Transition Metals and Complex Ions | 过渡金属与配位离子

📚 Transition Metals and Complex Ions | 过渡金属与配位离子

Transition metal chemistry brings together atomic structure, bonding and redox ideas studied at AS level. For Edexcel A-Level Chemistry, Topic 15 focuses on the d-block elements, their complex ions, variable oxidation states, catalytic action and colourful compounds. This article explains the key ideas with worked examples and exam-style summaries.

过渡金属化学将 AS 阶段学习的原子结构、化学键和氧化还原概念结合在一起。在 Edexcel A-Level 化学中，Topic 15 的重点是 d 区元素、它们的配离子、可变的氧化态、催化作用以及颜色丰富的化合物。本文通过例题和考试风格总结解释这些核心概念。

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1. d-Block Elements and Electron Configurations | d 区元素与电子构型

The d-block consists of elements from scandium to zinc, where the 3d orbitals are progressively filled. In the first transition series, the 4s orbital is filled before the 3d orbitals, so potassium and calcium build the 4s shell first.

d 区包括从钪到锌的元素，它们的 3d 轨道逐步被填充。在第一过渡系中，4s 轨道先于 3d 轨道被填充，因此钾和钙先填充 4s 层。

Two atoms show unusual configurations: chromium is [Ar] 3d⁵ 4s¹ rather than [Ar] 3d⁴ 4s², and copper is [Ar] 3d¹⁰ 4s¹ rather than [Ar] 3d⁹ 4s². This arises because a half-filled or completely filled d sub-shell has extra stability.

两个原子表现出特殊构型：铬是 [Ar] 3d⁵ 4s¹ 而不是 [Ar] 3d⁴ 4s²，铜是 [Ar] 3d¹⁰ 4s¹ 而不是 [Ar] 3d⁹ 4s²。这是因为半充满或全充满的 d 亚层具有额外的稳定性。

Element | 元素	Atomic number | 原子序数	Electron configuration | 电子构型
Sc	21	[Ar] 3d¹ 4s²
Ti	22	[Ar] 3d² 4s²
V	23	[Ar] 3d³ 4s²
Cr	24	[Ar] 3d⁵ 4s¹
Mn	25	[Ar] 3d⁵ 4s²
Fe	26	[Ar] 3d⁶ 4s²
Co	27	[Ar] 3d⁷ 4s²
Ni	28	[Ar] 3d⁸ 4s²
Cu	29	[Ar] 3d¹⁰ 4s¹
Zn	30	[Ar] 3d¹⁰ 4s²

When transition metals form positive ions, electrons are removed from the 4s orbital before the 3d orbitals. For example, Fe²⁺ has the configuration [Ar] 3d⁶ and Cr³⁺ is [Ar] 3d³.

当过渡金属形成正离子时，电子先从 4s 轨道失去，再失去 3d 轨道电子。例如，Fe²⁺ 的构型是 [Ar] 3d⁶，Cr³⁺ 是 [Ar] 3d³。

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2. What Makes a Transition Metal? | 过渡金属的定义

A transition metal is defined as a d-block element that forms at least one stable ion with an incomplete d sub-shell. This definition excludes scandium and zinc because Sc³⁺ has a d⁰ configuration and Zn²⁺ has a d¹⁰ configuration.

过渡金属的定义是：能形成至少一种稳定离子且该离子的 d 亚层未充满的 d 区元素。这一定义排除了钪和锌，因为 Sc³⁺ 的 d 亚层为 d⁰，Zn²⁺ 为 d¹⁰。

Variable oxidation states arise because the 3d and 4s electrons are close in energy, allowing different numbers of electrons to be lost in bonding. Iron, for example, forms both Fe²⁺ and Fe³⁺, while manganese can form Mn²⁺, MnO₂, MnO₄²⁻ and MnO₄⁻.

可变的氧化态之所以出现，是因为 3d 和 4s 电子能量接近，可以在成键时失去不同数量的电子。例如铁可以形成 Fe²⁺ 和 Fe³⁺，而锰可以形成 Mn²⁺、MnO₂、MnO₄²⁻ 和 MnO₄⁻。

Transition metals also form coloured compounds, complex ions and act as catalysts, all linked to partially filled d orbitals. These properties are much less common in s-block and p-block metals.

过渡金属还能形成有色化合物、配离子并用作催化剂，这些性质都与部分填充的 d 轨道有关。这些性质在 s 区和 p 区金属中较少见。

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3. Complex Ions and Ligands | 配离子与配体

A ligand is a molecule or negative ion that donates a lone pair of electrons to a central metal ion to form a coordinate bond. A complex ion contains a central transition metal ion surrounded by ligands.

配体是能提供孤对电子给中心金属离子形成配位键的分子或负离子。配离子由中心过渡金属离子和围绕其周围的配体组成。

Common monodentate ligands donate one lone pair each. Examples include water H₂O, ammonia NH₃, chloride Cl⁻, hydroxide OH⁻ and cyanide CN⁻. Each ligand must have at least one lone pair available for donation.

常见的单齿配体各提供一个孤对电子。例子包括水 H₂O、氨 NH₃、氯离子 Cl⁻、氢氧根 OH⁻ 和氰根 CN⁻。每种配体必须至少有一对孤对电子可用于配位。

Bidentate ligands donate two lone pairs from two different atoms. Ethane-1,2-diamine, often written as en, has the formula H₂NCH₂CH₂NH₂. The ethanedioate ion C₂O₄²⁻ is another bidentate ligand. Multidentate ligands such as EDTA⁴⁻ can form six coordinate bonds.

双齿配体由两个不同原子各提供一对孤对电子。乙二胺通常写作 en，分子式为 H₂NCH₂CH₂NH₂。乙二酸根离子 C₂O₄²⁻ 是另一种双齿配体。多齿配体如 EDTA⁴⁻ 可以形成六个配位键。

In a coordinate bond, the ligand is the electron-pair donor and the metal ion is the electron-pair acceptor. The bond is shown with an arrow from the ligand to the metal centre.

在配位键中，配体是电子对给体，金属离子是电子对受体。配位键常用从配体指向金属中心的箭头表示。

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4. Coordination Number and Shapes | 配位数与空间构型

The coordination number is the number of coordinate bonds formed between the central metal ion and its ligands. The most common coordination numbers are 6 and 4, but 2 and 5 also occur in some complexes.

配位数是中心金属离子与配体之间形成的配位键数目。最常见的配位数是 6 和 4，但某些配合物也会出现 2 和 5。

Six-coordinate complexes are usually octahedral, with bond angles of 90°. A typical example is [Cu(H₂O)₆]²⁺, in which six water molecules surround the copper(II) ion.

六配位的配合物通常为八面体形，键角为 90°。典型例子是 [Cu(H₂O)₆]²⁺，其中六个水分子包围铜(II)离子。

Four-coordinate complexes can be tetrahedral with bond angles of 109.5°, such as [CuCl₄]²⁻. They can also be square planar with bond angles of 90°, such as [Ni(CN)₄]²⁻ and cis-platin.

四配位的配合物可以是四面体形，键角为 109.5°，例如 [CuCl₄]²⁻。也可以是平面正方形，键角为 90°，例如 [Ni(CN)₄]²⁻ 和顺铂。

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