📚 Transition Metals in IGCSE Edexcel Chemistry | IGCSE Edexcel 化学：过渡金属 考点精讲
Transition metals sit in the middle of the Periodic Table and show a set of properties that make them distinct from the metals in Groups 1 and 2. In the IGCSE Edexcel Chemistry specification, you are expected to recall their key features – variable valency, coloured compounds, catalytic activity, and the ability to form complex ions. This article guides you through every essential point, pairing explanations with typical exam questions.
过渡金属位于周期表的中央区域，表现出一系列与第1族、第2族金属截然不同的性质。在IGCSE Edexcel化学考试中，你需要记住它们的关键特征——可变化合价、有色化合物、催化活性以及形成配合离子的能力。本文带你梳理每一个必考要点，将原理解析与典型考题紧密结合。
1. What Are Transition Metals? | 过渡金属是什么？
Transition metals are elements that form at least one stable ion with a partially filled d subshell. In simpler IGCSE terms, they are the metallic elements found in the central block of the Periodic Table, between Group 2 and Group 3. Typical examples include iron (Fe), copper (Cu), manganese (Mn), chromium (Cr), nickel (Ni) and zinc (Zn) – though zinc is often treated as an exception because its ions have a full d subshell.
过渡金属是指至少能形成一种具有部分填充d亚层稳定离子的元素。用更简单的IGCSE语言说，它们就是位于周期表中部、第2族和第3族之间的金属元素。常见例子包括铁(Fe)、铜(Cu)、锰(Mn)、铬(Cr)、镍(Ni)和锌(Zn)——尽管锌常被当作例外，因为它的离子d亚层是全满的。
These elements share common properties: they are hard, dense, have high melting points, exhibit variable oxidation states, and often act as catalysts. Their compounds are frequently coloured, which makes them easy to spot in test tubes.
这些元素具有以下共同性质：质地坚硬、密度大、熔点高、表现出可变氧化态，并且常常充当催化剂。它们的化合物通常带有颜色，在试管中非常容易辨认。
2. Position in the Periodic Table | 在周期表中的位置
In the Periodic Table, transition metals are located in the d-block, between Groups 2 and 13 (old numbering IIA and IIIA). The first row of transition metals runs from scandium to zinc. For IGCSE, you only need to know the positions and symbols of the most common ones: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn. Remember that mercury (Hg) is also a transition metal, but its unusual properties (liquid at room temperature) are a consequence of its large atomic size and relativistic effects.
在周期表中，过渡金属位于d区，介于第2族与第13族（旧编号IIA和IIIA）之间。第一行过渡金属从钪到锌。在IGCSE中你只需记住最常见过渡金属的位置和符号：Sc、Ti、V、Cr、Mn、Fe、Co、Ni、Cu和Zn。记住汞(Hg)也是过渡金属，但它在室温下为液态这一反常性质源于其较大的原子半径和相对论效应。
Being in the middle of the Periodic Table, transition metals bridge the highly reactive s-block metals and the less reactive p-block metals. Their electron configurations end in (n−1)d and ns orbitals, which explains why they can lose different numbers of electrons.
过渡金属位于周期表中央，搭建了高活性的s区金属与活性较低的p区金属之间的桥梁。它们的电子排布以(n−1)d和ns轨道结尾，这也解释了为什么它们能失去不同数量的电子。
3. Physical Properties | 物理性质
Transition metals are typically hard, strong, and have high densities. For example, iron has a density of 7.87 g cm⁻³ and copper 8.96 g cm⁻³, while Group 1 metals like sodium float on water. Their high melting points – iron melts at 1538 °C, copper at 1085 °C – make them suitable for high-temperature applications such as engine parts and construction.
过渡金属通常坚硬、强度高且密度大。例如铁的密度为7.87 g cm⁻³，铜为8.96 g cm⁻³，而钠等第1族金属则能浮在水面上。它们的高熔点——铁1538 °C，铜1085 °C——使它们适用于发动机零件和建筑等高温环境。
They are also good conductors of heat and electricity. This is due to the presence of delocalised electrons from both the 4s and 3d orbitals, which can move freely throughout the metallic lattice. Malleability and ductility allow them to be hammered into sheets or drawn into wires without breaking.
它们也是热和电的良导体。这是因为来自4s和3d轨道的离域电子可以在金属晶格中自由移动。延展性和韧性使得它们能够被锤打成薄片或拉成丝而不断裂。
The characteristic metallic bonding in transition metals involves a strong attraction between positive metal ions and a sea of delocalised electrons. Because more electrons are donated (from both s and d orbitals), the metallic bonds are stronger than those in Group 1 or 2 metals, resulting in higher hardness and melting points.
过渡金属中特有的金属键涉及带正电的金属离子与离域电子海之间的强吸引力。由于贡献的电子更多（来自s和d轨道），金属键比第1族或第2族金属中的更强，因此硬度更高、熔点也更高。
4. Variable Oxidation States | 可变氧化态
One of the defining features of transition metals is their ability to exist in more than one oxidation state. For instance, iron forms Fe²⁺ and Fe³⁺ ions; copper forms Cu⁺ and Cu²⁺; manganese can range from +2 to +7, most famously in MnO₄⁻ where manganese is in the +7 state. This contrasts with Group 1 metals which only have a +1 oxidation state and Group 2 metals which only have +2.
过渡金属的一个关键特征就是它们能以多种氧化态存在。例如铁能形成Fe²⁺和Fe³⁺离子；铜能形成Cu⁺和Cu²⁺；锰的氧化态范围可从+2到+7，最著名的例子是MnO₄⁻中锰为+7态。这与第1族金属只有+1态、第2族金属只有+2态形成了鲜明对比。
The ability to vary oxidation states arises because the energy levels of the 4s and 3d electrons are close together. Transition metal atoms can lose electrons from both the 4s and 3d subshells successively, resulting in different stable cations. This property is essential in redox chemistry and in the role of transition metals as catalysts.
氧化态可变的原因在于4s和3d电子的能级非常接近。过渡金属原子可以依次失去4s和3d亚层的电子，形成不同的稳定阳离子。这一性质在氧化还原化学以及过渡金属的催化作用中都至关重要。
| Element | Common Oxidation States | Example Ion / Compound |
|---|---|---|
| Iron (Fe) | +2, +3 | FeCl₂, FeCl₃ |
| Copper (Cu) | +1, +2 | Cu₂O, CuO |
| Manganese (Mn) | +2, +4, +7 | MnSO₄, MnO₂, KMnO₄ |
| Chromium (Cr) | +3, +6 | CrCl₃, K₂Cr₂O₇ |
5. Formation of Coloured Compounds | 形成有色化合物
Compounds and aqueous ions of transition metals are often vividly coloured. For IGCSE, you must know that Cu²⁺(aq) is blue, Fe²⁺(aq) is pale green, Fe³⁺(aq) is orange-brown, MnO₄⁻(aq) is purple, and Cr₂O₇²⁻(aq) is orange. The colour arises because the partially filled d orbitals absorb visible light; an electron is promoted from a lower d orbital to a higher one, and the wavelength not absorbed is the colour we see.
过渡金属的化合物和水合离子常常具有鲜艳的颜色。在IGCSE中你必须知道：Cu²⁺(aq) 是蓝色，Fe²⁺(aq) 是浅绿色，Fe³⁺(aq) 是橙棕色，MnO₄⁻(aq) 是紫色，Cr₂O₇²⁻(aq) 是橙色。颜色的产生是因为部分填充的d轨道吸收可见光；电子从较低d轨道跃迁到较高d轨道，未被吸收的波长即为我们看到的颜色。
This is in sharp contrast to compounds of Group 1 and Group 2 metals, which are mostly white or colourless because their ions have either a full subshell or no d electrons at all. Therefore, observing a colour change in a test tube is often a quick way to spot a transition metal reaction.
这与第1族和第2族金属的化合物形成鲜明对比，后者的离子要么是全满亚层要么根本没有d电子，因此它们大多呈白色或无色。因此，在试管中观察到颜色变化常常是快速识别过渡金属反应的方法。
6. Catalytic Properties | 催化性质
Transition metals and their compounds are widely used as catalysts in industrial processes. They work by providing a surface on which reactant molecules can adsorb, forming temporary bonds with the d electrons. This lowers the activation energy. Key examples you must recall for IGCSE Edexcel are:
过渡金属及其化合物在工业过程中被广泛用作催化剂。它们通过提供表面使反应物分子吸附在其上，与d电子形成临时化学键，从而降低活化能。IGCSE Edexcel考试中你必须牢记的例子包括：
- Iron in the Haber process for ammonia synthesis: N₂ + 3H₂ ⇌ 2NH₃
- Vanadium(V) oxide (V₂O₅) in the Contact process for sulfuric acid: 2SO₂ + O₂ ⇌ 2SO₃
- Manganese(IV) oxide (MnO₂) in the decomposition of hydrogen peroxide: 2H₂O₂ → 2H₂O + O₂
- Nickel in the hydrogenation of alkenes (margarine production): alkene + H₂ → alkane
- Platinum/rhodium in catalytic converters for cars: 2CO + 2NO → 2CO₂ + N₂
- 铁在哈伯法合成氨中：N₂ + 3H₂ ⇌ 2NH₃
- 五氧化二钒(V₂O₅)在接触法制硫酸中：2SO₂ + O₂ ⇌ 2SO₃
- 二氧化锰(MnO₂)在过氧化氢分解中：2H₂O₂ → 2H₂O + O₂
- 镍在烯烃加氢（人造黄油生产）中：烯烃 + H₂ → 烷烃
- 铂/铑在汽车催化转化器中：2CO + 2NO → 2CO₂ + N₂
The variable oxidation state of transition metals allows them to act as ‘electron banks’ – accepting and releasing electrons during the catalytic cycle, which no Group 1 or 2 metal can do.
过渡金属的可变氧化态使它们成为“电子银行”——在催化循环中接收和释放电子，这是任何第1族或第2族金属都无法做到的。
7. Complex Ion Formation | 配合物离子的形成
Transition metal ions in aqueous solution are usually surrounded by water molecules acting as ligands, forming complex ions. A ligand is a molecule or ion that donates a lone pair of electrons to the central metal ion, forming a coordinate bond. For example, Cu²⁺ forms the blue hexaaquacopper(II) ion, [Cu(H₂O)₆]²⁺, and Fe²⁺ forms the pale green [Fe(H₂O)₆]²⁺.
水溶液中的过渡金属离子通常被作为配体的水分子包围，形成配合物离子。配体是指能提供孤对电子给中心金属离子、形成配位键的分子或离子。例如，Cu²⁺形成蓝色的六水合铜(II)离子 [Cu(H₂O)₆]²⁺；Fe²⁺形成浅绿色的 [Fe(H₂O)₆]²⁺。
IGCSE candidates are expected to describe the test for transition metal ions using sodium hydroxide solution, where the coloured hydroxide precipitates form. With excess ammonia solution, some precipitates redissolve to form deep-coloured complex ions, such as the deep blue tetraamminecopper(II) ion, [Cu(NH₃)₄(H₂O)₂]²⁺. This dissolution is a characteristic property of certain transition metal hydroxides.
IGCSE考生需要描述用氢氧化钠溶液检验过渡金属离子的方法，生成有色氢氧化物沉淀。当加入过量氨水时，某些沉淀会重新溶解，形成深色配合物离子，例如深蓝色的四氨合铜(II)离子 [Cu(NH₃)₄(H₂O)₂]²⁺。这种溶解是某些过渡金属氢氧化物的特征性质。
8. Comparison with Group 1 Metals | 与第1族金属的比较
The differences between transition metals and Group 1 metals are frequently tested in IGCSE. While both are metals, they behave almost oppositely in terms of density, hardness, melting point, reactivity, catalytic ability, and variety of oxidation states. The table below summarises these contrasts:
过渡金属与第1族金属的差异是IGCSE的常考知识点。虽然两者都是金属，它们在密度、硬度、熔点、反应活性、催化能力以及氧化态多样性等方面几乎完全相反。下表总结了这些对比：
| Property | Group 1 (e.g. Na) | Transition (e.g. Fe) |
|---|---|---|
| Hardness | Soft, can be cut with a knife | Hard, strong |
| Density | Low (floats on water) | High |
| Melting point | Low (Na 98 °C) | High (Fe 1538 °C) |
| Reactivity | Very reactive, especially with water | Much less reactive; Fe rusts slowly, Cu unreactive with water |
| Oxidation states | Only +1 | Multiple, e.g. Fe²⁺ and Fe³⁺ |
| Colour of compounds | White or colourless | Often coloured |
| Catalytic activity | No significant catalytic use | Widely used as catalysts |
In short, the chemical behaviour differences originate from the electronic structure: Group 1 metals have a single s electron that is easily lost, while transition metals have inner d electrons that participate in bonding and allow for more complex chemistry.
简而言之，化学行为的差异源自电子结构的差异：第1族金属只有一个容易失去的s电子，而过渡金属拥有内层d电子参与成键，使得化学反应更为复杂多样。
9. Important Transition Metals and Their Compounds | 重要的过渡金属及其化合物
The exam expects you to know specific reactions and appearances of key transition metal compounds.
考试要求你掌握关键过渡金属化合物的具体反应和外观特征。
Iron: Pure iron is extracted from its oxide ores using a blast furnace. The main reactions involve reduction with carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂. Rusting of iron requires both oxygen and water: 4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O. Iron(II) sulfate (FeSO₄) is pale green; iron(III) chloride (FeCl₃) is yellow-brown.
铁：纯铁由铁氧化物矿石在高炉中冶炼得到。主要反应涉及一氧化碳还原：Fe₂O₃ + 3CO → 2Fe + 3CO₂。铁生锈需要氧气和水同时存在：4Fe + 3O₂ + 2xH₂O → 2Fe₂O₃·xH₂O。硫酸亚铁(FeSO₄)呈浅绿色；氯化铁(FeCl₃)呈黄棕色。
Copper: Copper is purified by electrolysis. Copper(II) oxide (CuO) is black and reacts with dilute sulfuric acid to give blue copper(II) sulfate solution: CuO + H₂SO₄ → CuSO₄ + H₂O. On heating, blue hydrated copper(II) sulfate crystals turn white as they lose water: CuSO₄·5H₂O → CuSO₄ + 5H₂O.
铜：铜通过电解精炼。氧化铜(CuO)呈黑色，与稀硫酸反应生成蓝色硫酸铜溶液：CuO + H₂SO₄ → CuSO₄ + H₂O。蓝色五水合硫酸铜晶体加热后会因失水变为白色：CuSO₄·5H₂O → CuSO₄ + 5H₂O。
Manganese: Potassium manganate(VII) (KMnO₄) is a powerful oxidising agent, used in red-ox titrations because it acts as its own indicator – the purple colour disappears when it reacts. Manganese(IV) oxide is a black powder used as a catalyst for H₂O₂ decomposition.
锰：高锰酸钾(KMnO₄)是强氧化剂，在氧化还原滴定中被用作自身指示剂——反应时紫色会消失。二氧化锰(MnO₂)是黑色粉末，用作过氧化氢分解的催化剂。
Chromium: Potassium dichromate(VI) (K₂Cr₂O₇) is an orange oxidising agent, used in tests for alcohols (colour change to green Cr³⁺). Chromium(III) compounds are usually green.
铬：重铬酸钾(K₂Cr₂O₇)是橙色氧化剂，用于醇的检验（颜色变为绿色的Cr³⁺）。铬(III)化合物通常呈绿色。
10. Uses and Alloys | 用途与合金
Because of their strength, resistance to corrosion, and ability to form alloys with improved properties, transition metals are indispensable in modern life. Iron is alloyed with carbon and other elements to make steel, which is used in construction, vehicles, and machinery. Stainless steel contains iron, chromium, and nickel – the chromium forms a protective oxide layer that prevents rusting.
由于强度大、耐腐蚀以及能够形成性能改良的合金，过渡金属在现代生活中不可或缺。铁与碳及其他元素形成钢，用于建筑、车辆和机械。不锈钢含有铁、铬和镍——铬形成保护性氧化层防止生锈。
Copper is used in electrical wiring due to its excellent conductivity and ductility. Its alloys include brass (copper-zinc) and bronze (copper-tin). Titanium is valued for its low density and high strength, widely used in aircraft and medical implants. Chromium is also applied as a protective and decorative plating on other metals.
铜因导电性和延展性优异而用于电线。它的合金包括黄铜（铜-锌）和青铜（铜-锡）。钛因低密度和高强度而被广泛应用于航空和医疗植入物。铬还常作为装饰性和保护性镀层覆盖于其他金属表面。
The catalytic properties of transition metals themselves also represent a major industrial use – without iron, we would not have affordable fertilisers; without platinum, our car exhaust would be far more polluting.
过渡金属的催化性质本身就是一项重要的工业应用——没有铁就没有廉价的化肥；没有铂，汽车尾气将造成严重得多的污染。
11. Tests for Transition Metal Ions | 过渡金属离子的检验
Sodium hydroxide and ammonia solutions are the two key reagents used to identify transition metal ions in the laboratory. Adding a few drops of NaOH to a solution containing a transition metal ion produces a characteristic coloured precipitate. Adding excess ammonia can sometimes redissolve the precipitate to give a deep-coloured complex ion. The table below summarises the observations you must memorise:
氢氧化钠和氨水是实验室中鉴别过渡金属离子的两种关键试剂。将少量NaOH滴加到含有过渡金属离子的溶液中，会生成特征颜色的沉淀。加入过量氨水有时能重新溶解沉淀，形成深色配合物离子。下表总结了你必须牢记的观察结果：
| Metal ion | With NaOH (few drops) | With excess NH₃(aq) |
|---|---|---|
| Cu²⁺ | Blue precipitate, Cu(OH)₂ | Redissolves to deep blue solution |
| Fe²⁺ | Dirty green precipitate, Fe(OH)₂ that turns brown at the surface on standing | Insoluble, no further change |
| Fe³⁺ | Red-brown precipitate, Fe(OH)₃ | Insoluble |
| Mn²⁺ | Pale pink precipitate, Mn(OH)₂ that darkens in air | Insoluble |
| Cr³⁺ | Grey-green precipitate, Cr(OH)₃ | Redissolves to green solution |
These test results are explained by the formation of hydroxides, which are insoluble in water. Some of these hydroxides can act as acids in the presence of excess ammonia, forming soluble complex ions by ligand exchange.
这些检验结果的原因在于生成了不溶于水的氢氧化物。其中某些氢氧化物在过量氨水中可以充当酸，通过配体交换形成可溶的配合物离子。
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