ClCl

ClCl is the notation sometimes used to represent the diatomic chlorine molecule, Cl2, in plain text or in SMILES (Simplified Molecular Input Line Entry Specification). It is not a separate chemical species; the conventional formula is Cl2, and its systematic name is dichlorine.

At room temperature, chlorine exists as a pale greenish-yellow gas with a strong, acrid odor. It has a boiling point of -34.04 °C and a melting point of -101.5 °C. As a dense gas, its approximate density is 3.2 g/L at standard conditions. Chlorine is a highly reactive oxidizing agent that participates in many chemical reactions, often forming salts or oxides with various elements.

Industrial production occurs chiefly through the electrolysis of sodium chloride solutions or fused NaCl, in the chlor-alkali process, yielding chlorine gas and sodium hydroxide. In nature, free chlorine gas is not stable for long and is present in trace amounts in the atmosphere under certain conditions.

In aqueous environments, chlorine reacts with water to form hypochlorous acid and hydrochloric acid: Cl2 + H2O ⇌ HOCl + HCl. This chemistry underpins its use as a disinfectant and bleaching agent. In organic synthesis, Cl2 adds to alkenes to produce vicinal dichlorides and participates in various chlorination and oxidation reactions. Chlorine gas is also the active ingredient in many bleaching powders and water-treatment applications.

Safety considerations are paramount: chlorine gas is highly toxic and corrosive, causing respiratory and eye irritation and potentially life-threatening damage at high concentrations. It is stored and handled under strict containment with adequate ventilation and appropriate protective equipment.