Electron Configuration Revision for IB & CCEA Chemistry | IB CCEA 化学：电子排布 考点精讲

📚 Electron Configuration Revision for IB & CCEA Chemistry | IB CCEA 化学：电子排布 考点精讲

Mastering electron configuration is a fundamental skill for any IB or CCEA Chemistry student. The arrangement of electrons in atoms dictates chemical reactivity, bonding behaviour and the structure of the periodic table itself. This topic connects quantum mechanics to observable periodic trends and is essential for explaining why elements behave the way they do. This article provides a complete, exam-focused walkthrough of the principles, notation and exceptions you need to know, with all concepts explained clearly in both English and Chinese to support bilingual learners.

掌握电子排布是每一位 IB 或 CCEA 化学学生的基本功。原子中电子的排列方式决定了化学反应活性、成键行为以及周期表本身的结构。这一主题将量子力学与可观察的周期递变规律联系在一起，对于解释元素为何表现出特定的性质至关重要。本文为备考学生提供一份完整、紧扣考点的讲解，涵盖原理、书写方式和特殊例外，并以中英双语逐点对照，帮助双语学习者透彻理解。

1. Introduction to Electron Configuration | 电子排布简介

Electron configuration describes how electrons are distributed among the orbitals of an atom. It provides a ‘map’ of where electrons are likely to be found, using principles of quantum theory. Knowing the electron configuration allows chemists to predict an element’s valency, ion formation and magnetic properties.

电子排布描述了电子在原子轨道中的分布情况。它利用量子理论原理，提供了一张电子可能出现位置的“地图”。掌握电子排布能帮助化学家预测元素的化合价、离子形成方式以及磁性行为。

The configuration is based on four quantum numbers and three key rules: the Aufbau principle, Hund’s rule and the Pauli exclusion principle. In IB and CCEA examinations, you will be required to write configurations for atoms and ions up to Z = 36 (krypton) and beyond, as well as to rationalise exceptions such as chromium and copper.

电子排布建立在四个量子数和三个关键规则之上：构造原理、洪特规则和泡利不相容原理。在 IB 和 CCEA 考试中，你需要能够书写原子序数 Z = 36（氪）及更高元素的原子和离子的电子排布，并能解释铬和铜等特殊例外。

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2. Quantum Numbers | 量子数

Each electron in an atom is described by a set of four quantum numbers. These numbers define the electron’s energy, orbital shape, orientation and spin. They arise from the solutions to the Schrödinger equation and are strictly governed by mathematical constraints.

原子中的每一个电子都由一组四个量子数来描述。这些量子数定义了电子的能量、轨道形状、取向和自旋。它们源自薛定谔方程的解，并受到严格的数学约束。

Quantum Number | 量子数	Symbol | 符号	Allowed Values | 允许取值	Specifies | 指明
Principal | 主量子数	n	1, 2, 3, …	Energy level / shell | 能级 / 电子层
Azimuthal | 角量子数	ℓ	0 to (n – 1)	Subshell shape (s=0, p=1, d=2, f=3) | 亚层形状
Magnetic | 磁量子数	mₗ	–ℓ … 0 … +ℓ	Orbital orientation | 轨道取向
Spin | 自旋量子数	mₛ	+½ or –½	Spin direction (↑ or ↓) | 自旋方向

No two electrons in the same atom can have an identical set of all four quantum numbers – this is the basis of the Pauli Exclusion Principle. In IB and CCEA exams, you are not required to assign all quantum numbers to each electron in a complex atom, but you must understand their meaning and how they relate to orbital capacities (e.g. a d-subshell has ℓ = 2 and five possible mₗ values, so it can hold 10 electrons).

同一原子中不能有两个电子拥有完全相同的一组四个量子数——这正是泡利不相容原理的基础。在 IB 和 CCEA 考试中，你不需要为复杂原子中的每一个电子分配所有量子数，但你必须理解它们的含义以及它们与轨道容量的关系（例如 d 亚层的 ℓ = 2，有五个可能的 mₗ 值，因此最多可容纳 10 个电子）。

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3. Energy Levels and Sublevels | 能级与亚层

The principal quantum number n divides the electron cloud into main energy levels (shells). Each shell contains n subshells. For n = 1, only an s-subshell exists; for n = 2, s and p subshells; for n = 3, s, p and d; and for n = 4, s, p, d and f. The energy ordering of subshells, however, does not simply follow the value of n alone.

主量子数 n 将电子云划分为主能级（电子层）。每个主层包含 n 个亚层。当 n = 1 时，只存在 s 亚层；n = 2 时有 s 和 p 亚层；n = 3 时有 s、p、d 亚层；n = 4 时有 s、p、d、f 亚层。但亚层的能量顺序并非仅由 n 值决定。

The s sublevel holds a maximum of 2 electrons, p holds 6, d holds 10, and f holds 14. Orbitals within the same sublevel (e.g. the three p-orbitals) are degenerate – they have identical energy in an isolated atom. In multi-electron atoms, sublevel energies overlap; for instance, the 4s sublevel is lower in energy than 3d, which leads to the 4s filling before 3d in potassium and calcium.

s 亚层最多容纳 2 个电子，p 容纳 6 个，d 容纳 10 个，f 容纳 14 个。同一亚层内的轨道（例如三个 p 轨道）是简并的，即它们在孤立原子中能量相同。在多电子原子中，亚层的能量出现交错；例如 4s 亚层的能量低于 3d，这就导致钾和钙中 4s 先于 3d 被填充。

Energy order: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s …

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4. The Aufbau Principle | 构造原理

The Aufbau principle states that electrons occupy the lowest energy orbitals available first. An atom is ‘built up’ by placing electrons into orbitals in order of increasing energy, starting from 1s. This principle, together with the (n + ℓ) rule, gives the filling sequence you need to memorise for the first 36 elements.

构造原理指出，电子会优先占据能量最低的可用轨道。原子通过按能量递增的顺序将电子填入轨道而“构建”起来，从 1s 开始。这一原理结合 (n + ℓ) 规则，给出了你需要记住的前 36 号元素的填充顺序。

The (n + ℓ) rule is a useful guide: the energy of a subshell increases with increasing n + ℓ; and for two subshells with the same n + ℓ, the one with lower n has lower energy. For example, 3d (n + ℓ = 3 + 2 = 5) is higher in energy than 4s (n + ℓ = 4 + 0 = 4), so 4s fills first. For exams, you can use a simple diagonal diagram or follow the order given above.

(n + ℓ) 规则是一个有用的指导：亚层能量随 n + ℓ 值增大而升高；当两个亚层 n + ℓ 值相同，则 n 较小的亚层能量更低。例如，3d (n + ℓ = 3 + 2 = 5) 的能量高于 4s (n + ℓ = 4 + 0 = 4)，因此 4s 先填。考试中你可以借助简单的斜向填充图或遵循上述顺序。

The Aufbau principle works perfectly for the vast majority of neutral atoms. However, it is the starting point; deviations will be discussed later in the context of chromium and copper, where the stability of half-filled and fully filled d-subshells becomes relevant.

构造原理对绝大多数中性原子完全适用。但它只是一个起点；后续在讨论铬和铜时我们会讲到偏离现象，其中半满和全满 d 亚层的特殊稳定性起关键作用。

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5. Hund’s Rule | 洪特规则

Hund’s rule of maximum multiplicity states that when electrons are added to degenerate orbitals (orbitals of the same energy), they first occupy separate orbitals singly, with parallel spins, before any orbital receives a second electron. This arrangement minimises electron–electron repulsion and gives the lowest energy configuration.

洪特规则（最大多重度规则）指出，当电子填入简并轨道（能量相同的轨道）时，电子会首先以平行自旋的方式单独占据不同轨道，在每一个轨道都已有一个电子之后，才会在某个轨道中填入第二个电子。这种排布方式使电子间排斥力最小，能量最低。

For example, the nitrogen atom (Z = 7) has the configuration 1s² 2s² 2p³. The three 2p electrons occupy all three p-orbitals (2pₓ, 2pᵧ, 2p₂) singly, all with spin up (↑). In an orbital box diagram you would see three half-filled p-boxes, never a pair in one box and one electron elsewhere. This rule is frequently tested in both multiple-choice and structured questions.

例如，氮原子 (Z = 7) 的排布为 1s² 2s² 2p³。三个 2p 电子分别单独占据三个 p 轨道 (2pₓ, 2pᵧ, 2p₂)，且自旋方向相同（↑）。在轨道框图中你会看到三个半满的 p 框，绝不会出现一个框内配对、另一个框只有单个电子的情形。这一规则在选择题和结构化问题中经常考察。

The parallel spin requirement arises from the spin quantum number, mₛ. Electrons with parallel spins have the same mₛ value and experience less coulombic repulsion because their spatial distributions keep them apart more effectively. This is a quantum mechanical consequence of the exchange interaction.

平行自旋的要求源自自旋量子数 mₛ。具有平行自旋的电子因空间分布能更有效地相互远离，从而减小库仑排斥。这是交换相互作用在量子力学中的表现。

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6. Pauli Exclusion Principle | 泡利不相容原理

The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of all four quantum numbers. In practical terms, this means an atomic orbital can hold a maximum of two electrons, and those two electrons must have opposite spins (mₛ = +½ and –½).

泡利不相容原理指出，同一原子中不能有两个电子拥有完全相同的一组四个量子数。在实际中，这意味着一个原子轨道最多只能容纳两个电子，且这两个电子的自旋必须相反（mₛ = +½ 和 –½）。

An orbital box diagram illustrates this clearly: an empty box represents an orbital; an arrow pointing upwards (↑) represents one electron with spin +½; an arrow pointing downwards (↓) represents the second electron with spin –½. You will never see two arrows pointing the same direction in a single orbital box.

轨道框图可以清晰地说明这一点：一个空框代表一个轨道；向上箭头 (↑) 表示一个自旋为 +½ 的电子；向下箭头 (↓) 表示第二个自旋为 –½ 的电子。你绝不会在一个轨道框中看到两个方向相同的箭头。

When writing electron configurations, the exclusion principle determines the maximum occupancy of each subshell. For example, a full 2p subshell is written as 2p⁶, not 2p⁷ or 2p⁸. In marking schemes, violating this principle – such as placing three electrons in a single p-orbital box – leads to an automatic deduction.

在书写电子排布时，不相容原理决定了每个亚层的最大电子数。例如，填满的 2p 亚层写作 2p⁶，而不是 2p⁷ 或 2p⁸。在评分方案中，违反这一原理——例如在单个 p 轨道框中放进三个电子——会被直接扣分。

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7. Writing spdf Notation | 书写 spdf 排布式

The spdf notation is the standard way to represent electron configurations. It lists the occupied subshells in order of increasing energy (or by principal quantum number, depending on the examination board), with the number of electrons in each subshell shown as a superscript. For IB and CCEA, you are usually expected to write configurations in order of increasing n, for example, titanium (Z = 22) as 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d².

spdf 记法是表示电子排布的标准方式。它按能量递增顺序（或按主量子数顺序，视考试局要求而定）列出已占据的亚层，并以右上标数字表示每个亚层的电子数。对于 IB 和 CCEA，通常要求按 n 值递增的顺序书写，例如钛 (Z = 22) 写作 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d²。

Some specifications prefer the subshells to be written in order of increasing principal quantum number rather than the filling order. This means the 3d is placed before 4s in elements beyond scandium. Check your syllabus: many IB questions accept either ordering as long as the total number of electrons is correct, but CCEA often favours the ‘n’ order. Always show 3d before 4s when writing the full electronic configuration of a transition metal after filling.

有些考试大纲要求按主量子数递增的顺序书写亚层，而不是按填充顺序。这意味着在钪之后的元素中，3d 要写在 4s 之前。请查阅你的教学大纲：许多 IB 题目只要电子总数正确即可接受两种顺序，但 CCEA 通常倾向于按 n 的顺序。在书写过渡金属填满后的完整电子排布时，一般将 3d 放在 4s 前面。

Examples:
Neon (Ne, Z=10): 1s² 2s² 2p⁶
Chlorine (Cl, Z=17): 1s² 2s² 2p⁶ 3s² 3p⁵
Vanadium (V, Z=23): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s²
When you are confident with neutral atoms, move on to ions, which require careful handling of electron removal sequence.

例如：
氖 (Ne, Z=10): 1s² 2s² 2p⁶
氯 (Cl, Z=17): 1s² 2s² 2p⁶ 3s² 3p⁵
钒 (V, Z=23): 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s²
当你对中性原子熟练后，就可以学习离子的电子排布，这需要小心处理电子失去的顺序。

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8. Orbital Box Diagrams | 轨道框图

Orbital box diagrams (also called orbital filling diagrams) represent each orbital as a box and each electron as an arrow. They show the application of Hund’s rule and the Pauli principle visually and are frequently required in exam questions to explain magnetic behaviour or to identify incorrect configurations.

轨道框图（也称轨道填充图）将每个轨道表示成一个方框，每个电子表示成一个箭头。它们直观地展示了洪特规则和泡利原理的应用，考试中经常要求用框图来解释磁性行为或识别错误排布。

When drawing box diagrams, the key conventions are: label each set of boxes with the subshell name (1s, 2s, 2p, etc.); draw the required number of boxes (1 for s, 3 for p, 5 for d); fill electrons singly with parallel spins before pairing; and never place two arrows of the same spin direction in the same box.

在绘制框图时，关键约定是：给每组方框标上亚层名称（1s、2s、2p 等）；画出所需数量的方框（s 有 1 个框，p 有 3 个框，d 有 5 个框）；填充电子时先以平行自旋单独填满所有框，然后再配对；绝不在同一个框中放入两个自旋方向相同的箭头。

For oxygen (Z=8), the configuration is 1s² 2s² 2p⁴. The p-orbitals will show two of the three boxes containing a pair, and one box containing a single electron with two opposite spins in the paired boxes and one unpaired electron. This reveals that oxygen is paramagnetic due to two unpaired electrons. Box diagrams are excellent for identifying paramagnetism (unpaired electrons) versus diamagnetism (all electrons paired).

对于氧 (Z=8)，排布为 1s² 2s² 2p⁴。p 轨道会显示三个框中有两个框含有一对电子（两个箭头方向相反），一个框含有一个单电子。这揭示了氧因有两个未成对电子而具有顺磁性。框图是识别顺磁性（有未成对电子）和抗磁性（所有电子配对）的极好工具。

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9. Noble Gas Shorthand | 惰性气体简写式

Writing out full configurations for heavy elements can be tedious. The noble gas core notation allows you to abbreviate the inner filled shells by using the symbol of the preceding noble gas in square brackets, followed by the valence and outer subshells. For example, iron (Fe, Z=26) can be written as [Ar] 4s² 3d⁶.

对于较重元素，写出完整的电子排布可能很繁琐。惰性气体简写法允许你使用前一个惰性气体的符号加方括号来表示内部已填满的电子层，然后写上价层和外部的亚层。例如，铁 (Fe, Z=26) 可表示为 [Ar] 4s² 3d⁶。

The noble gas to use is the one with the atomic number closest to but less than that of the target element. For all elements in period 4, the core is [Ar] (Z=18). For period 5, it is [Kr] (Z=36). For exam success, you must be able to write both the full configuration and the shorthand version correctly; failing to use the correct noble gas is a common mistake.

选择的惰性气体应该是原子序数最接近目标元素但又小于它的那一个。对于第四周期的所有元素，内核是 [Ar] (Z=18)；第五周期是 [Kr] (Z=36)。考试中你需要能正确写出完整排布式和简写式；使用错误的惰性气体是一个常见错误。

In shorthand notation, the outer electrons are written in the order of the remaining configuration. For transition metals, if the exam board prefers n order, then Fe becomes [Ar] 3d⁶ 4s². Always consult past papers to determine the expected format, but both orders often gain credit in IB; CCEA mark schemes usually adopt the 3d before 4s convention for shorthand.

在简写式中，外层电子按剩余排布的顺序书写。对于过渡金属，如果考试局倾向于按 n 的顺序，那么 Fe 应写作 [Ar] 3d⁶ 4s²。请务必查阅历年试题以确定要求的格式，不过 IB 中两种顺序通常都得分；CCEA 的评分方案通常采用简写式中 3d 先于 4s 的写法。

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10. Ions: Cations and Anions | 离子的电子排布

When forming ions, electrons are removed from (or added to) the highest-energy orbitals first. For cations of main-group elements, electrons are lost from the outermost shell, i.e., the subshell with the highest n value. For example, sodium (Na) forms Na⁺ by losing the single 3s electron: Na [Ne] 3s¹ → Na⁺ [Ne] or 1s² 2s² 2p⁶.

当形成离子时，电子首先从能量最高的轨道中失去（或添加到其中）。对于主族元素的阳离子，电子从最外层，即 n 值最大的亚层中失去。例如，钠 (Na) 失去一个 3s 电子形成 Na⁺：Na [Ne] 3s¹ → Na⁺ [Ne] 或 1s² 2s² 2p⁶。

For transition metal cations, electrons are always removed from the 4s subshell before the 3d, even though 4s fills first. This is because once the 3d begins to fill, the 4s subshell becomes higher in energy. The correct order for Fe²⁺ (Z=26) is: Fe [Ar] 4s² 3d⁶ → Fe²⁺ [Ar] 3d⁶, removing the two 4s electrons. Memorise this rule; it is one of the most tested concepts in redox and transition metal chemistry.

对于过渡金属阳离子，电子总是先从 4s 亚层失去，然后才从 3d 失去，尽管 4s 填充电子的顺序在先。这是因为一旦 3d 开始填充，4s 亚层的能量会变得高于 3d。正确的 Fe²⁺ (Z=26) 排布为：Fe [Ar] 4s² 3d⁶ → Fe²⁺ [Ar] 3d⁶，即失去两个 4s 电子。请牢记这一规则，它是在氧化还原和过渡金属化学中考查最多的知识点之一。

Anions are formed by adding electrons to the lowest-energy empty or partially filled orbitals. For example, oxygen (O, 1s² 2s² 2p⁴) gains two electrons to form O²⁻ [He] 2s² 2p⁶, achieving the neon configuration. Always draw or write the parent atom’s configuration first, then add or remove electrons according to the charge, while respecting the rules of removal sequence for transition metals.

阴离子的形成则是将电子添加到能量最低的空轨道或半满轨道中。例如，氧 (O, 1s² 2s² 2p⁴) 获得两个电子形成 O²⁻ [He] 2s² 2p⁶，达到氖的构型。在作答时，先写出母原子的排布，然后根据电荷添加或移除电子，同时遵守过渡金属的失去电子顺序规则。

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11. Anomalous Configurations: Chromium and Copper | 异常排布：铬和铜

Chromium (Cr, Z=24) and copper (Cu, Z=29) exhibit exceptional electron configurations because of the extra stability associated with half-filled (d⁵) and fully filled (d¹⁰) d-subshells. The Aufbau prediction for Cr would be [Ar] 4s² 3d⁴, but the actual configuration is [Ar] 4s¹ 3d⁵.

铬 (Cr, Z=24) 和铜 (Cu, Z=29) 表现出异常的电子排布，原因在于半满 (d⁵) 和全满 (d¹⁰) d 亚层具有额外的稳定性。若按构造原理预测，Cr 应为 [Ar] 4s² 3d⁴，但实际的排布是 [Ar] 4s¹ 3d⁵。

The energy gained by promoting one 4s electron into the 3d set to achieve a half-filled 3d subshell outweighs the cost of moving the electron to a slightly higher energy orbital. The symmetrical distribution of electrons and the exchange energy stabilisation drive this behaviour. Similarly, copper adopts [Ar] 4s¹ 3d¹⁰ instead of the expected [Ar] 4s² 3d⁹ in order to achieve a completely filled d-subshell.

将一个 4s 电子激发到 3d 轨道中以实现半满 3d 亚层所获得的能量，超过了将该电子移动到稍高能量轨道所付出的代价。电子的对称分布和交换能的稳定作用驱动了这一行为。类似地，铜采用 [Ar] 4s¹ 3d¹⁰ 而非预期的 [Ar] 4s² 3d⁹，以达到全满的 d 亚层。

Exam questions will often ask you to write the configuration of Cr and Cu from first principles and to explain the anomaly. Other elements such as molybdenum (Mo) and silver (Ag) in the same groups show similar patterns, but for IB and CCEA, Cr and Cu are the most common. When writing the ions of these anomalous atoms, apply the same cation removal rule: Cu⁺ is [Ar] 3d¹⁰, Cu²⁺ is [Ar] 3d⁹.Published by TutorHao | IB Chemistry Revision Series | aleveler.com

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