定义Definition
氯是第 17 号元素，符号 Cl，位于第三周期第 17 族，是卤素。单质氯气 Cl₂ 是有刺激性气味的黄绿色有毒气体，氧化性很强。氯在自然界主要以氯化物存在，海水中含大量 NaCl。
Chlorine is element 17, symbol Cl, in period 3 and group 17, a halogen. The element, Cl₂, is a toxic yellow-green gas with a choking smell and a strong oxidising agent. It occurs mainly as chlorides; seawater contains a great deal of NaCl.
元素数据Element data
| 原子序数Atomic number | 17 |
|---|---|
| 元素符号Symbol | Cl |
| 相对原子质量Standard atomic weight | 35.45 |
| 电子排布Electron configuration | [Ne] 3s² 3p⁵ |
| 族 / 周期 / 区Group / period / block | 17 / 3 / p |
| 电负性（鲍林）Electronegativity (Pauling) | 3.16 |
| 常见氧化态Common oxidation states | −1, +1, +3, +5, +7 |
化学性质Chemistry
氯原子得到一个电子形成 Cl⁻，氯气是强氧化剂：与钠、铁等金属剧烈反应生成氯化物（2Fe + 3Cl₂ → 2FeCl₃），能把 Br⁻、I⁻ 氧化为 Br₂、I₂。与水反应生成盐酸和次氯酸：Cl₂ + H₂O ⇌ HCl + HClO；与冷 NaOH 溶液反应生成次氯酸钠（歧化反应）。在紫外光下与烷烃发生自由基取代。
A chlorine atom gains one electron to form Cl⁻, and chlorine gas is a strong oxidiser: it reacts vigorously with metals such as sodium and iron to form chlorides (2Fe + 3Cl₂ → 2FeCl₃) and oxidises Br⁻ and I⁻ to Br₂ and I₂. With water it forms hydrochloric and chloric(I) acids, Cl₂ + H₂O ⇌ HCl + HClO, and with cold NaOH it gives sodium chlorate(I) by disproportionation. In UV light it substitutes alkanes by a radical mechanism.
制备与用途Production and uses
工业上电解饱和食盐水（氯碱工业）同时制得氯气、氢气和氢氧化钠。实验室用浓盐酸与 MnO₂ 加热制取。氯用于自来水消毒、制漂白剂和 PVC 等含氯有机物。
Industrially, electrolysis of brine (the chlor-alkali process) gives chlorine, hydrogen and sodium hydroxide together. In the laboratory it is made by heating concentrated hydrochloric acid with MnO₂. Chlorine disinfects drinking water and is used to make bleach and organochlorine products such as PVC.
安全Safety
氯气密度比空气大，有毒，刺激呼吸道，高浓度可致命。使用时需在通风橱中进行。含次氯酸盐的漂白剂与酸性清洁剂混合会放出氯气，切勿混用。
Chlorine is denser than air and toxic; it attacks the airways and can kill at high concentration. Use it in a fume cupboard. Hypochlorite bleach mixed with acidic cleaners releases chlorine and must never be combined.
化学性质Chemical properties
与水反应：Cl₂ + H₂O ⇌ HCl + HClO
With water: Cl₂ + H₂O ⇌ HCl + HClO
置换溴化物中的溴：Cl₂ + 2KBr → 2KCl + Br₂
Displaces bromine from bromides: Cl₂ + 2KBr → 2KCl + Br₂
与冷 NaOH 溶液反应：Cl₂ + 2NaOH → NaCl + NaClO + H₂O
With cold NaOH: Cl₂ + 2NaOH → NaCl + NaClO + H₂O
年表Timeline
- 1774
舍勒用盐酸与软锰矿制得氯气
Scheele makes chlorine from hydrochloric acid and pyrolusite
- 1810
戴维证明它是一种元素并命名为 chlorine（希腊语“黄绿色”）
Davy shows it is an element and names it chlorine, Greek for yellow-green
- 1890年代
电解食盐水的氯碱工业开始发展
The chlor-alkali industry based on brine electrolysis develops