Transition Elements | 过渡元素

📚 Transition Elements | 过渡元素

Transition elements are a central topic in A-Level Chemistry because they connect atomic structure, bonding, redox, colour and catalysis. This article follows the Cambridge International A-Level specification and covers the definition of a transition element, electron configurations, complex ions, colour, variable oxidation states and catalytic behaviour. Work through each section carefully and use the examples to support your written answers.

过渡元素是 A-Level 化学的核心主题，因为它将原子结构、化学键、氧化还原、颜色和催化作用联系在一起。本文依据剑桥国际 A-Level 大纲，涵盖过渡元素的定义、电子构型、配离子、颜色、可变氧化态和催化行为。请认真学习每一节，并利用这些例子来支撑你的书面作答。

1. Definition of a Transition Element | 过渡元素的定义

A transition element is defined as a d-block element that forms at least one stable ion with an incomplete d subshell. This definition is important because it excludes scandium and zinc. Scandium forms only the Sc³⁺ ion with the electron configuration [Ar] 3d⁰, and zinc forms only Zn²⁺ with [Ar] 3d¹⁰. Since neither Sc³⁺ nor Zn²⁺ has a partially filled d subshell, scandium and zinc are d-block elements but not transition elements. In contrast, copper is a transition element because Cu²⁺ has the configuration [Ar] 3d⁹.

过渡元素是指能形成至少一种稳定离子且该离子具有未充满 d 亚层的 d 区元素。这一定义非常重要，因为它把钪和锌排除在外。钪只形成 Sc³⁺ 离子，电子构型为 [Ar] 3d⁰；锌只形成 Zn²⁺，电子构型为 [Ar] 3d¹⁰。由于 Sc³⁺ 和 Zn²⁺ 都不具有部分填充的 d 亚层，因此钪和锌属于 d 区元素，但不属于过渡元素。相反，铜是过渡元素，因为 Cu²⁺ 的构型为 [Ar] 3d⁹。

2. Electron Configurations of the 3d Series | 3d 系列元素的电子构型

The first transition series runs from scandium to zinc. In neutral atoms, the 4s subshell fills before the 3d subshell, but when transition metals form positive ions, the 4s electrons are removed first. Chromium and copper show anomalous configurations: chromium is [Ar] 3d⁵ 4s¹ and copper is [Ar] 3d¹⁰ 4s¹. This is because a half-filled 3d subshell in chromium and a fully filled 3d subshell in copper give extra stability.

第一过渡系从钪到锌。在中性原子中，4s 亚层先于 3d 亚层填充，但当过渡金属形成正离子时，4s 电子首先失去。铬和铜表现出反常的电子构型：铬是 [Ar] 3d⁵ 4s¹，铜是 [Ar] 3d¹⁰ 4s¹。这是因为铬的半充满 3d 亚层和铜的全充满 3d 亚层具有额外的稳定性。

The table below summarises the electron configurations of the first transition series.

下表总结了第一过渡系的电子构型。

3. Physical Properties and Metallic Character | 物理性质与金属特性

Transition metals are typical metals with high melting points, high boiling points, high densities and good electrical and thermal conductivity. These properties arise from strong metallic bonding involving delocalised electrons from both the 4s and 3d orbitals. However, these physical properties are not unique to transition metals, so the characteristic chemical properties such as variable oxidation states and complex formation are more useful for identification.

过渡金属是典型的金属，具有高熔点、高沸点、高密度以及良好的导电性和导热性。这些性质来源于涉及 4s 和 3d 轨道离域电子的强金属键。然而，这些物理性质并不是过渡元素独有的，因此可变氧化态和形成配合物等特征化学性质更常用于鉴别。

4. Variable Oxidation States | 可变的氧化态

Transition elements show variable oxidation states because the energy difference between the 3d and 4s electrons is small, allowing different numbers of electrons to be lost in chemical reactions. The relative stability of common oxidation states changes across the period. For example, iron shows +2 and +3, manganese shows +2, +4,

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