Cloro

Cloro, or chlorine, is a chemical element with the symbol Cl and atomic number 17. It belongs to the halogen group in period 3. At room temperature it is a greenish‑yellow diatomic gas (Cl2) and is highly reactive; in many compounds it appears as chloride (Cl−). It is one of the most electronegative elements.

In nature, chlorine does not occur free due to its reactivity. It is found mainly as chloride ions in oceans, rocks, and salts. The principal industrial method for producing chlorine gas is the chlor-alkali process, which electrolyzes sodium chloride (table salt) solution to yield Cl2 gas along with sodium hydroxide (NaOH) and hydrogen.

Chlorine has a wide range of applications. It is widely used to disinfect drinking water and swimming pools and to bleach paper and textiles. It is a key feedstock for the production of polyvinyl chloride (PVC) and many other organic chemicals. Chlorine participates in numerous chemical processes, including the synthesis of chlorinated solvents, pesticides, and pharmaceuticals.

Safety and biology are important considerations. Chlorine gas is toxic and a strong irritant to the eyes, skin, and respiratory tract; high concentrations can be life‑threatening. The chloride ion (Cl−) is an essential nutrient in many organisms, supporting fluid balance, digestion, and nerve function.

History notes: chlorine was discovered by Carl Wilhelm Scheele in 1774 as part of muriatic acid, and later recognized as an element by Humphry Davy, who named it from the Greek chloros, meaning greenish‑yellow. Its industrial prominence grew with the chlor-alkali industry and widespread disinfection uses.