Chlorine
halogenProperties
| Property | Value |
|---|---|
| Atomic Mass | 35.45 amu |
| Category | halogen |
| Group | 17 |
| Period | 3 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p5 |
| Electronegativity | 3.16 (Pauling) |
| Oxidation States | 7, 5, 3, 1, -1 |
| Melting Point | 171.6 K (-101.5 °C) |
| Boiling Point | 239.11 K (-34.0 °C) |
| Density | 0.003214 g/cm³ |
| Discovered By | Carl Wilhelm Scheele (1774) |
About Chlorine
Chlorine sits one electron short of an argon shell, and that single missing electron drives almost everything interesting about it. The Cl-Cl bond is weak enough (about 243 kJ/mol) that UV light cracks it into radicals, which is why chlorine chemistry is the textbook example for free-radical halogenation in undergraduate organic. Pulled out of brine via the chlor-alkali process, it leaves the cell hot, wet, and contaminated with oxygen, so plants run it through sulfuric-acid drying towers before liquefying it under pressure. As an electrophilic chlorinating agent it builds PVC, vinyl chloride, and roughly half the molecules a working pharmaceutical chemist sees in a typical week. The hypochlorite ion (ClO⁻) you generate by bubbling Cl₂ into cold NaOH is the active species in household bleach, and a tenth of a milligram per liter of free chlorine is enough to keep municipal water free of coliforms. The reagent is unforgiving — even a small leak in a lecture-bottle regulator clears a lab in seconds.
Fun Fact
Jersey City started chlorinating its water supply in 1908 — about 0.2 ppm free chlorine — and typhoid mortality there dropped roughly 90% inside a decade. Most of the public-health gains attributed to 'modern medicine' in the early twentieth century were really chlorine and copper pipe.
Common Uses
- Water purification and disinfection of drinking water
- PVC (polyvinyl chloride) plastic production
- Bleach (sodium hypochlorite) for cleaning and disinfection
- Production of hydrochloric acid for industry
- Manufacturing of pesticides, pharmaceuticals, and solvents