine (symbol Cl) is a chemical element with atomic number 17. It belongs to the halogen group on the periodic table, a group of elements that react readily with other elements. In its ordinary state, chlorine is a pale greenish-yellow gas with a strong smell.

Chlorine does not occur naturally in free form in the atmosphere because it reacts readily with other substances. It is found mostly in compound form, particularly as sodium chloride (NaCl), which is table salt and sea salt. For this reason, seawater and underground salt deposits are the main sources from which it is extracted.

Chemical properties

Chlorine is a strong oxidizer, meaning it removes electrons from other elements. It reacts readily with most metals and many non-metals, producing compounds called chlorides. When chlorine gas is mixed with water, it forms a mixture of hydrochloric acid and hypochlorous acid, which gives it strong disinfectant properties.

Production

The most common industrial method is electrolysis of a salt solution (brine). When electric current is passed through the solution, chlorine is released at the anode, while hydrogen and sodium hydroxide (caustic soda) are produced at the cathode. This process is known as chlor-alkali manufacturing and simultaneously produces three commercial products.

Uses

The main use is the disinfection of drinking water and swimming pools, killing bacteria and other microorganisms. It is also used in the manufacture of various products including PVC, pharmaceuticals, pesticides, and many industrial chemicals. It is used domestically in bleach, which is based on sodium hypochlorite.

Health hazards

Inhalation of chlorine gas at high levels can damage the lungs and respiratory passages. Chlorine has been documented as a chemical weapon used during the First World War. Today, international chemical weapons treaties regulate its use in warfare, while industrial uses are subject to strict safety regulations.