📚 Transition Metal Complexes: Isomerism, Ligand Substitution and Redox Titrations | 过渡金属配合物：异构、配体取代与氧化还原滴定
This revision guide brings together the key Edexcel A-Level Chemistry ideas on transition metals: d-block electron configurations, complex-ion formation, isomerism, ligand substitution, colour changes and redox titrations. It is designed for focused exam preparation and uses paired English–Chinese explanations to reinforce understanding.
本复习指南综合 Edexcel A-Level 化学过渡金属的核心考点：d 区电子构型、配离子形成、异构现象、配体取代、颜色变化和氧化还原滴定。内容采用英中对照讲解，适合考前集中复习和巩固理解。
1. Defining Transition Metals and d-Block Configurations | 过渡金属与 d 区电子构型
A transition metal is a d-block element that forms at least one stable ion with a partially filled d subshell. This definition excludes scandium and zinc: Sc³⁺ has the configuration 3d⁰, and Zn²⁺ has 3d¹⁰, so neither ion has a partially filled d orbital.
过渡金属是指能形成至少一种稳定离子且 d 亚层部分填充的 d 区元素。该定义将钪和锌排除：Sc³⁺ 的构型为 3d⁰，Zn²⁺ 为 3d¹⁰，因此这两种离子的 d 轨道都不是部分填充。
Iron is a typical transition metal. In its atomic state, Fe is [Ar]3d⁶4s², but the 4s electrons are lost before the 3d electrons when positive ions are formed.
铁是典型的过渡金属。Fe 原子电子构型为 [Ar]3d⁶4s²，但在形成阳离子时，4s 电子会先于 3d 电子失去。
Fe: [Ar]3d⁶4s² → Fe²⁺: [Ar]3d⁶ → Fe³⁺: [Ar]3d⁵
Copper and chromium show the expected stability of half-filled and fully filled d subshells: Cu is [Ar]3d¹⁰4s¹ and Cr is [Ar]3d⁵4s¹.
铜和铬体现了半充满和全充满 d 亚层的稳定性：Cu 为 [Ar]3d¹⁰4s¹，Cr 为 [Ar]3d⁵4s¹。
2. Complex Ions and Common Ligands | 配离子与常见配体
A complex ion consists of a central transition metal ion surrounded by ligands. A ligand is a Lewis base that donates a lone pair of electrons to form a coordinate bond with the metal ion.
配离子由中心过渡金属离子和周围配体组成。配体是路易斯碱，能够提供孤对电子与金属离子形成配位键。
Common monodentate ligands include water H₂O, ammonia NH₃, chloride Cl⁻, cyanide CN⁻ and hydroxide OH⁻. Bidentate ligands such as ethane-1,2-diamine H₂NCH₂CH₂NH₂ and ethanedioate C₂O₄²⁻ can form two coordinate bonds per ligand. EDTA⁴⁻ is a hexadentate ligand and forms six coordinate bonds.
常见的单齿配体包括水 H₂O、氨 NH₃、氯离子 Cl⁻、氰根 CN⁻ 和氢氧根 OH⁻。双齿配体如乙二胺 H₂NCH₂CH₂NH₂ 和草酸根 C₂O₄²⁻ 每个配体能形成两个配位键。EDTA⁴⁻ 是六齿配体，可形成六个配位键。
| Ligand | Denticity | Example complex |
|---|---|---|
| H₂O | monodentate | [Cu(H₂O)₆]²⁺ |
| Cl⁻ | monodentate | [CoCl₄]²⁻ |
| NH₃ | monodentate | [Cu(NH₃)₄(H₂O)₂]²⁺ |
| ethane-1,2-diamine | bidentate | [Ni(en)₃]²⁺ |
| EDTA⁴⁻ | hexadentate | [Cu(EDTA)]²⁻ |
3. Coordination Number and Shapes | 配位数与空间构型
The coordination number is the number of coordinate bonds formed by the ligands to the central metal ion. A six-coordinate complex is usually octahedral with bond angles of 90°.
配位数是指配体与中心金属离子形成的配位键数目。六配位配合物通常为八面体，键角为 90°。
Four-coordinate complexes can be tetrahedral, as in [CoCl₄]²⁻, or square planar, as in cisplatin [PtCl₂(NH₃)₂]. The shape depends on the metal ion and ligand field.
四配位配合物可以是四面体，如 [CoCl₄]²⁻，也可以是平面正方形，如顺铂 [PtCl₂(NH₃)₂]。具体构型取决于金属离子和配体场。
Two-coordinate complexes, such as [Ag(NH₃)₂]⁺, are linear. In Edexcel questions, you must link coordination number to the observed shape and bond angle.
二配位配合物，例如 [Ag(NH₃)₂]⁺，为直线形。在 Edexcel 考题中，必须将配位数与观察到的构型和键角联系起来。
4. Naming Complexes and Working Out Oxidation States | 配合物命名与氧化态计算
When naming a complex ion, ligands are named before the metal. Anionic ligands end in -o, such as chloride becoming chlorido and cyanide becoming cyanido. The metal oxidation state is shown in Roman numerals after the metal name.
命名配离子时，配体名称在前，金属名称在后。阴离子配体以 -o 结尾，例如 chloride 变为 chlorido，cyanide 变为 cyanido。金属氧化态用罗马数字写在金属名称之后。
ex equals the overall charge. For [CuCl₄]²⁻, let Cu = x, so x + 4(−1) = −2, giving x = +2.
计算金属氧化态时，利用配合物中各元素氧化态之和等于总电荷。对于 [CuCl₄]²⁻，设 Cu 为 x，则 x + 4(−1) = −2，解得 x = +2。
In [Fe(H₂O)₆]³⁺, water is neutral, so Fe is +3. This is useful when writing half-equ
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