📚 A-Level Chemistry: Halogens and Their Compounds | A-Level化学：卤素及其化合物的用途
The halogens make up Group 17 of the periodic table: fluorine, chlorine, bromine, iodine and astatine. Their chemical behaviour is dominated by the need to gain one electron, forming halide ions X⁻. This strong oxidising ability is the reason why so many halogen-containing compounds are useful in commerce, industry, medicine and daily life.
卤素是元素周期表第17族中的氟、氯、溴、碘和砹。它们的化学行为以夺取一个电子、生成卤离子 X⁻ 为主导。这种强氧化性是众多含卤化合物广泛用于工业、商业、医药和日常生活的根本原因。
1. The Halogens at a Glance | 卤素概览
At room temperature, fluorine is a pale yellow gas, chlorine is a pale green gas, bromine is a red-brown liquid, and iodine is a grey-black solid. All exist as diatomic molecules: F₂, Cl₂, Br₂ and I₂.
在室温下，氟是淡黄色气体，氯是黄绿色气体，溴是红棕色液体，碘是灰黑色固体。它们都以双原子分子存在：F₂、Cl₂、Br₂ 和 I₂。
The outer-shell configuration of the halogens is ns²np⁵, and their chemistry is dominated by the half-equation:
卤素的外层电子构型为 ns²np⁵，它们的化学性质主要来自下面这个半反应：
X₂ + 2e⁻ → 2X⁻
The oxidising power and electronegativity decrease down the group. Thus chlorine can displace bromide and iodide ions, and bromine can displace iodide ions.
氧化能力和电负性自上而下减弱。因此氯可以置换溴离子和碘离子，溴可以置换碘离子。
| Halogen | State at room temperature | Principal uses |
| F₂ | Pale yellow gas | UF
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