Clionen

ClIonen, written as chloride ions (Cl−), are the negatively charged counterparts of chlorine atoms. In aqueous solutions and many minerals they form salts with various cations, and they play a central role in chemistry, biology, and industry. Chloride ions are typically represented simply as Cl− in chemical formulas and reaction equations.

Chloride ions are ubiquitous in nature. They are a major component of seawater and are found in large quantities in minerals such as halite (NaCl). Industrially, chloride ions are present in brines and can be released during processes that involve sodium chloride, such as the electrochemical production of chlorine gas, where Cl− remains in solution and supports electrical conductivity. In many biological and environmental contexts, chloride is often considered an essential electrolyte.

In chemistry, Cl− is a relatively weak reducing agent and is the conjugate base of the strong acid hydrochloric acid (HCl). It participates in redox processes only under specific conditions, and it forms a wide variety of salts with metal and nonmetal cations. In biology, chloride ions are important for maintaining osmotic pressure and electrical neutrality in body fluids. They are involved in the chloride shift that enables carbon dioxide transport in red blood cells and are essential for stomach acid production via hydrochloric acid.

Chloride ions have numerous uses. They are part of table salt (NaCl), widely used in food flavoring and preservation, de-icing, and water treatment. Industrially, chloride-containing compounds are precursors to polymers such as PVC and to various organochlorine chemicals. While typical dietary levels are safe and necessary, high concentrations of chloride salts can be harmful and environmental exposure to concentrated chlorine-containing species can pose risks.