📚 3 First-Row D-Block Elements (HL) | 第一行d区元素 (HL)
The first-row d-block elements, comprising scandium through zinc, are the cornerstones of transition metal chemistry. The progressive filling of the 3d sublevel across this period gives rise to a remarkable set of properties: variable oxidation states, vivid colours in aqueous solutions, paramagnetism, extensive catalytic behaviour, and the ability to form stable complex ions. In IB Chemistry at Higher Level, a deep exploration of these elements unlocks an understanding of electron configuration subtleties, stereoisomerism in coordination compounds, and the fundamental role of d-electrons in bonding.
第一行d区元素包括从钪到锌的十个金属，是过渡金属化学的基石。随着3d亚层在这一周期中逐步填充，出现了一系列引人注目的性质：可变的氧化态、水溶液中的鲜艳颜色、顺磁性、广泛的催化行为以及形成稳定配离子的能力。在IB化学高级水平中，对这些元素的深入探究可以揭示电子构型的微妙之处、配位化合物的立体异构现象以及d电子在成键中的核心作用。
1. Scope and Definition of the First-Row d-Block | 第一行d区的范围与定义
ms, the 3d orbital set is being filled according to the Aufbau principle, although there are notable exceptions due to the stability of half-filled and fully filled d-sublevels. It is essential to distinguish between a d-block element and a transition element: according to the IUPAC definition, a transition element is one whose atom has a partially filled d-sublevel, or which can give rise to cations with an incomplete d-sublevel.
第一行d区元素是原子序数从21的钪到30的锌的十种金属元素。在这些原子中，3d轨道按照构造原理被填充，但由于半充满和全充满d亚层的稳定性，存在一些显著的例外。必须区分d区元素和过渡元素：根据IUPAC的定义，过渡元素是指原子具有部分填充的d亚层，或者可以形成含有未充满d亚层的阳离子的元素。
Applying this definition, scandium and zinc are often not classified as transition metals. Scandium's only common ion, Sc³⁺, has an [Ar] electron configuration with an empty 3d-sublevel, while zinc in its sole oxidation state Zn²⁺ has the configuration [Ar]3d¹⁰, giving it a completely filled d-sublevel. Nevertheless, both are d-block elements and are usually included in discussions of first-row chemistry to illustrate important trends.
应用此定义，钪和锌通常不被归类为过渡金属。钪唯一常见的离子Sc³⁺具有[Ar]电子构型，3d亚层为空，而锌在其唯一的氧化态Zn²⁺中的构型为[Ar]3d¹⁰，使其d亚层完全填满。尽管如此，它们仍属于d区元素，并常被纳入第一行化学的讨论中以说明重要趋势。
2. Electron Configurations from Scandium to Zinc | 从钪到锌的电子构型
The ground-state electron configurations of the first-row d-block atoms reveal the competition between the 4s and 3d orbitals. Potassium and calcium precede the series with [Ar]4s¹ and [Ar]4s², respectively, and then the 3d orbitals begin to fill. The expected configuration for scandium is [Ar]3d¹4s², and this pattern of adding one 3d electron holds for the next elements with two critical exceptions.
第一行d区原子的基态电子构型揭示了4s和3d轨道之间的竞争。钾和钙分别以[Ar]4s¹和[Ar]4s²的构型先于该系列，随后3d轨道开始填充。钪的预期构型为[Ar]3d¹4s²，这种增加一个3d电子的模式对接下来的元素也成立，但有两个关键的例外。
| Element | Symbol | Atomic Number | Electron Configuration |
|---|---|---|---|
| Scandium | Sc | 21 | [Ar]3d¹4s² |
| Titanium | Ti | 22 | [Ar]3d²4s² |
| Vanadium | V | 23 | [Ar]3d³4s² |
| Chromium | Cr | 24 | [Ar]3d⁵4s¹ |
| Manganese | Mn | 25 | [Ar]3d⁵4s² |
| Iron | Fe | 26 | [Ar]3d⁶4s² |
| Cobalt | Co | 27 | [Ar]3d⁷4s² |
| Nickel | Ni | 28 | [Ar]3d⁸4s² |
| Copper | Cu | 29 | [Ar]3d¹⁰4s¹ |
| Zinc | Zn | 30 | [Ar]3d¹⁰4s² |
Chromium adopts [Ar]3d⁵4s¹ instead of the expected 3d⁴4s² because a half-filled 3d-sublevel imparts extra stability. Similarly, copper takes [Ar]3d¹⁰4s¹ rather than 3d⁹4s², gaining the stability of a fully filled 3d-sublevel. These anomalies are rationalised by the small energy gap between 3d and 4s orbitals and the exchange energy associated with parallel electron spins.
铬采用[Ar]3d⁵4s¹而不是预期的3d⁴4s²，因为半充满的3d亚层带来了额外的稳定性。同样，铜采用[Ar]3d¹⁰4s¹而不是3d⁹4s²，获得了全充满3d亚层的稳定性。这些异常现象可以通过3d和4s轨道之间较小的能隙以及与平行电子自旋相关的交换能来合理解释。
3. Defining a Transition Element: The d-Sublevel Criterion | 过渡元素的定义：d亚层判据
The strict IUPAC definition excludes scandium and zinc from the transition series. Sc³⁺ has the electron configuration [Ar], with all 3d-orbitals vacant, while Zn²⁺ possesses [Ar]3d¹⁰, a completely filled d-sublevel. Neither common ion can exhibit d-d transitions, which are responsible for colour and many other characteristic properties. Therefore, when discussing true transition metal behaviour, the focus is on titanium through copper.
严格的IUPAC定义将钪和锌排除在过渡系列之外。Sc³⁺的电子构型为[Ar]，所有3d轨道均为空，而Zn²⁺具有[Ar]3d¹⁰，即完全填满的d亚层。这两种常见离子都不能表现d-d跃迁，而d-d跃迁是颜色和许多其他特征性质的来源。因此，在讨论真正的过渡金属行为时，重点是钛到铜。
This distinction is assessed in IB examinations. Candidates must be able to explain why Zn²⁺ compounds are colourless and why Sc shows almost exclusively a +3 oxidation state with no d-electrons available for bonding. The partially filled d-sublevel is the key to variable oxidation states, catalytic activity, and magnetic behaviour.
这一区别在IB考试中有所考查。考生必须能够解释为何Zn²⁺化合物无色，以及为何Sc几乎只表现出+3氧化态且没有可用的d电子用于成键。部分填充的d亚层是可变氧化态、催化活性和磁学行为的关键。
4. Variable Oxidation States of First-Row Metals | 第一行金属的可变氧化态
One of the most striking features of transition elements is their ability to exist in multiple oxidation states. The availability of closely spaced 3d and 4s electrons allows successive ionisation energies to increase gradually, so several electrons can be removed without an insurmountable energy barrier. Scandium and zinc are limited to +3 and +2 respectively, but the central metals display a rich redox chemistry.
过渡元素最显著的特征之一是它们能以多种氧化态存在。紧密排布的3d和4s电子的存在使得连续电离能逐步增加，因此可以在没有不可逾越的能垒下移走若干个电子。钪和锌分别局限于+3和+2氧化态，但中间金属展现出丰富的氧化还原化学。
For example, vanadium shows +2, +3, +4 and +5 states, each with characteristic colours in solution: V²⁺ is violet, V³⁺ is green, VO²⁺ is blue, and VO₂⁺ is yellow. Manganese spans +2 (pale pink) to +7 (in MnO₄⁻, intense purple), while iron's +2 and +3 states underpin biological oxygen carriers and industrial redox processes. The relative stabilities of these states are influenced by pH, ligand environment, and the presence of oxidising or reducing agents.
例如，钒表现出+2、+3、+4和+5氧化态，每种在溶液中都有特征颜色：V²⁺为紫色，V³⁺为绿色，VO²⁺为蓝色，VO₂⁺为黄色。锰的氧化态范围从+2（浅粉色）到+7（MnO₄⁻，深紫色），而铁的+2和+3态支撑着生物载氧体和工业氧化还原过程。这些氧化态的相对稳定性受pH、配体环境以及氧化剂或还原剂存在的影响。
5. Formation of Coloured Ions and d-d Transitions | 有色离子的形成与d-d跃迁
Colour in first-row d-block compounds arises mainly from electronic transitions within partially filled d-orbitals, known as d-d transitions. In an isolated atom, the five d-orbitals are degenerate, but when a metal ion is surrounded by ligands in a complex, the electrostatic field splits the d-orbitals into two sets with an energy gap Δ (often called crystal field splitting). Visible light of appropriate wavelength can be absorbed to promote an electron from a lower-energy d-orbital to a higher one, and the transmitted light is complementary to the absorbed colour.
第一行d区化合物的颜色主要来源于部分填充的d轨道内的电子跃迁，称为d-d跃迁。在孤立原子中，五个d轨道是简并的，但当金属离子被配体包围在配合物中时，静电场将d轨道分裂成两组，产生能隙Δ（通常称为晶体场分裂）。适当波长的可见光可被吸收，将电子从较低能量的d轨道激发到较高能量的d轨道，透射光的颜色与吸收光互补。
For example, [Cu(H₂O)₆]²⁺ appears blue because it absorbs mainly orange-red light, while [Fe(H₂O)₆]²⁺ is pale green. Ions with a d⁰ configuration (Sc³⁺, Ti⁴⁺) or d¹⁰ configuration (Zn²⁺, Cu⁺) cannot undergo d-d transitions and appear colourless. The nature of the ligand also affects the size of Δ, giving rise to the spectrochemical series which is explored in the context of ligand strength.
例如，[Cu(H₂O)₆]²⁺呈蓝色，因为它主要吸收橙红色光，而[Fe(H₂O)₆]²⁺为浅绿色。具有d⁰构型（Sc³⁺、Ti⁴⁺）或d¹⁰构型（Zn²⁺、Cu⁺）的离子无法发生d-d跃迁而呈无色。配体的性质也会影响Δ的大小，由此产生光谱化学序列，可在配体强度的背景下进行探讨。
6. Magnetic Properties: Paramagnetism and Unpaired Electrons | 磁学性质：顺磁性与未成对电子
The magnetic behaviour of a first-row transition metal ion is determined almost entirely by the number of unpaired d-electrons. Species with one or more unpaired electrons are paramagnetic and are attracted to an external magnetic field; the greater the number of unpaired spins, the stronger the paramagnetic effect. Ions with all electrons paired are diamagnetic and are weakly repelled.
第一行过渡金属离子的磁学行为几乎完全由未成对d电子的数目决定。具有一个或多个未成对电子的物种是顺磁性的，会被外加磁场吸引；未成对自旋数越多，顺磁效应越强。所有电子均配对的离子是抗磁性的，会受到微弱排斥。
For instance, Fe²⁺ in a high-spin octahedral complex with four unpaired electrons is strongly paramagnetic, while [Fe(CN)₆]⁴⁻ in a low-spin arrangement with all electrons paired is diamagnetic. Mn²⁺ (d⁵) typically has five unpaired electrons, showing a high magnetic moment. The measurement of magnetic moments provides experimental evidence for electron configurations and bonding models in coordination compounds.
例如，Fe²⁺在具有四个未成对电子的高自旋八面体配合物中表现出强顺磁性，而[Fe(CN)₆]⁴⁻在低自旋构型下所有电子均配对，为抗磁性。Mn²⁺（d⁵）通常有五个未成对电子，显示出高磁矩。磁矩的测定为配位化合物中的电子构型和成键模型提供了实验证据。
7. Catalytic Activity of Transition Metals and Their Compounds | 过渡金属及其化合物的催化活性
Many first-row d-block elements and their compounds act as heterogeneous or homogeneous catalysts. Their effectiveness stems from the ability to adopt multiple oxidation states, providing alternative reaction pathways with lower activation energy, and from the availability of partially filled d-orbitals that can form temporary bonds with reactant molecules.
许多第一行d区元素及其化合物充当多相或均相催化剂。它们的有效性源于能够采取多种氧化态，从而提供活化能较低的替代反应路径，以及有部分填充的d轨道可用，可以与反应物分子形成暂时键合。
Iron is used as a heterogeneous catalyst in the Haber process for ammonia synthesis, while vanadium(V) oxide catalyses the Contact process for sulfuric acid production through a redox cycle involving V(+5) and V(+4). Nickel serves as a hydrogenation catalyst for vegetable oils, and manganese dioxide catalyses the decomposition of hydrogen peroxide. In homogeneous catalysis, aqueous Fe²⁺ or Fe³⁺ ions catalyse the oxidation of iodide ions by peroxodisulfate, illustrating the classic role of a redox catalyst.
铁在哈伯法氨合成中作为多相催化剂，五氧化二钒通过涉及V(+5)和V(+4)的氧化还原循环催化接触法生产硫酸。镍用作植物油加氢催化剂，二氧化锰催化过氧化氢分解。在均相催化中，水溶液中的Fe²⁺或Fe³⁺离子催化过二硫酸根离子氧化碘离子的反应，展示了氧化还原催化剂的经典作用。
8. Complex Ions: Ligands, Coordination Number, and Geometry | 配离子：配体、配位数与几何构型
A complex ion consists of a central metal atom or ion bonded to a surrounding array of molecules or ions called ligands. The bond is a coordinate (dative covalent) bond in which the ligand donates a lone pair of electrons into an empty orbital of the metal. The number of ligand atoms directly bonded to the metal centre is the coordination number, which commonly ranges from 2 to 6 for first-row d-block metals.
配离子由一个中心金属原子或离子与周围称为配体的分子或离子阵列键合而成。这种键是配位（给予共价）键，配体将孤对电子赠予金属的空轨道。直接与金属中心键合的配体原子数目是配位数，对第一行d区金属而言通常为2到6。
Typical ligands include water (aqua), ammonia (ammine), cyanide (cyano), chloride (chloro) and hydroxide (hydroxo). Ligands can be neutral or anionic, and the overall charge of the complex is the sum of the oxidation state of the metal and the charges of the ligands. For instance, [Fe(H₂O)₆]³⁺ is a hexaaquairon(III) ion, while [CuCl₄]²⁻ is a tetrachlorocuprate(II) ion.
典型的配体包括水（aquo）、氨（ammine）、氰根（cyano）、氯离子（chloro）和氢氧根（hydroxo）。配体可以是中性或阴离子的，配合物的总电荷是金属氧化态和配体电荷的总和。例如，[Fe(H₂O)₆]³⁺是六水合铁(III)离子，而[CuCl₄]²⁻是四氯合铜(II)离子。
9. Common Ligands and Chelation | 常见配体与螯合作用
Ligands are classified by the number of donor atoms they possess. Monodentate ligands, such as H₂O:, :NH₃ and Cl⁻, bind through a single atom. Bidentate ligands, like 1,2-diaminoethane (en) and the ethanedioate ion (C₂O₄²⁻), can use two donor atoms to form a chelate ring. Polydentate ligands such as EDTA⁴⁻ can bind with six donor atoms, forming very stable complexes.
配体按其拥有的供体原子数量分类。单齿配体，如H₂O:、:NH₃和Cl⁻，通过单个原子结合。双齿配体，如1,2-二氨基乙烷（en）和乙二酸根离子（C₂O₄²⁻），可以使用两个供体原子形成螯合环。多齿配体如EDTA⁴⁻可以用六个供体原子结合，形成非常稳定的配合物。
The chelate effect describes the enhanced thermodynamic stability of a complex containing chelate rings compared with an analogous system with monodentate ligands. [Ni(en)₃]²⁺ is far more stable than [Ni(NH₃)₆]²⁺ due to the favourable entropy change when multiple chelate rings are formed. This principle is exploited in analytical chemistry and in medical treatments for heavy metal poisoning.
螯合效应描述了含有螯合环的配合物相对于含单齿配体的类似体系具有更高的热力学稳定性。[Ni(en)₃]²⁺比[Ni(NH₃)₆]²⁺稳定得多，这是由于形成多个螯合环时有利的熵变。这一原理在分析化学和重金属中毒的医学治疗中得到应用。
10. Shapes of Complex Ions: Octahedral, Tetrahedral, and Square Planar | 配离子的形状：八面体、四面体和平面正方形
The shape of a complex ion is determined primarily by its coordination number and the electronic configuration of the metal centre. Six-coordinate complexes are almost invariably octahedral, as seen in [Fe(CN)₆]³⁻ and [Co(NH₃)₆]³⁺. Four-coordinate complexes can adopt either a tetrahedral geometry, common for nonpolar ions with sterically large ligands, or a square planar geometry, favoured by d⁸ metal ions such as Ni(II), Pd(II), and Pt(II).
配离子的形状主要由其配位数和金属中心的电子构型决定。六配位配合物几乎总是八面体形状，如[Fe(CN)₆]³⁻和[Co(NH₃)₆]³⁺。四配位配合物可以采取四面体几何构型，常见于具有较大空间位阻配体的非极性离子，或采取平面正方形几何构型，后者有利于d⁸金属离子如Ni(II)、Pd(II)和Pt(II)。
Tetrahedral complexes, such as [CoCl₄]²⁻, arise because the ligand-field stabilisation energy often favours octahedral coordination for most d-electronic counts, but in some cases the sterics and lack of strong field ligands yield tetrahedral structures. Square planar complexes like [Ni(CN)₄]²⁻ and the well-known anticancer drug cisplatin, [PtCl₂(NH₃)₂], result from the high splitting of the d(x²-y²) orbital, which makes it energetically unfavourable to populate this orbital, leaving four ligands in a plane.
四面体配合物，如[CoCl₄]²⁻，其形成是因为对大多数d电子数而言八面体配位常占优势，但在某些情况下，位阻效应和缺乏强场配体可导致四面体结构。平面正方形配合物，如[Ni(CN)₄]²⁻和著名的抗癌药顺铂[PtCl₂(NH₃)₂]，是d(x²-y²)轨道高分裂的结果，这使得该轨道被占据在能量上不利，从而留下四个配体处于一个平面内。
11. Isomerism in Complex Ions (HL) | 配离子的异构现象（HL）
Isomerism in coordination compounds is a core Higher Level topic. Two broad categories are structural isomerism, where the connectivity of atoms differs, and stereoisomerism, where the connectivity is the same but the spatial arrangement differs. Structural isomers include ionisation isomers (exchange of ions inside and outside the coordination sphere), hydrate isomers (water acting as
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