Electron Configuration in A-Level Chemistry | A-Level 化学：电子排布考点精讲

📚 Electron Configuration in A-Level Chemistry | A-Level 化学：电子排布考点精讲

Electron configuration is the arrangement of electrons in an atom’s shells and subshells, and it underpins almost every aspect of chemical behaviour — from an element’s reactivity to its bonding patterns and magnetic properties. In A-Level Chemistry, you are expected not only to write out configurations for atoms and ions up to krypton (and beyond, for selected transition metals) but also to justify them using the Aufbau principle, Hund’s rule and the Pauli exclusion principle. This article provides a structured revision guide covering all the key points, common pitfalls and examination tips.

电子排布描述了原子中电子在壳层和亚层中的分布方式，它几乎决定了元素的所有化学行为——从反应活性到成键方式乃至磁性。在A-Level化学中，你需要能够书写从氢到氪（以及部分过渡金属）的原子和离子的电子排布式，并且会用构造原理、洪特规则和泡利不相容原理进行解释。本文提供了一套结构化的复习指南，涵盖所有关键考点、常见错误和考试技巧。

1. Energy Levels and Sub-shells | 能级与亚层

Electrons occupy principal energy levels (shells) labelled n = 1, 2, 3, 4 … Within each shell, there are sub-shells designated as s, p, d and f. The first shell (n=1) contains only an s sub-shell; the second (n=2) contains s and p sub-shells; the third (n=3) contains s, p and d sub-shells; and the fourth (n=4) contains s, p, d and f sub-shells.

电子占据用主量子数 n = 1, 2, 3, 4 … 标记的能级（壳层）。每个壳层内又分为亚层，记为 s, p, d, f。第一壳层 (n=1) 只有一个 s 亚层；第二壳层 (n=2) 有 s 和 p 亚层；第三壳层 (n=3) 有 s, p, d 亚层；第四壳层 (n=4) 有 s, p, d, f 亚层。

Each type of sub-shell can hold a maximum number of electrons: s holds 2, p holds 6, d holds 10 and f holds 14. This arises from the number of orbitals in each sub-shell: s has 1 orbital, p has 3, d has 5 and f has 7, with each orbital accommodating a maximum of two electrons.

每种亚层能够容纳的电子数目不同：s 容纳 2 个，p 容纳 6 个，d 容纳 10 个，f 容纳 14 个。其原因在于各亚层包含的轨道数：s 有 1 个轨道，p 有 3 个，d 有 5 个，f 有 7 个，而每个轨道最多容纳两个电子。

The energy of sub-shells within a given shell increases in the order s < p < d < f. However, when we consider different shells, the energetic order can overlap — for example, the 4s sub-shell is lower in energy than the 3d sub-shell, which is why the 4s orbital fills before 3d.

在同一壳层内，亚层的能量大小顺序为 s < p < d < f。但当涉及不同壳层时，能量顺序会发生重叠——例如 4s 亚层的能量低于 3d 亚层，因此 4s 轨道先于 3d 被填充。

2. Atomic Orbitals: s, p, d and f | 原子轨道：s, p, d 和 f

An atomic orbital is a region around the nucleus where there is a high probability of finding an electron. Each orbital can hold up to two electrons. An s orbital is spherical in shape. Every shell has one s orbital, starting from n=1.

原子轨道是原子核外电子出现概率较高的空间区域。每个轨道最多可容纳两个电子。s 轨道呈球形。每个壳层都有一个 s 轨道，从 n=1 开始。

There are three p orbitals: p_x, p_y and p_z, each with a dumbbell shape and aligned along the x, y and z axes, respectively. They are all degenerate (equal in energy).

p 轨道有三个：p_x、p_y 和 p_z，每个呈哑铃形，分别沿 x、y、z 轴方向伸展。它们是简并的（能量相等）。

d orbitals begin at n=3. There are five d orbitals, with more complex shapes. In an isolated atom, all five are degenerate; in a chemical environment they can be split into different energy groups. The f orbitals, encountered at n=4 and above, consist of seven degenerate orbitals with even more intricate shapes.

d 轨道从 n=3 开始出现。共有五个 d 轨道，形状较为复杂。在孤立的原子中，这五个轨道是简并的；在化学环境中它们可能分裂成不同的能级组。f 轨道在 n=4 及以上出现，包含七个简并轨道，形状更加复杂。

3. The Aufbau Principle | 构造原理

The Aufbau principle states that electrons fill atomic orbitals of the lowest available energy before occupying higher-energy ones. The order of filling can be determined from the (n + l) rule or the diagonal rule diagram. The sequence runs: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p …

构造原理指出，电子在占据较高能量轨道之前，会先填充能量最低的可用轨道。填充顺序可以通过 (n + l) 规则或斜线图来确定。顺序为：1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p …

You should memorise that 4s fills before 3d. This is crucial for the first transition series. When writing configurations for atoms like potassium and calcium, the 4s orbital fills first: K [Ar] 4s¹, Ca [Ar] 4s². For scandium onwards, the 3d orbitals are populated.

你必须牢记 4s 先于 3d 填充。这对第一过渡系至关重要。书写钾、钙等原子的排布式时，4s 轨道先填：K [Ar] 4s¹, Ca [Ar] 4s²。从钪开始，3d 轨道才开始填入电子。

4. Hund’s Rule of Maximum Multiplicity | 洪特规则（最大多重度）

Hund’s rule states that when filling degenerate orbitals (orbitals of the same energy, such as the three p orbitals or the five d orbitals), electrons will first occupy separate orbitals with parallel spins before any pairing occurs. This minimises electron-electron repulsion and yields the lowest energy arrangement.

洪特规则指出，对于简并轨道（能量相等的轨道，如三个 p 轨道或五个 d 轨道），电子会优先以自旋平行的方式单独占据各个轨道，然后才进行配对。这样可以最大程度地减小电子间排斥力，得到能量最低的排布。

For nitrogen (Z=7), the configuration is 1s² 2s² 2p³. The three 2p electrons occupy the three p orbitals singly, all with the same spin direction, giving three unpaired electrons. This can be shown in an orbital box diagram with arrows.

以氮 (Z=7) 为例，其电子排布为 1s² 2s² 2p³。三个 2p 电子各自单独占据一个 p 轨道，且自旋方向相同，因此氮原子有三个未成对电子。这可以在轨道方框图中用箭头表示。

5. The Pauli Exclusion Principle | 泡利不相容原理

The Pauli exclusion principle states that no two electrons in the same atom can have the same set of four quantum numbers. In practical terms, this means an orbital can hold a maximum of two electrons, and they must have opposite spins (one spin-up, one spin-down).

泡利不相容原理指出，同一个原子中不可能有两个电子具有完全相同的四个量子数。实际应用中，这意味着一个轨道最多能容纳两个电子，且这两个电子必须自旋相反（一个向上，一个向下）。

Thus, within one orbital, two electrons will be represented as a pair of opposed arrows ( ) in an orbital diagram. This principle is essential for understanding the build-up of the periodic table and for writing correct configurations.

因此，在轨道图中，一个轨道内的两个电子用一对反向箭头表示。这个原理对于理解周期表的构建和书写正确的电子排布式至关重要。

6. Writing Electron Configurations | 书写电子排布式

Electron configurations can be written in full notation, e.g. sodium (Z=11): 1s² 2s² 2p⁶ 3s¹. Sub-shell energy order is followed, and superscripts indicate the number of electrons in each sub-shell. The total of superscripts must equal the atomic number for a neutral atom.

电子排布可以用完整形式书写，例如钠 (Z=11): 1s² 2s² 2p⁶ 3s¹。遵循亚层能量顺序，上标数字表示该亚层的电子数。对中性原子，上标数字之和必须等于原子序数。

For elements beyond argon, a noble-gas core notation (shorthand) is often used. For example, iron (Z=26) can be written as [Ar] 4s² 3d⁶. The symbol [Ar] represents the configuration of argon: 1s² 2s² 2p⁶ 3s² 3p⁶.

对于氩以后的元素，常使用稀有气体短写法（核式）。例如铁 (Z=26) 可写作 [Ar] 4s² 3d⁶。符号 [Ar] 代表氩的电子构型：1s² 2s² 2p⁶ 3s² 3p⁶。

When writing configurations for transition metal atoms, always write the 4s sub-shell before the 3d sub-shell according to the filling order, but be aware that for ions the 4s electrons may be lost first. A common examination requirement is to give both the full and abbreviated configurations for elements up to krypton.

书写过渡金属原子的排布时，按照填充顺序，总是先写 4s 亚层再写 3d 亚层。但要注意，形成离子时 4s 电子通常先失去。考试中常见的考查方式包括要求写出直到氪的元素的全排布和简写排布。

7. Orbital Box Diagrams | 轨道方框图

In orbital box (or arrow-in-box) diagrams, each orbital is represented by a box, and electrons are shown as arrows: spin-up ( ) and spin-down ( ). The boxes for degenerate orbitals are drawn side by side. These diagrams make it easy to apply Hund’s rule and the Pauli principle visually.

在轨道方框图（箭头箱图）中，每个轨道用一个方框表示，电子用箭头表示：自旋向上和自旋向下。简并轨道的方框并排画出。这种图可直观地体现洪特规则和泡利原理。

For oxygen (1s² 2s² 2p⁴), the 2p sub-shell diagram shows: three boxes for 2p_x, 2p_y and 2p_z. According to Hund’s rule, you place the first three electrons singly with parallel spins, then the fourth pairs up in one box with opposite spin. This gives two unpaired electrons, explaining oxygen’s paramagnetism.

以氧（1s² 2s² 2p⁴）为例，其 2p 亚层方框图显示：三个方框分别代表 2p_x, 2p_y, 2p_z。根据洪特规则，前三个电子以平行自旋单独填入，第四个电子以反向自旋与其中一个配对。这样氧原子有两个未成对电子，解释了氧的顺磁性。

8. Electronic Configurations of Ions | 离子的电子排布

When forming positive ions (cations), electrons are removed from the highest energy occupied orbital. For transition metals, this means 4s electrons are removed before 3d electrons. For example, Fe: [Ar] 4s² 3d⁶; Fe²⁺: [Ar] 3d⁶; Fe³⁺: [Ar] 3d⁵.

形成正离子时，电子从能量最高的已占轨道中移除。对于过渡金属，这意味着 4s 电子先于 3d 电子失去。例如 Fe 原子：[Ar] 4s² 3d⁶；Fe²⁺：[Ar] 3d⁶；Fe³⁺：[Ar] 3d⁵。

Negative ions (anions) are formed by adding electrons to the neutral atom’s configuration. Added electrons occupy the next available vacant orbital according to the Aufbau order. For instance, O: 1s² 2s² 2p⁴; O²⁻: 1s² 2s² 2p⁶ (same as neon).

负离子（阴离子）是通过向中性原子添加电子形成的。添加的电子按照构造原理填充到下一个可用空轨道。例如 O：1s² 2s² 2p⁴；O²⁻：1s² 2s² 2p⁶（与氖相同）。

Isoelectronic species possess the same number of electrons and therefore often share the same electronic configuration. For example, F⁻, Ne, and Na⁺ all have the configuration 1s² 2s² 2p⁶.

等电子体具有相同的电子数，因而往往具有相同的电子排布式。例如 F⁻、Ne 和 Na⁺ 的排布都是 1s² 2s² 2p⁶。

9. The Periodic Table and Electron Configuration | 周期表与电子排布

The periodic table is divided into blocks that directly correspond to the type of sub-shell being filled. The s-block contains Groups 1 and 2 (outer s sub-shell being filled); the p-block contains Groups 13 to 18 (outer p sub-shell being filled); the d-block comprises transition metals (inner d sub-shell being filled); and the f-block consists of lanthanides and actinides (inner f sub-shell).

周期表按填充的亚层类型划分为不同的区。s 区包括第 1、2 族（最外层 s 亚层被填充）；p 区包括第 13 至 18 族（最外层 p 亚层被填充）；d 区为过渡金属（内层 d 亚层被填充）；f 区为镧系和锕系元素（内层 f 亚层被填充）。

The period number corresponds to the highest principal quantum number n being occupied. An element’s group number (for s-block and p-block) often indicates the number of electrons in the outermost shell: Group 1 has ns¹, Group 2 has ns², Group 13 has ns² np¹, and so on.

周期数对应于电子所占据的最高主量子数 n。对于 s 区和 p 区元素，族数通常表示最外层电子数：第 1 族为 ns¹，第 2 族为 ns²，第 13 族为 ns² np¹，以此类推。

This relationship allows you to deduce an element’s electronic configuration from its position in the periodic table, and vice versa — a key skill tested in A-Level exams.

这种对应关系使得你可以根据元素在周期表中的位置推断其电子排布，反之亦然——这是A-Level考试中经常考查的关键技能。

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

Chromium (Z=24) and copper (Z=29) are the two standard examples of anomalous electron configurations in the first transition series. Instead of the expected [Ar] 4s² 3d⁴, chromium adopts [Ar] 4s¹ 3d⁵. Copper, instead of [Ar] 4s² 3d⁹, is [Ar] 4s¹ 3d¹⁰.

铬 (Z=24) 和铜 (Z=29) 是第一过渡系中两个经典的电子排布异常例子。铬的实际排布是 [Ar] 4s¹ 3d⁵，而非预期的 [Ar] 4s² 3d⁴。铜的实际排布是 [Ar] 4s¹ 3d¹⁰，而非 [Ar] 4s² 3d⁹。

The extra stability is attributed to the half-filled (3d⁵) or fully filled (3d¹⁰) d sub-shell, which provides a symmetrical electron distribution and a lower-energy state. This is often explained in terms of exchange energy and reduced repulsion.

这种额外的稳定性归因于半充满 (3d⁵) 或全充满 (3d¹⁰) 的 d 亚层，它们具有对称的电子分布和较低的能量。这通常用交换能和更小的排斥作用来解释。

In examinations, you may be asked to write the configurations for Cr and Cu atoms, and for their ions. For Cr²⁺, remove the 4s electron plus one d electron: [Ar] 3d⁴. For Cu⁺, the ion is [Ar] 3d¹⁰.

考试中可能会要求写出 Cr 和 Cu 原子及其离子的电子排布。对于 Cr²⁺，先失去 4s 电子再失去一个 d 电子，排布为 [Ar] 3d⁴。Cu⁺ 则为 [Ar] 3d¹⁰。

11. Ionisation Energies as Evidence | 电离能作为证据

Successive ionisation energy data provide strong experimental evidence for the shell and sub-shell model of electron configuration. A large jump in ionisation energy indicates the removal of an electron from a new, lower energy shell or a more stable configuration.

逐级电离能数据为电子排布的壳层和亚层模型提供了有力的实验证据。电离能的突增表示电子从一个新的、更稳定的低能量壳层或构型中移出。

For example, the huge increase between the fourth and fifth ionisation energies of silicon (1s² 2s² 2p⁶ 3s² 3p²) shows that the fifth electron is being removed from the 2p sub-shell, which is closer to the nucleus and much more strongly held than the outer 3p and 3s electrons.

例如，硅的第四和第五电离能之间存在巨大的跃升（硅的电子排布为 1s² 2s² 2p⁶ 3s² 3p²），这表明第五个电子是从 2p 亚层中被移除的，该亚层更靠近原子核，受到的束缚远大于外层的 3p 和 3s 电子。

Similarly, the drop in first ionisation energy from beryllium to boron and from nitrogen to oxygen can be explained by the relative energies of s and p orbitals, and the effect of electron pairing in a p orbital.

与此类似，第一电离能从铍到硼以及从氮到氧的下降，可以用 s 和 p 轨道的相对能量以及 p 轨道中电子配对效应来解释。

Plotting log ionisation energy against the number of the electron removed yields clear steps that match the predicted electron configuration for any given element.

以电离能的对数对移去的电子数作图，会显示出清晰的分层，这些分层与元素所预测的电子排布完全吻合。

12. Summary and Key Points | 总结与要点

To master electron configuration at A-Level, remember the Aufbau filling order, Hund’s rule and the Pauli principle. Practise writing full, noble-gas-shorthand and orbital box diagrams for atoms and ions. Pay particular attention to the 4s/3d interplay and the exceptions Cr and Cu. Use ionisation energy trends to rationalise configurations and reinforce your understanding.

要在A-Level中掌握电子排布，须牢记构造原理填充顺序、洪特规则和泡利原理。多练习书写原子和离子的完整排布式、稀有气体简写式和轨道方框图。特别注意 4s/3d 的能量交错以及 Cr 和 Cu 的异常情况。运用电离能的变化趋势来解释电子排布，巩固你的理解。

Key points checklist:

要点清单：

s, p, d, f sub-shell capacities: 2, 6, 10, 14

s, p, d, f 亚层最多容纳电子数：2, 6, 10, 14
Filling order: 1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p …

填充顺序：1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p …
Hund’s rule: single occupancy of degenerate orbitals before pairing

洪特规则：电子在简并轨道中先单独占据再配对
Cr: [Ar] 4s¹ 3d⁵; Cu: [Ar] 4s¹ 3d¹⁰

Cr 的排布：[Ar] 4s¹ 3d⁵；Cu 的排布：[Ar] 4s¹ 3d¹⁰
For cations, lose 4s electrons before 3d

对于阳离子，先失去 4s 电子再失去 3d 电子
Ionisation energy jumps confirm electronic structure

电离能跃升验证电子层结构

Published by TutorHao | Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Electron Configuration in A-Level Chemistry | A-Level 化学：电子排布 考点精讲