Transition Metals: Variable Oxidation States, Complex Ions and Catalysis | 过渡金属：可变化合价、配位离子与催化作用

📚 Transition Metals: Variable Oxidation States, Complex Ions and Catalysis | 过渡金属：可变化合价、配位离子与催化作用

Transition metals are a central topic in Edexcel A Level Chemistry because they link electronic structure, redox, bonding, colour and catalysis. Students often find them challenging because one metal can show several oxidation states, form numerous coloured complexes and act as a catalyst.

过渡金属是 Edexcel A Level 化学的核心主题，因为它们把电子结构、氧化还原、成键、颜色和催化联系起来。学生常觉得困难，因为同一种金属可以表现多种氧化态、形成多种有色配合物并起催化作用。

This article covers the essential definitions, electron configurations, variable oxidation states, complex-ion chemistry, colour, isomerism and catalytic behaviour. It also gives Edexcel-style exam tips to help you write precise, credited answers.

本文涵盖基本定义、电子排布、可变化合价、配位离子化学、颜色、同分异构和催化行为，并提供 Edexcel 风格应试技巧，帮助你写出准确、能得分的答案。

1. Definition and Position of Transition Metals | 过渡金属的定义与位置

A transition metal is a d-block element that forms at least one stable ion with an incomplete d-subshell. This definition is important because it excludes zinc and scandium, even though they are found in the d-block of the Periodic Table.

过渡金属是指 d 区元素中至少能形成一种稳定离子且该离子 d 亚层未充满的元素。这个定义很重要，因为它排除了锌和钪，尽管它们位于元素周期表的 d 区。

Scandium forms Sc³⁺ with an empty 3d-subshell, while zinc forms Zn²⁺ with a full 3d¹⁰ configuration. Neither has a partially filled d-subshell in its common ion, so they are not classed as transition metals under the IUPAC definition.

钪形成 Sc³⁺ 时 3d 亚层全空，锌形成 Zn²⁺ 时 3d¹⁰ 全满。它们的常见离子都没有未充满的 d 亚层，因此根据 IUPAC 定义不属于过渡金属。

The first-row transition metals from titanium to copper are the main focus at A Level. Their properties arise because the 3d and 4s orbitals are close in energy, allowing d-electrons to participate in bonding and redox reactions.

第一行过渡金属从钛到铜是 A Level 的重点。它们的性质来源于 3d 和 4s 轨道能量接近，使 d 电子能够参与成键和氧化还原反应。

2. Electron Configurations of Atoms and Ions | 原子和离子的电子排布

In neutral transition metal atoms, the 4s orbital is occupied before the 3d orbitals. However, when positive ions are formed, electrons are removed from 4s before 3d because the 4s electrons become higher in energy than the 3d electrons once the atom is ionised.

中性过渡金属原子中，4s 轨道先于 3d 轨道填充。但形成正离子时，电子先由 4s 失去，因为原子电离后 4s 电子能量高于 3d 电子。

For example, iron has the electron configuration Fe [Ar] 3d⁶ 4s². The Fe²⁺ ion is [Ar] 3d⁶, and Fe³⁺ is [Ar] 3d⁵. You must be able to write both atom and ion configurations using noble-gas shorthand.

例如，铁的电子排布为 Fe [Ar] 3d⁶ 4s²。Fe²⁺ 离子为 [Ar] 3d⁶，Fe³⁺ 为 [Ar] 3d⁵。你必须能用惰性气体简写写出原子和离子的电子排布。

Chromium and copper are exceptions because a half-filled or fully filled d-subshell gives extra stability. Chromium is [Ar] 3d⁵ 4s¹ rather than [Ar] 3d⁴ 4s², and copper is [Ar] 3d¹⁰ 4s¹ rather than [Ar] 3d⁹ 4s².

铬和铜是例外，因为半满或全满 d 亚层具有额外稳定性。铬的排布为 [Ar] 3d⁵ 4s¹ 而不是 [Ar] 3d⁴ 4s²；铜为 [Ar] 3d¹⁰ 4s¹ 而不是 [Ar] 3d⁹ 4s²。

When writing equations for redox reactions, keep electron configurations in mind. The loss of 4s electrons first explains why many transition metals have +2 oxidation states, while further loss of 3d electrons gives higher states such as +3, +4, +6 and +7.

书写氧化还原方程式时要牢记电子排布。4s 电子先失去解释了为什么许多过渡金属有 +2 氧化态，而进一步失去 3d 电子则产生 +3、+4、+6 和 +7 等更高氧化态。

3. Variable Oxidation States | 可变化合价

Transition metals show variable oxidation states because the energy difference between the 4s and 3d electrons is small. As a result, different numbers of electrons can be removed under different conditions, producing different ions and compounds.

过渡金属表现出可变化合价，因为 4s 和 3d 电子能量差很小。因此在不同条件下可以失去不同数目的电子，形成不同的离子和化合物。

Manganese is the classic example, with oxidation states ranging from +2 in Mn²⁺ to +7 in MnO₄⁻. The +7 state is strongly oxidising, while the +2 state is the most stable under acidic aqueous conditions.

锰是最典型的例子，氧化态从 Mn²⁺ 的 +2 到 MnO₄⁻ 的 +7。+7 态具有强氧化性，而 +2 态在酸性水溶液中最稳定。

The table below summarises common oxidation states of vanadium and manganese, including typical colours.

下表总结了钒和锰的常见氧化态及典型颜色。