IB & WJEC Chemistry: Transition Metals – Key Facts | IB WJEC 化学：过渡金属考点精讲

📚 IB & WJEC Chemistry: Transition Metals – Key Facts | IB WJEC 化学：过渡金属考点精讲

Transition metals are central to understanding inorganic chemistry. They occupy the d-block of the periodic table, display variable oxidation states, form colourful compounds, and act as catalysts in many industrial and biological processes. This article distils the essential points required for IB and WJEC examination success.

过渡金属是理解无机化学的核心。它们位于周期表的d区，表现出可变的氧化态，形成有颜色的化合物，并在许多工业和生物过程中充当催化剂。本文提炼了IB和WJEC考试成功所需的基本要点。

1. Definition and Electron Configuration | 定义与电子排布

A transition metal is defined as an element that has an incomplete d subshell in either its atoms or in one or more of its common ions. In the first row of the d-block, scandium (Sc) and zinc (Zn) are not true transition metals because Sc³⁺ has the configuration [Ar] 3d⁰ and Zn²⁺ has [Ar] 3d¹⁰, both lacking partially filled d orbitals. Typical transition metals from Ti to Cu form ions with partially filled 3d orbitals, such as Fe²⁺ [Ar] 3d⁶ and Cu²⁺ [Ar] 3d⁹. Note the exceptional electron configurations of chromium and copper atoms: Cr [Ar] 3d⁵4s¹ and Cu [Ar] 3d¹⁰4s¹, which arise from the extra stability of half-filled and fully filled d subshells.

过渡金属定义为在其原子或一种或多种常见离子中具有未完全充满的d亚层的元素。在第一行d区元素中，钪(Sc)和锌(Zn)不是真正的过渡金属，因为Sc³⁺电子排布为[Ar] 3d⁰，Zn²⁺为[Ar] 3d¹⁰，二者均没有部分填充的d轨道。从钛(Ti)到铜(Cu)的典型过渡金属形成具有部分填充3d轨道的离子，如Fe²⁺ [Ar] 3d⁶和Cu²⁺ [Ar] 3d⁹。注意铬和铜原子的例外电子排布：Cr [Ar] 3d⁵4s¹和Cu [Ar] 3d¹⁰4s¹，这是由于半满和全满d亚层具有额外稳定性。

2. Physical Properties | 物理性质

Transition metals typically exhibit high melting points, high densities, and good electrical and thermal conductivity. This is due to strong metallic bonding arising from delocalised d and s electrons, which creates a rigid lattice. They are hard, malleable, and ductile, and they readily form alloys that often have enhanced properties.

过渡金属通常具有高熔点、高密度以及良好的导电性和导热性。这是由于离域的d和s电子形成了强金属键，构成了刚性晶格。它们坚硬、有延展性和韧性，并且容易形成合金，这些合金往往具有更优异的性能。

3. Variable Oxidation States | 多种氧化态

Unlike s-block metals that show only one or two oxidation states, transition metals can exist in multiple stable oxidation states. For instance, manganese ranges from +2 to +7 (Mn²⁺, MnO₄²⁻, MnO₄⁻), and iron commonly appears as +2 and +3. This variability is possible because the 3d and 4s electrons have very similar energies, allowing stepwise removal of electrons. The stability of higher oxidation states generally increases across a period when bound to strong oxidising agents like oxygen or fluorine.

与只表现一或两种氧化态的s区金属不同，过渡金属可以多种稳定的氧化态存在。例如，锰的氧化态可从+2到+7（Mn²⁺, MnO₄²⁻, MnO₄⁻），铁通常以+2和+3出现。这种可变性得以实现是因为3d和4s电子能量非常接近，允许电子逐步电离。在强氧化剂如氧或氟存在下，较高氧化态的稳定性通常沿周期递增。

4. Complex Formation | 配合物的形成

Transition metal ions act as Lewis acids, accepting lone pairs from ligands (Lewis bases) to form coordination complexes. Ligands may be monodentate, such as H₂O:, :NH₃, Cl⁻, or polydentate, like ethylenediamine (en) and EDTA⁴⁻. The coordination number is the number of donor atoms directly bonded to the central metal ion; the most common are 6 (octahedral) and 4 (tetrahedral or square planar). The complex ion is enclosed in square brackets, with the overall charge indicated outside.

过渡金属离子充当路易斯酸，接受来自配体（路易斯碱）的孤对电子以形成配位配合物。配体可以是单齿的，如 H₂O:、:NH₃、Cl⁻，也可以是多齿的，如乙二胺(en)和EDTA⁴⁻。配位数是直接与中心金属离子键合的供体原子数目；最常见的是6（八面体）和4（四面体或平面正方形）。配离子用方括号括起，整体电荷标在括号外。

5. Shapes of Complexes | 配合物的几何形状

The geometry of a complex depends on the coordination number and the metal’s electronic structure. Six-coordinate complexes are almost invariably octahedral, e.g. [Cu(H₂O)₆]²⁺ and [Fe(CN)₆]⁴⁻. Four-coordinate complexes can be tetrahedral, as in [CoCl₄]²⁻ and [ZnCl₄]²⁻, or square planar, typically for d⁸ metals like Pt²⁺ and Au³⁺, e.g. [Pt(NH₃)₂Cl₂]. Two-coordinate complexes (linear) are rare but found in [Ag(NH₃)₂]⁺.

配合物的几何构型取决于配位数和金属的电子结构。六配位配合物几乎都是八面体，例如 [Cu(H₂O)₆]²⁺ 和 [Fe(CN)₆]⁴⁻。四配位配合物可以是四面体，如 [CoCl₄]²⁻ 和 [ZnCl₄]²⁻，也可以是平面正方形，通常见于d⁸金属如Pt²⁺和Au³⁺，例如 [Pt(NH₃)₂Cl₂]。二配位配合物（直线形）罕见，但存在于 [Ag(NH₃)₂]⁺ 中。

6. Isomerism in Complexes | 配合物的异构现象

Transition metal complexes can display stereoisomerism. Geometrical (cis-trans) isomerism occurs in square planar and octahedral complexes that contain two different types of ligands in adjacent or opposite positions. Cisplatin, cis-[Pt(NH₃)₂Cl₂], is a powerful anticancer drug, while the trans isomer is pharmacologically inactive. Optical isomerism arises in octahedral complexes with three bidentate ligands, such as [Co(en)₃]³⁺, which exists as non-superimposable mirror images.

过渡金属配合物可以表现出立体异构现象。几何（顺反）异构发生在含有两种不同类型配体的平面正方形和八面体配合物中，它们处于相邻或相对位置。顺铂 cis-[Pt(NH₃)₂Cl₂] 是一种强效抗癌药物，而其反式异构体则无药理活性。光学异构出现在具有三个双齿配体的八面体配合物中，如 [Co(en)₃]³⁺，它们以不可重叠的镜像存在。

7. Colour of Transition Metal Compounds | 过渡金属化合物的颜色

The colour of transition metal complexes arises mainly from d-d electronic transitions. In an octahedral ligand field, the five d orbitals split into a lower-energy t₂_g set and a higher-energy e_g set. The energy gap Δ_o corresponds to the energy of visible light. When white light passes through the solution, photons of specific wavelengths are absorbed to promote an electron from the t₂_g to the e_g level. The transmitted light is the complementary colour of the absorbed light. For example, [Cu(H₂O)₆]²⁺ absorbs orange-red light and appears blue. If the d orbitals are empty (d⁰) or full (d¹⁰), no d-d transitions are possible and the compounds are typically colourless (e.g., Sc³⁺, Zn²⁺).

过渡金属配合物的颜色主要来源于d-d电子跃迁。在八面体配体场中，五个d轨道分裂为能量较低的t₂_g组和能量较高的e_g组。能隙Δ_o对应于可见光的能量。当白光通过溶液时，特定波长的光子被吸收，使电子从t₂_g能级跃迁到e_g能级。透射光是被吸收光的互补色。例如，[Cu(H₂O)₆]²⁺吸收橙红色光，显示蓝色。如果d轨道为空(d⁰)或全满(d¹⁰)，则无法发生d-d跃迁，化合物通常为无色（例如Sc³⁺、Zn²⁺）。