📚 A-Level WJEC Chemistry: Electron Configuration Exam Essentials | A-Level WJEC 化学：电子排布 考点精讲
Electron configuration is the arrangement of electrons in the shells and subshells of an atom. It determines chemical properties, bonding and reactivity, making it a foundational topic for A-Level WJEC Chemistry. Understanding electron configuration enables you to predict trends across the periodic table and to explain experimental evidence such as ionisation energies.
电子排布是指电子在原子壳层和亚层中的排列方式。它决定了化学性质、键合和反应活性，是 A-Level WJEC 化学的基础主题。理解电子排布可以让你预测周期表中的变化趋势，并解释电离能等实验证据。
1. Introduction to Electron Configuration | 电子排布简介
Every electron in an atom occupies a region of space called an orbital, defined by a unique set of quantum numbers. The way electrons are distributed among orbitals is known as the electron configuration. For WJEC, you need to write configurations for atoms and ions up to krypton (Z=36), understand orbital diagrams and apply principles that govern electron filling.
原子中的每一个电子都占据着一个称为轨道的空间区域，由一组独特的量子数定义。电子在轨道中的分布方式称为电子排布。在 WJEC 考试中，你需要写出直到氪（Z=36）的原子和离子的排布，理解轨道图，并应用决定电子填充的原理。
You will be expected to link electron configuration to the periodic table, explain anomalies like chromium and copper, and interpret data from successive ionisation energies. This topic forms the bridge between atomic structure and bonding.
你将要能够把电子排布与周期表联系起来，解释铬和铜等异常现象，并能解读逐级电离能的数据。这个主题是原子结构和化学键之间的桥梁。
2. Energy Levels and Orbitals | 能级与轨道
Electrons are arranged in principal energy levels (shells) numbered n=1, 2, 3, 4… Each shell contains subshells labelled s, p, d and f. The number of subshells in a shell equals n: shell 1 has only 1s; shell 2 has 2s and 2p; shell 3 has 3s, 3p and 3d; shell 4 has 4s, 4p, 4d and 4f.
电子按主能级（壳层）排列，主量子数 n=1, 2, 3, 4… 每个壳层包含标记为 s、p、d 和 f 的亚层。一个壳层中亚层的数量等于 n：壳层 1 只有 1s；壳层 2 有 2s 和 2p；壳层 3 有 3s、3p 和 3d；壳层 4 有 4s、4p、4d 和 4f。
Within a shell, the subshell energy order is s < p < d < f. However, the energy of a 4s orbital is slightly lower than that of 3d, which leads to the 4s filling before 3d. This is crucial for transition metals. The relative energies can be remembered by the (n+l) rule or by using the diagonal rule diagram.
在同一壳层内，亚层能量顺序为 s < p < d < f。但是，4s 轨道的能量略低于 3d，因此 4s 比 3d 先被填充。这对过渡金属至关重要。相对能量可以通过 (n+l) 规则或对角线规则图来记忆。
Energy order: 1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s ...
能量顺序：1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s ...
3. s, p, d Orbitals: Shapes and Capacity | s, p, d 轨道：形状与容量
An s orbital is spherical. Each s subshell contains one orbital, which can hold a maximum of two electrons. A p subshell has three dumbbell-shaped orbitals (pₓ, pᵧ, p₂), each at right angles, holding up to six electrons in total. A d subshell has five orbitals, holding up to ten electrons.
s 轨道是球形的。每个 s 亚层包含一个轨道，最多容纳两个电子。p 亚层有三个哑铃形轨道（pₓ、pᵧ、p₂），彼此成直角，总共最多容纳六个电子。d 亚层有五个轨道，最多容纳十个电子。
The WJEC specification expects you to know the shapes of s and p orbitals and to draw simple boundary surface diagrams. You must also recall the electron capacities: s: 2, p: 6, d: 10, f: 14. This links directly to the number of elements in each block of the periodic table.
WJEC 考试大纲要求你了解 s 和 p 轨道的形状，并能画出简单的边界表面图。你还必须记住电子容量：s: 2, p: 6, d: 10, f: 14。这与周期表中每个区元素的数量直接相关。
4. Aufbau Principle and Orbital Filling | 构造原理与轨道填充
The Aufbau principle states that electrons fill orbitals of the lowest available energy first. For an atom, this means 1s fills before 2s, 2p before 3s, and critically 4s before 3d. It provides a systematic way to build up the electron configuration from hydrogen onwards.
构造原理指出，电子首先填充可用的最低能量轨道。对于原子，这意味着 1s 在 2s 之前填充，2p 在 3s 之前填充，并且关键的是 4s 在 3d 之前填充。它为从氢开始逐步构建电子排布提供了一种系统的方法。
When writing configurations, you must follow the energy sequence. For example, potassium (Z=19) is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹, not 3d¹. The 4s subshell fills before 3d because it has slightly lower energy. This pattern holds for the first row of the d-block despite common misconceptions.
在书写排布时，你必须遵循能量序列。例如，钾（Z=19）的排布是 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹，而不是 3d¹。4s 亚层在 3d 之前填充，因为其能量略低。这一模式适用于第一行 d 区元素，尽管常有误解。
5. Hund’s Rule and Pauli Exclusion Principle | 洪特规则与泡利不相容原理
Hund’s rule states that when filling degenerate orbitals (orbitals of the same energy, e.g. three p orbitals), electrons occupy them singly with parallel spins before any pairing occurs. This minimises electron‑electron repulsion and leads to the most stable arrangement.
洪特规则指出，在填充简并轨道（能量相同的轨道，例如三个 p 轨道）时，电子先以平行自旋单独占据各个轨道，然后才会配对。这最大限度地减少了电子之间的排斥，导致最稳定的排列。
Pauli’s exclusion principle says that no two electrons in an atom can have the same set of four quantum numbers. In one orbital, this means a maximum of two electrons with opposite spins, often shown as ↑↓. Together, these rules explain the magnetic properties and the structure of orbital box diagrams.
泡利不相容原理指出，原子中不能有两个电子具有完全相同的一组四个量子数。在一个轨道中，这意味着最多容纳两个自旋相反的电子，通常表示为 ↑↓。这两个规则一起解释了物质的磁性以及轨道箱式图的画法。
6. Electron Configurations of Atoms (Periods 1-4) | 原子电子排布（第1-4周期）
You must be able to write full electron configurations using the s, p, d notation. For Periods 1 to 3, configurations follow regular filling: H: 1s¹; He: 1s²; Li: 1s² 2s¹; Be: 1s² 2s²; B: 1s² 2s² 2p¹; C: 1s² 2s² 2p²; N: 1s² 2s² 2p³; O: 1s² 2s² 2p⁴; F: 1s² 2s² 2p⁵; Ne: 1s² 2s² 2p⁶.
你必须能够用 s, p, d 符号写出完整的电子排布。对于第1至3周期，排布遵循规律填充：H: 1s¹; He: 1s²; Li: 1s² 2s¹; Be: 1s² 2s²; B: 1s² 2s² 2p¹; C: 1s² 2s² 2p²; N: 1s² 2s² 2p³; O: 1s² 2s² 2p⁴; F: 1s² 2s² 2p⁵; Ne: 1s² 2s² 2p⁶。
For Period 4, after argon (1s² 2s² 2p⁶ 3s² 3p⁶), the 4s subshell fills before 3d. Potassium: …4s¹; Calcium: …4s². Then scandium begins filling 3d: Sc: [Ar] 3d¹ 4s²; Ti: [Ar] 3d² 4s²; V: [Ar] 3d³ 4s²; Cr: an exception; Mn: [Ar] 3d⁵ 4s²; Fe: [Ar] 3d⁶ 4s²; Co: [Ar] 3d⁷ 4s²; Ni: [Ar] 3d⁸ 4s²; Cu: exception; Zn: [Ar] 3d¹⁰ 4s².
在第4周期，氩（1s² 2s² 2p⁶ 3s² 3p⁶）之后，4s 亚层在 3d 之前填充。钾：…4s¹；钙：…4s²。然后钪开始填充 3d：Sc: [Ar] 3d¹ 4s²; Ti: [Ar] 3d² 4s²; V: [Ar] 3d³ 4s²; Cr：例外；Mn: [Ar] 3d⁵ 4s²; Fe: [Ar] 3d⁶ 4s²; Co: [Ar] 3d⁷ 4s²; Ni: [Ar] 3d⁸ 4s²; Cu：例外；Zn: [Ar] 3d¹⁰ 4s²。
7. Shorthand Notation and Orbital Diagrams | 简写符号与轨道图
Shorthand electron configuration uses the previous noble gas in brackets to represent the inner electrons. For example, sodium (1s² 2s² 2p⁶ 3s¹) becomes [Ne] 3s¹. For iron, the full configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s², so the shorthand is [Ar] 3d⁶ 4s².
简写电子排布使用括号内的上一个稀有气体来表示内层电子。例如，钠（1s² 2s² 2p⁶ 3s¹）表示为 [Ne] 3s¹。对于铁，完整排布是 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶ 4s²，所以简写为 [Ar] 3d⁶ 4s²。
Orbital box diagrams represent each orbital as a box and electrons as arrows (↑ or ↓). For nitrogen, you would draw three separate p orbital boxes, each with one upward arrow before pairing. These diagrams are often required to illustrate Hund’s rule and to determine the number of unpaired electrons.
轨道箱式图将每个轨道表示为一个方框，电子用箭头（↑ 或 ↓）表示。对于氮，你会画出三个分开的 p 轨道方框，每个方框先放一个朝上的箭头，然后再配对。这些图常用于说明洪特规则和确定未成对电子的数量。
8. Ions: Writing Electron Configurations | 离子：书写电子排布
For positive ions (cations), electrons are removed from the highest energy level first. Even though 4s fills before 3d, when forming ions from transition metals, 4s electrons are lost before 3d. For example, Fe atom: [Ar] 3d⁶ 4s²; Fe²⁺: [Ar] 3d⁶; Fe³⁺: [Ar] 3d⁵.
对于正离子（阳离子），电子首先从最高能级移除。尽管 4s 比 3d 先填充，但在过渡金属形成离子时，4s 电子比 3d 电子先失去。例如，Fe 原子：[Ar] 3d⁶ 4s²；Fe²⁺：[Ar] 3d⁶；Fe³⁺：[Ar] 3d⁵。
For negative ions (anions), electrons are added to the next available orbital. For example, O: 1s² 2s² 2p⁴; O²⁻: 1s² 2s² 2p⁶ (same as neon). Chlorine atom: [Ne] 3s² 3p⁵; Cl⁻: [Ne] 3s² 3p⁶ (isoelectronic with argon). Isoelectronic species have the same electron configuration.
对于负离子（阴离子），电子被添加到下一个可用的轨道。例如，O: 1s² 2s² 2p⁴；O²⁻: 1s² 2s² 2p⁶（与氖相同）。氯原子：[Ne] 3s² 3p⁵；Cl⁻: [Ne] 3s² 3p⁶（与氩等电子）。等电子体具有相同的电子排布。
Exam tip: When deducing the configuration of a transition metal ion, always remove 4s electrons first, then 3d if needed. This is a common pitfall. For Sc³⁺, the configuration is simply [Ar]; the 4s² and the one 3d electron are both removed.
考试提示：在推断过渡金属离子的排布时，总是先移除 4s 电子，必要时再移除 3d 电子。这是一个常见陷阱。对于 Sc³⁺，其排布就是 [Ar]；4s² 和一个 3d 电子都被移除了。
9. Exceptions: Chromium and Copper | 例外：铬和铜
Two major exceptions in Period 4 are chromium (Cr, Z=24) and copper (Cu, Z=29). According to the normal filling order, Cr would be [Ar] 3d⁴ 4s² and Cu would be [Ar] 3d⁹ 4s². However, the actual configurations are [Ar] 3d⁵ 4s¹ and [Ar] 3d¹⁰ 4s¹ respectively.
第4周期有两个重要的例外：铬（Cr, Z=24）和铜（Cu, Z=29）。按照正常的填充顺序，Cr 应为 [Ar] 3d⁴ 4s²，Cu 应为 [Ar] 3d⁹ 4s²。然而，实际的排布分别是 [Ar] 3d⁵ 4s¹ 和 [Ar] 3d¹⁰ 4s¹。
The reason for this stability is that a half‑filled d subshell (d⁵) and a completely filled d subshell (d¹⁰) provide extra stability due to symmetry and exchange energy. By promoting one 4s electron into the 3d subshell, the atom achieves a more stable arrangement.
这种稳定性的原因是，半满 d 亚层（d⁵）和全满 d 亚层（d¹⁰）由于对称性和交换能而带来额外的稳定性。通过将一个 4s 电子激发到 3d 亚层，原子实现了更稳定的排列。
You may be asked to explain these exceptions using the concept of sub‑shell stability. Remember that WJEC expects you to know Cr and Cu specifically. Some exam boards also include Mo and Ag, but for WJEC, focus on Cr and Cu in Period 4.
你可能会被要求用亚层稳定性的概念来解释这些例外。记住，WJEC 期待你特别了解 Cr 和 Cu。有些考试局还包括 Mo 和 Ag，但对于 WJEC，重点放在第4周期的 Cr 和 Cu。
10. Electron Configuration and the Periodic Table | 电子排布与周期表
The periodic table is divided into blocks based on which subshell is being filled: s-block (Groups 1‑2), p-block (Groups 13‑18), d-block (transition metals, Groups 3‑12) and f-block (lanthanides and actinides). The period number corresponds to the highest principal quantum number n of an occupied shell.
周期表根据正在被填充的亚层划分为不同的区：s 区（第1-2族）、p 区（第13-18族）、d 区（过渡金属，第3-12族）和 f 区（镧系元素和锕系元素）。周期数对应于已占据壳层的最高主量子数 n。
For example, elements in Period 3 have their highest energy electrons in n=3 orbitals (3s or 3p). The number of columns in the s-block (2), p-block (6) and d-block (10) directly reflects the maximum electron capacity of those subshells.
例如，第3周期的元素其最高能量电子位于 n=3 轨道（3s 或 3p）。s 区（2列）、p 区（6列）和 d 区（10列）的列数直接反映了这些亚层的最大电子容量。
By knowing an element’s position, you can deduce its electron configuration. For instance, phosphorus is in Group 15, Period 3: [Ne] 3s² 3p³. This link makes electron configuration a powerful predictive tool for chemical behaviour.
知道元素的位置，你就能推断出其电子排布。例如，磷在第15族、第3周期：[Ne] 3s² 3p³。这种联系使电子排布成为预测化学行为的有力工具。
11. Evidence from Ionisation Energies | 电离能的证据
Successive ionisation energies provide direct experimental evidence for electron shells and subshells. A large jump in ionisation energy indicates that an electron is being removed from a shell closer to the nucleus, supporting the idea of principal energy levels.
逐级电离能为电子壳层和亚层的存在提供了直接的实验证据。电离能的巨大跃迁表明电子正在从更靠近原子核的壳层中被移除，这支持了主能级的概念。
For example, aluminium (1s² 2s² 2p⁶ 3s² 3p¹) shows a significant rise between the third and fourth ionisation energies, marking the transition from removing the outer 3p electron to removing a 3s electron. A much larger jump occurs after removing all n=3 electrons, confirming the shell structure.
例如，铝（1s² 2s² 2p⁶ 3s² 3p¹）在第三和第四电离能之间显示出显著的跃升，标志着从移除外层 3p 电子过渡到移除 3s 电子。在移除所有 n=3 电子之后，会出现更大的跃升，证实了壳层结构。
Similarly, the pattern of first ionisation energies across a period reflects the increasing nuclear charge and the stability of half‑filled and fully‑filled subshells. Dips at B, Al, O and S are explained by orbital filling rules and electron repulsion, a topic that often appears in WJEC data analysis questions.
同样，同一周期内第一电离能的变化趋势反映了核电荷的增加以及半满和全满亚层的稳定性。B、Al、O 和 S 处出现的下降可通过轨道填充规则和电子排斥来解释，这个话题经常在 WJEC 的数据分析题中出现。
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
Always write electron configurations in the correct energy order, not numerical order: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶ for iron. Do not reorder 3d before 4s when writing the full configuration. For ions, remove 4s electrons first even though they were filled first.
书写电子排布时，一定要按正确的能量顺序，而不是数字顺序：铁为 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶。不要在全写时将 3d 放在 4s 之前。对于离子，即使 4s 电子先被填充，也要先移除它们。
Avoid confusing the number of orbitals with the number of electrons. When drawing box diagrams, show all degenerate orbitals as separate boxes, apply Hund’s rule and clearly indicate opposing spins. For shorthand, ensure the noble gas core is correct, e.g. [Ar] for elements 18< Z≤36.
避免混淆轨道数量和电子数量。在画箱式图时，将所有简并轨道显示为独立的方框，应用洪特规则，并清楚地标示相反的自旋。简写时要确保所用的稀有气体核心正确，例如对于 18< Z≤36 的元素使用 [Ar]。
Learn the two exceptions, Cr and Cu, and be ready to explain them in terms of d‑subshell stability. Use ionisation energy data to support your answers where applicable. Finally, practise matching configurations to blocks and periods—this is a quick, high‑mark exam skill.
记住两个例外 Cr 和 Cu，并准备好用 d 亚层稳定性来解释它们。在适用时，使用电离能数据来支持你的答案。最后，练习将排布与区、周期对应起来——这是一个快速、得分高的考试技巧。
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