Atomic Properties of Cl
- Atomic Number of Cl
- 17
- Atomic Mass of Cl
- 35.4500 u
- Electron Configuration
- [Ne] 3s2 3p5
- Electronegativity
- 3.16
- Block
- p-block
- Group
- 17
- Period
- 3
Chlorine presents one of chemistry's sharpest context changes. Elemental Cl2 is a poisonous greenish-yellow gas that attacks moist tissues and must be contained carefully. Chloride ions, by contrast, are stable components of seawater, table salt, and the fluids inside the human body. Gaining one electron changes a hazardous element into a familiar ion.
Water treatment uses another controlled transformation. When chlorine or chlorine-releasing compounds enter water, they form disinfecting species including hypochlorous acid. These oxidize essential parts of many microorganisms, helping prevent waterborne disease. Operators must balance concentration, contact time, acidity, and unwanted by-products. The goal is a measured residual that protects water through distribution, not a pool filled with elemental gas.
Industry begins mostly with brine, a concentrated sodium chloride solution. Electrolysis separates its components to produce chlorine, hydrogen, and sodium hydroxide, three major chemical feedstocks. Chlorine chemistry supports bleaches, hydrochloric acid, medicines, solvents, and polymers such as PVC. Its reach comes from reactivity that can build useful bonds as readily as it can damage tissue.
Carl Wilhelm Scheele produced chlorine in 1774 but interpreted it through the chemistry of his era. Humphry Davy argued in 1810 that it was an element and named it for its green color.
Chlorine is the Collection Agent whose reputation cannot be summarized as safe or dangerous. Cl2 gas, chloride in salt, and hypochlorous acid in treated water have different structures and behavior. Good chemistry identifies the species, concentration, and setting before judging the name on the label.