📚 Reactions of Group 17 Elements | 第17族元素的反应
The Group 17 elements, known as the halogens (fluorine, chlorine, bromine, iodine, and astatine), are highly reactive non-metals. Their chemistry is dominated by the tendency to gain one electron to form halide ions (X⁻). This article systematically explores the characteristic reactions of the halogens, highlighting trends down the group and their practical applications, tailored to the Cambridge International A-Level Chemistry syllabus.
第17族元素，即卤素（氟、氯、溴、碘和砹），是高活性非金属。它们的化学性质主要表现为获取一个电子形成卤离子（X⁻）。本文系统探讨卤素的特征反应，突出族内递变规律及实际应用，贴合剑桥国际A-Level化学大纲。
1. Overview and Trends in Halogen Reactivity | 卤素反应性概述与趋势
reflected in their standard electrode potentials (e.g., F₂/F⁻ = +2.87 V, I₂/I⁻ = +0.54 V).
所有卤素都是强氧化剂，氧化性沿族向下递减：F₂ > Cl₂ > Br₂ > I₂。这反映在它们的标准电极电势上（如 F₂/F⁻ = +2.87 V，I₂/I⁻ = +0.54 V）。
The decrease in oxidising ability arises from increasing atomic radius, greater shielding, and hence a weaker attraction for an added electron, despite the exothermic electron affinity. Fluorine’s anomalously low F–F bond dissociation energy (due to lone-pair repulsion) also contributes to its extreme reactivity.
氧化能力下降源于原子半径增大、屏蔽效应增强，从而对额外电子的吸引力减弱，尽管电子亲和能放热。氟的F–F键解离能异常低（因孤对电子排斥），也是其极高反应性的原因之一。
Down Group 17, electronegativity falls (F 4.0, I 2.5), and bond energies of the hydrogen halides decrease, making the compounds easier to break down. These underlying properties govern the chemical behaviour of the halogens.
沿第17族向下，电负性下降（F 4.0，I 2.5），卤化氢的键能减小，使化合物更容易分解。这些基本性质决定了卤素的化学行为。
2. Reaction with Metals: Forming Ionic Halides | 与金属反应：形成离子型卤化物
Halogens react directly with most metals to produce ionic halides. The vigour decreases down the group. Fluorine attacks nearly all metals, often with ignition; chlorine reacts readily upon heating; bromine and iodine require stronger heating and may react more slowly.
卤素直接与大多数金属反应生成离子型卤化物。反应剧烈程度沿族向下递减。氟几乎可侵蚀所有金属，常伴有燃烧；氯加热下容易反应；溴和碘需要更强加热且反应较慢。
With sodium, chlorine burns with a bright yellow flame, forming white sodium chloride.
与钠反应时，氯气产生明亮的黄色火焰，生成白色氯化钠。
2Na(s) + Cl₂(g) → 2NaCl(s)
With aluminium, the reaction is vigorous, producing aluminium chloride.
与铝反应同样剧烈，生成氯化铝。
2Al(s) + 3Cl₂(g) → 2AlCl₃(s)
Iron reacts with chlorine to form iron(III) chloride, but with iodine only iron(II) iodide is produced, because iodine is a weaker oxidising agent.
铁与氯气反应生成氯化铁(III)，而与碘反应则只生成碘化铁(II)，因为碘是较弱的氧化剂。
2Fe(s) + 3Cl₂(g) → 2FeCl₃(s)
Fe(s) + I₂(g) → FeI₂(s)
3. Reaction with Hydrogen: Hydrogen Halides | 与氢气反应：卤化氢的生成
Halogens combine with hydrogen to form hydrogen halides (HX). The ease of reaction decreases dramatically down the group.
卤素与氢气化合生成卤化氢 (HX)。反应的容易程度沿族向下显著下降。
Fluorine reacts explosively with hydrogen even in the dark and at low temperatures.
氟即使在暗处和低温下也能与氢气发生爆炸性反应。
H₂(g) + F₂(g) → 2HF(g)
Chlorine reacts slowly in the dark but explosively when exposed to ultraviolet light or a spark. Bromine requires heating to above 200 °C, and iodine reacts only when heated strongly, establishing an equilibrium mixture.
氯气在暗处反应缓慢，但在紫外光或火花下会发生爆炸。溴需要加热到200 °C以上，碘仅在强热下反应且建立平衡混合物。
H₂(g) + Cl₂(g) → 2HCl(g)
H₂(g) + Br₂(g) ⇌ 2HBr(g)
H₂(g) + I₂(g) ⇌ 2HI(g)
The thermal stability of the hydrogen halides decreases from HF (very stable) to HI (decomposes easily). In aqueous solution, HF is a weak acid, while HCl, HBr and HI are strong acids.
卤化氢的热稳定性从 HF（非常稳定）到 HI（易分解）递减。在水溶液中，HF 是弱酸，而 HCl、HBr 和 HI 是强酸。
4. Reaction with Water: Disproportionation | 与水反应：歧化反应
Fluorine reacts vigorously with water, oxidising the oxygen rather than undergoing disproportionation.
氟与水的反应极为剧烈，它氧化水中的氧，而非发生歧化反应。
2F₂(g) + 2H₂O(l) → 4HF(aq) + O₂(g)
Chlorine, bromine and iodine undergo disproportionation in water, forming halide ions and hypohalous acids. The equilibrium lies well to the left, especially for iodine.
氯、溴和碘在水中发生歧化反应，生成卤离子和次卤酸。平衡强烈偏左，碘尤其如此。
Cl₂(g) + H₂O(l) ⇌ HCl(aq) + HOCl(aq)
Br₂(l) + H₂O(l) ⇌ HBr(aq) + HOBr(aq)
I₂(s) + H₂O(l) ⇌ HI(aq) + HOI(aq) (negligible)
Chlorine water is used as a disinfectant because hypochlorous acid (HOCl) kills bacteria. In bright sunlight, chlorine water
Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图