📚 Transition Elements: Definition and Characteristics | 过渡元素：定义与特征
Transition elements, also known as transition metals, are a group of elements in the d-block of the periodic table that have partially filled d-orbitals either in their atoms or in their common oxidation states. They exhibit characteristic properties such as variable oxidation states, coloured compounds, complex formation, catalytic activity and magnetic behaviour. This article provides a detailed explanation of the definition and key characteristics of transition elements as required by the CIE A-Level Chemistry syllabus.
过渡元素亦称过渡金属，是周期表中d区的一组元素，其原子或常见氧化态离子具有部分填充的d轨道。它们表现出可变氧化态、有色化合物、形成配合物、催化活性及磁性等特征性质。本文按照CIE A-Level化学考纲，详细阐述过渡元素的定义与主要特征。
1. What is a Transition Element? | 什么是过渡元素？
According to the CIE specification, a transition element is a metal that can form one or more stable ions with a partially filled d subshell. This definition focuses on ionic species rather than just the neutral atom. For example, iron forms Fe²⁺ and Fe³⁺ ions: Fe²⁺ has the electronic configuration [Ar] 3d⁶ and Fe³⁺ has [Ar] 3d⁵. Both ions have partially filled 3d orbitals, so iron is a genuine transition element.
按照CIE考纲的定义，过渡元素是能够形成一个或多个具有部分填充d亚层的稳定离子的金属。该定义侧重于离子而非仅指中性原子。例如，铁可形成Fe²⁺和Fe³⁺离子：Fe²⁺的电子构型为[Ar] 3d⁶，Fe³⁺的电子构型为[Ar] 3d⁵，两者的3d轨道均部分填充，因此铁是真正的过渡元素。
It is important to distinguish between d-block elements and transition elements. A d-block element is any element whose highest-energy electrons are in a d subshell. However, zinc has the configuration [Ar] 3d¹⁰ 4s² and commonly forms Zn²⁺ ([Ar] 3d¹⁰), which has a completely filled d subshell. Hence zinc is a d-block element but not a transition element. Similarly, scandium forms Sc³⁺ with [Ar] 3d⁰, so it also lies outside the transition element category.
必须区分d区元素与过渡元素。d区元素是指最高能量电子位于d亚层的任何元素。然而，锌的构型为[Ar] 3d¹⁰ 4s²，常见Zn²⁺为[Ar] 3d¹⁰，其d亚层完全填满，所以锌是d区元素而非过渡元素。同样，钪形成Sc³⁺，构型为[Ar] 3d⁰，因此也不属于过渡元素。
2. Electronic Configuration | 电子构型
The general electronic configuration of transition elements is (n-1)d¹⁻¹⁰ ns¹⁻². The (n-1)d and ns energy levels are very close in energy, which explains many of their characteristic properties. For example, chromium has the configuration [Ar] 3d⁵ 4s¹ instead of the expected [Ar] 3d⁴ 4s². This anomaly arises because a half-filled 3d subshell is extra stable due to reduced electron-electron repulsion and exchange energy. Copper similarly adopts [Ar] 3d¹⁰ 4s¹ instead of [Ar] 3d⁹ 4s² because a completely filled d subshell is particularly stable.
过渡元素的通式为 (n-1)d¹⁻¹⁰ ns¹⁻²。(n-1)d与ns能级非常接近，这解释了许多特征性质。例如，铬的构型为[Ar] 3d⁵ 4s¹，而非预期的[Ar] 3d⁴ 4s²。这种异常源于半充满的3d亚层因电子排斥减少和交换能而额外稳定。铜同样取[Ar] 3d¹⁰ 4s¹而非[Ar] 3d⁹ 4s²，因为全充满的d亚层特别稳定。
When transition metals form positive ions, the 4s electrons are lost before the 3d electrons. For instance, iron loses two 4s electrons to form Fe²⁺: [Ar] 3d⁶, and then loses one 3d electron to form Fe³⁺: [Ar] 3d⁵. This order is the opposite of what might be expected from filling order and must be remembered carefully in A-Level chemistry.
过渡金属形成正离子时，先失去4s电子，再失去3d电子。例如，铁先失去两个4s电子生成Fe²⁺：[Ar] 3d⁶，再失去一个3d电子生成Fe³⁺：[Ar] 3d⁵。这一顺序与通常的填充顺序相反，在A-Level化学中需要特别牢记。
3. Variable Oxidation States | 可变氧化态
One of the most distinctive features of transition elements is their ability to exhibit more than one oxidation state in compounds. This arises because the energy difference between the 3d and 4s orbitals is small, so a variable number of electrons can be involved in bonding. For example, iron shows +2 and +3; copper shows +1 and +2; manganese shows +2, +4, +6 and +7; vanadium shows +2, +3, +4 and +5.
过渡元素最显著的特征之一是能在化合物中呈现多种氧化态。这是因为3d与4s轨道间的能量差很小，参与成键的电子数可以变化。例如，铁显示+2和+3；铜显示+1和+2；锰显示+2、+4、+6和+7；钒显示+2、+3、+4和+5。
The highest oxidation state of a transition element often equals the total number of electrons in the 4s and 3d subshells. Thus manganese (with 4s² 3d⁵) reaches +7, and vanadium (with 4s² 3d³) reaches +5. In lower oxidation states, the ions are typically simple cations; in higher oxidation states, the element is often present in covalent compounds or oxyanions, such as MnO₄⁻ or VO₃⁻.
过渡元素的最高氧化态通常等于4s和3d亚层的电子总数。因此，锰（4s² 3d⁵）可达到+7，钒（4s² 3d³）可达到+5。在较低氧化态时，离子通常为简单阳离子；在较高氧化态时，元素常存在于共价化合物或含氧酸根中，如MnO₄⁻或VO₃⁻。
4. Formation of Complex Ions | 形成配合离子
Transition metal ions have a high charge density and small size, and they possess vacant d orbitals that can accept lone pairs from ligands. A complex ion consists of a central metal ion surrounded by ligands, which are molecules or anions that donate a lone pair of electrons through dative coordinate bonds. For example, the hexaaquairon(III) ion, [Fe(H₂O)₆]³⁺, has six water molecules coordinated to the central Fe³⁺ ion in an octahedral arrangement.
过渡金属离子电荷密度高、体积小，并具有可接受配体孤对电子的空d轨道。配合离子由中心金属离子与周围配体组成，配体是通过配位键提供孤对电子的分子或阴离子。例如，六水合铁(III)离子[Fe(H₂O)₆]³⁺中，六个水分子以八面体构型配位在中心Fe³⁺周围。
Common ligands include water (H₂O), ammonia (NH₃), chloride ions (Cl⁻) and cyanide ions (CN⁻). The coordination number is the total number of coordinate bonds formed by the central metal ion. Most transition metal complexes have a coordination number of six in an octahedral geometry, but some have four in a tetrahedral or square planar geometry, such as [CuCl₄]²⁻ and [Pt(NH₃)₂Cl₂].
常见配体包括水（H₂O）、氨（NH₃）、氯离子（Cl⁻）和氰离子（CN⁻）。配位数是中心金属离子形成的配位键总数。大多数过渡金属配合物的配位数为六，呈八面体几何构型；也有一些为四配位，如[CuCl₄]²⁻呈四面体，[Pt(NH₃)₂Cl₂]呈平面正方形。
5. Coloured Compounds | 有色化合物
Transition metal ions and their complexes are often coloured because electrons in the partially filled d orbitals can absorb visible light and be promoted to a higher-energy d orbital. The d orbitals split into two sets of different energies in the presence of ligands. This splitting is known as crystal field splitting. When light passes through the compound, certain wavelengths are absorbed to cause d-d transitions; the remaining transmitted light appears as the complementary colour.
过渡金属离子及其配合物通常具有颜色，因为部分填充的d轨道中的电子能吸收可见光，跃迁到更高能量的d轨道。在配体存在下，d轨道分裂为两组能量不同的轨道，即晶体场分裂。当光穿过化合物时，某些波长的光被吸收以引发d-d跃迁；剩余透射光呈现补色。
The exact colour depends on the metal ion, its oxidation state, the nature of the ligand and the coordination geometry. For example, [Ti(H₂O)₆]³⁺ absorbs green-yellow light and appears purple; [Cu(H₂O)₆]²⁺ absorbs orange-red light and appears blue. A table of common hydrated transition metal ions is shown below:
具体颜色取决于金属离子、氧化态、配体种类和配位几何。例如，[Ti(H₂O)₆]³⁺吸收黄绿光而呈紫色；[Cu(H₂O)₆]²⁺吸收橙红光而呈蓝色。下表列出常见水合过渡金属离子的颜色：
| Ion | 离子 | Colour | 颜色 |
|---|---|
| [Ti(H₂O)₆]³⁺ | Purple | 紫色 |
| [V(H₂O)₆]²⁺ | Violet | 紫罗兰色 |
| [V(H₂O)₆]³⁺ | Green | 绿色 |
| [Cr(H₂O)₆]³⁺ | Green | 绿色 |
| [Fe(H₂O)₆]²⁺ | Pale green | 浅绿色 |
| [Fe(H₂O)₆]³⁺ | Yellow-brown | 黄棕色 |
| [Cu(H₂O)₆]²⁺ | Blue | 蓝色 |
6. Catalytic Activity | 催化作用
Transition metals and their compounds are excellent catalysts because of their ability to adopt variable oxidation states. A catalyst can provide an alternative reaction pathway with a lower activation energy by temporarily changing oxidation state and then returning to its original state. This is essential in many industrial processes.
过渡金属及其化合物是优良的催化剂，因为它们能呈现可变氧化态。催化剂可通过暂时改变氧化态并随后恢复原状，提供一条具有较低活化能的新反应途径。这在许多工业过程中至关重要。
Heterogeneous catalysis occurs when the catalyst is in a different phase from the reactants. For example, iron is used in the Haber process to produce ammonia, and vanadium(V) oxide, V₂O₅, is used in the Contact process to manufacture sulfuric acid. In the Contact process, V₂O₅ is reduced to V₂O₄ and then re-oxidised by oxygen. Homogeneous catalysis occurs when the catalyst and reactants are in the same phase; transition metal ions in solution can catalyse redox reactions, such as Fe²⁺/Fe³⁺ in the reaction between iodide and persulfate ions.
多相催化指催化剂与反应物处于不同相态。例如，铁用于哈伯法合成氨，五氧化二钒V₂O₅用于接触法制备硫酸。在接触法中，V₂O₅先被还原为V₂O₄，再被氧气重新氧化。均相催化指催化剂与反应物处于同一相态；溶液中的过渡金属离子可催化氧化还原反应，例如Fe²⁺/Fe³⁺催化碘离子与过硫酸根离子的反应。
7. Magnetic Properties | 磁性
The magnetic behaviour of transition elements arises from the presence of unpaired electrons in the d orbitals. A substance is paramagnetic if it contains unpaired electrons and is attracted by an external magnetic field. A substance is diamagnetic if all electrons are paired and is weakly repelled by a magnetic field. The greater the number of unpaired electrons, the stronger the paramagnetic effect.
过渡元素的磁性源于d轨道中的未成对电子。含有未成对电子的物质为顺磁性，会被外磁场吸引；若所有电子均成对则为抗磁性，会受到磁场微弱排斥。未成对电子越多，顺磁性越强。
For example, Zn²⁺ has the configuration [Ar] 3d¹⁰ with no unpaired electrons, so zinc compounds are diamagnetic. In contrast, Fe³⁺ has [Ar] 3d⁵ with five unpaired electrons, making its compounds strongly paramagnetic. In the solid state, the elements iron, cobalt and nickel exhibit ferromagnetism, which enables them to be magnetised permanently. This property is widely used in magnetic materials and data storage.
例如，Zn²⁺构型为[Ar] 3d¹⁰，没有未成对电子，因此锌化合物为抗磁性。相比之下，Fe³⁺的[Ar] 3d⁵有五个未成对电子，其化合物呈强顺磁性。在固态下，铁、钴、镍三种元素呈现铁磁性，能永久磁化。该性质广泛用于磁性材料和数据存储。
8. Other Physical Characteristics | 其他物理特征
Transition elements have high melting points, high densities and high tensile strength compared with s-block metals. This is because the d electrons contribute to metallic bonding in addition to the delocalised s electrons, increasing the strength of metallic bonds. For example, iron melts at 1538 °C, whereas sodium melts at only 98 °C. The strong metallic bonding also results in high electrical conductivity.
与s区金属相比，过渡元素具有高熔点、高密度和高抗拉强度。这是因为除离域s电子外，d电子也参与金属键的形成，增强了金属键强度。例如，铁的熔点为1538 °C，而钠的熔点仅为98 °C。强金属键也带来良好的导电性。
Many transition metals form alloys with varying compositions that have desirable properties, such as stainless steel (iron with chromium and nickel). These alloys are harder and more resistant to corrosion than the pure metals. This feature is exploited in structural materials, catalysis and electrical wiring.
许多过渡金属可形成不同组成的合金，具有理想性能，例如不锈钢（铁与铬、镍的合金）。合金比纯金属更硬、更耐腐蚀。这一特性被广泛应用于结构材料、催化和电线等领域。
9. Why Zinc and Scandium Are Not Transition Elements | 锌和钪为什么不是过渡元素
A common examination question asks why zinc and scandium are excluded from the transition elements. Zinc has the electronic configuration [Ar] 3d¹⁰ 4s². Its only common oxidation state is +2, corresponding to Zn²⁺ with [Ar] 3d¹⁰, which has a completely filled d subshell. Therefore, zinc does not meet the definition because its ions do not have a partially filled d subshell.
一个常见考题是问锌和钪为何不属于过渡元素。锌的电子构型为[Ar] 3d¹⁰ 4s²，其常见氧化态只有+2，对应Zn²⁺的[Ar] 3d¹⁰，d亚层完全填满。因此，锌不符合定义，因为其离子没有部分填充的d亚层。
Scandium has the configuration [Ar] 3d¹ 4s², but its only stable ion is Sc³⁺ with [Ar] 3d⁰, which has an empty d subshell. Because Sc³⁺ has no d electrons, it does not show characteristic transition metal behaviour such as coloured compounds or variable oxidation states. Thus scandium is classified as a d-block element but not a transition element. This exception is essential to remember when classifying elements.
钪的构型为[Ar] 3d¹ 4s²，但其唯一稳定离子是Sc³⁺，构型为[Ar] 3d⁰，d亚层为空。由于Sc³⁺没有d电子，所以不表现出有色化合物、可变氧化态等过渡金属特性。因此钪属于d区元素，但不是过渡元素。分类时记住这一例外非常重要。
10. Summary of Key Features | 关键特征总结
In summary, transition elements are defined by the presence of a partially filled d subshell in at least one stable ion. Their characteristic properties include variable oxidation states, complex ion formation, coloured compounds, catalytic activity and magnetic behaviour. These properties are explained by the availability of partially filled d orbitals and the small energy gap between the 3d and 4s subshells.
总之，过渡元素以至少一种稳定离子具有部分填充d亚层为定义。其典型特征包括可变氧化态、形成配合离子、有色化合物、催化活性和磁性。这些性质可由部分填充的d轨道以及3d与4s亚层之间较小的能隙来解释。
Remember that d-block elements such as zinc and scandium are excluded because their ions have either a full or an empty d subshell. A clear understanding of this definition and the related properties is essential for answering exam questions on the chemistry of transition elements.
请记住，锌和钪等d区元素因离子d亚层全满或全空而被排除在过渡元素之外。清晰理解这一定义及相关性质，对于回答过渡元素化学考题至关重要。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导