Electron Configuration | 电子排布

📚 Electron Configuration | 电子排布

Understanding electron configuration is central to A-Level Edexcel Chemistry. It explains not only the position of an element in the periodic table but also its chemical reactivity, bonding behaviour and physical properties. This article covers the core principles, from energy levels and orbitals to the exceptions of chromium and copper, always linking back to ionisation energy evidence.

理解电子排布是 A-Level Edexcel 化学的核心。它不仅解释了元素在周期表中的位置，也说明了元素的化学反应性、成键行为和物理性质。本文涵盖从能级和轨道到铬和铜的特例等核心原理，并始终与电离能的证据相联系。

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

Electrons in an atom occupy principal energy levels (n = 1, 2, 3, 4 …), often called shells. Each principal level contains one or more sub-shells: s, p, d and f. The number of sub-shells in a given principal level equals n. For example, n = 1 has only an s sub-shell, n = 2 has s and p, while n = 3 has s, p and d sub-shells.

原子中的电子占据主能级（n = 1, 2, 3, 4 …），通常称为电子层。每个主能级包含一个或多个亚层：s、p、d 和 f。给定主能级中亚层的数目等于 n。例如，n = 1 只有一个 s 亚层，n = 2 有 s 和 p，而 n = 3 有 s、p 和 d 亚层。

The energy of a sub-shell increases with n and also depends on the sub-shell type. Within the same principal level, the order of increasing energy is s < p < d < f. However, for higher n, the 3d sub-shell is slightly higher in energy than 4s, a fact that leads to the familiar filling order.

亚层的能量随 n 增加而升高，也取决于亚层类型。在同一主能级内，能量递增顺序为 s < p < d < f。然而，对于较高的 n，3d 亚层的能量略高于 4s，这一事实导致了我们所熟知的填充顺序。

2. Orbitals and Orbital Shapes | 轨道与轨道形状

Each sub-shell is made up of orbitals. An orbital is a region of space around the nucleus where there is a high probability (typically 95%) of finding an electron. An s sub-shell has 1 orbital, a p sub-shell has 3 orbitals, a d sub-shell has 5, and an f sub-shell has 7 orbitals.

每个亚层由轨道组成。轨道是原子核周围空间中电子出现概率很高（通常为 95%）的区域。s 亚层有 1 个轨道，p 亚层有 3 个轨道，d 亚层有 5 个，f 亚层有 7 个轨道。

Sub-shell	Number of orbitals	Maximum electrons
s	1	2
p	3	6
d	5	10
f	7	14

s orbitals are spherical. p orbitals are dumbbell-shaped, orientated along the x, y and z axes (pₓ, pᵧ, p₂). d orbitals have more complex shapes, often described as four-leaf clovers (with the exception of the d₂² orbital, which has a doughnut-shaped ring around a lobe). Understanding orbital shapes helps to visualise how atoms bond and why molecules adopt particular geometries.

s 轨道是球形的。p 轨道呈哑铃形，分别沿着 x、y 和 z 轴取向（pₓ、pᵧ、p₂）。d 轨道形状更复杂，常被描述为四叶草形（除了 d₂² 轨道，它在一个瓣周围有一个甜甜圈状的环）。理解轨道形状有助于直观想象原子如何成键以及分子为何采取特定的几何构型。

3. The Aufbau Principle: Filling Order | 能量最低原理：填充顺序

Aufbau means ‘building up’ in German. Electrons fill atomic orbitals in order of increasing energy: the lowest energy orbitals are occupied first. The sequence is often remembered using a diagonal diagram or by following the periodic table. The actual order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

Aufbau 在德语中意为“构建”。电子按能量递增的顺序填充原子轨道：能量最低的轨道最先被占据。这个顺序通常可以通过对角线图记忆，或沿周期表顺序得出。实际顺序是：1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p。

Note the position of 4s before 3d. Although the 4s orbital is further from the nucleus, its energy is slightly lower than that of 3d for neutral atoms of the first transition series, because of a balance between nuclear attraction and electron shielding. This leads to 4s filling before 3d, but interestingly, 4s electrons are also lost before 3d when transition metals form positive ions.

注意 4s 排在 3d 之前。尽管 4s 轨道离核更远，但对于第一过渡系的中性原子，其能量略低于 3d，这是核吸引与电子屏蔽之间平衡的结果。这就使得 4s 先于 3d 填充，但有趣的是，当过渡金属形成正离子时，也是 4s 电子先于 3d 失去。

4. Pauli Exclusion Principle and Hund’s Rule | 泡利不相容原理与洪特规则

The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers. In practice, this means an orbital can hold a maximum of two electrons, and these must have opposite spins (spin-up and spin-down, often represented as ↑ and ↓).

泡利不相容原理指出，原子中没有两个电子可以拥有完全相同的四个量子数。实际上，这意味着一个轨道最多容纳两个电子，并且这两个电子必须自旋相反（自旋向上和自旋向下，通常用 ↑ 和 ↓ 表示）。

Hund’s Rule of Maximum Multiplicity says that when electrons fill a set of degenerate orbitals (orbitals of the same energy, such as three p orbitals or five d orbitals), one electron occupies each orbital singly, with parallel spins, before any orbital is doubly occupied. This minimises electron-electron repulsion and gives the atom greater stability.

洪特最大多重度规则指出，当电子填充一组简并轨道（能量相同的轨道，例如三个 p 轨道或五个 d 轨道）时，电子先以自旋平行的方式单独占据每个轨道，然后才会在任一轨道中配对。这最大程度地减小了电子-电子排斥，使原子更稳定。

For example, a nitrogen atom (Z = 7) has the ground-state configuration 1s² 2s² 2p³. In the 2p sub-shell, the three electrons occupy the three 2p orbitals singly with parallel spins: ↑ ↑ ↑. This can be shown in an orbital box diagram.

例如，氮原子（Z = 7）的基态电子排布为 1s² 2s² 2p³。在 2p 亚层中，三个电子以自旋平行的方式单独占据三个 2p 轨道：↑ ↑ ↑。这可以用轨道方框图来表示。

5. Writing Electron Configurations: Full and Shorthand | 电子排布的书写：完整与简写

Full electron configurations list every occupied sub-shell with a superscript indicating the number of electrons, e.g. sodium (Na, Z = 11): 1s² 2s² 2p⁶ 3s¹. For larger atoms, this becomes lengthy, so noble gas shorthand notation is used. The previous noble gas is written in square brackets followed by the remaining configuration, e.g. chlorine (Cl, Z = 17): [Ne] 3s² 3p⁵.

完整电子排布列出所有被占据的亚层，并用上标标出电子数，例如钠（Na，Z = 11）：1s² 2s² 2p⁶ 3s¹。对较大的原子而言，这样写会变得冗长，因此常使用稀有气体简写表示法。用方括号写出前一周期的稀有气体，再跟上剩余的排布，如氯（Cl，Z = 17）：[Ne] 3s² 3p⁵。

For transition metals, e.g. iron (Fe, Z = 26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, or [Ar] 4s² 3d⁶. Notice that the 4s sub-shell is written before 3d when filling, but some textbooks place 3d before 4s in the shorthand to group the d electrons. Edexcel typically accepts both [Ar] 4s² 3d⁶ and [Ar] 3d⁶ 4s², but be consistent with the order of filling for the full version.

对于过渡金属，例如铁（Fe，Z = 26）：1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶，或 [Ar] 4s² 3d⁶。注意在填充时 4s 亚层写在 3d 之前，但有些教材在简写中将 3d 写在 4s 之前以便将 d 电子放在一起。Edexcel 通常接受 [Ar] 4s² 3d⁶ 和 [Ar] 3d⁶ 4s² 两种写法，但在完整排布中应保持与填充顺序一致。

6. Electron Configurations of Ions | 离子的电子排布

When atoms form positive ions, electrons are removed from the outermost shell with the highest principal quantum number n. For transition metals, this means that 4s electrons are lost before 3d electrons, even though 4s was filled first. For example, Fe²⁺: [Ar] 3d⁶ (not [Ar] 4s² 3d⁴). Fe³⁺: [Ar] 3d⁵.

当原子形成正离子时，电子从主量子数 n 最大的最外层失去。对于过渡金属，这意味着 4s 电子在 3d 电子之前失去，尽管 4s 先填充。例如，Fe²⁺：[Ar] 3d⁶（而不是 [Ar] 4s² 3d⁴）。Fe³⁺：[Ar] 3d⁵。

Negative ions gain electrons into the lowest energy available orbitals. For example, O²⁻: 1s² 2s² 2p⁶, which is isoelectronic with neon. When writing the configuration of an ion, always follow the aufbau order for the neutral atom first, then add or remove electrons according to the charge, using the principle that the highest n electrons are removed first for cations.

负离子则将电子填入能量最低的可用轨道。例如，O²⁻：1s² 2s² 2p⁶，与氖等电子。在书写离子的排布时，总是先按构造原理写出中性原子的排布，再根据电荷加减电子，对阳离子而言，先移去 n 最大的电子。

7. Exceptions: Chromium and Copper | 特例：铬和铜

Two elements in Period 4 have electron configurations that deviate from the aufbau prediction because of the extra stability associated with half-filled and fully filled d sub-shells. Chromium (Cr, Z = 24) has [Ar] 4s¹ 3d⁵, not [Ar] 4s² 3d⁴. Copper (Cu, Z = 29) has [Ar] 4s¹ 3d¹⁰, not [Ar] 4s² 3d⁹.

第四周期中有两种元素的电子排布偏离了构造原理的预测，这是因为半满和全满 d 亚层具有额外的稳定性。铬（Cr，Z = 24）的排布为 [Ar] 4s¹ 3d⁵，而非 [Ar] 4s² 3d⁴。铜（Cu，Z = 29）的排布为 [Ar] 4s¹ 3d¹⁰，而非 [Ar] 4s² 3d⁹。

The explanation is based on energetics: a symmetrical distribution of electrons in a half-filled 3d⁵ set or a fully filled 3d¹⁰ set lowers the overall energy of the atom compared with having a full 4s² and an asymmetric 3d subshell. The energy difference is small but significant enough to be observed experimentally, for instance by magnetic measurements and ionisation energies.

解释基于能量学：与全满 4s² 和不对称 3d 亚层相比，半满 3d⁵ 或全满 3d¹⁰ 组态的电子对称分布降低了原子的总能量。能量差虽小，但足够显著，可以通过磁测量和电离能的实验数据观察到。

There are a few other exceptions (e.g. molybdenum, silver, gold), but the Edexcel specification focuses on chromium and copper. Be sure you can write both the predicted and actual configurations and explain the stability in terms of sub-shell symmetry.

还有一些其他的例外（如钼、银、金），但 Edexcel 考纲重点集中在铬和铜。务必能够写出预测排布和实际排布，并从亚层对称性的角度解释其稳定性。

8. Electron Configuration and the Periodic Table | 电子排布与周期表

The periodic table is structured around electron configurations. The s-block (Groups 1 and 2) corresponds to filling of the outer ns orbital. The p-block (Groups 13 to 18) corresponds to filling of the outer np orbitals. The d-block (transition metals) corresponds to filling of the (n-1)d orbitals. The f-block (lanthanides and actinides) corresponds to filling of the (n-2)f orbitals.

周期表的结构基于电子排布。s 区（第 1 和第 2 族）对应最外层 ns 轨道的填充。p 区（第 13 至 18 族）对应最外层 np 轨道的填充。d 区（过渡金属）对应 (n-1)d 轨道的填充。f 区（镧系和锕系）对应 (n-2)f 轨道的填充。

The period number tells you the highest principal energy level being occupied. The group number for s-block and p-block elements (using the 1-18 system) can be linked directly to the number of outer-shell electrons. For example, aluminium (Group 13) has the outer configuration 3s² 3p¹, giving three outer electrons. This explains the trends in chemical properties across a period and down a group.

周期号告诉你正在占据的最高主能级。s 区和 p 区元素（使用 1-18 族体系）的族号可以直接与最外层电子数相联系。例如，铝（第 13 族）的最外层排布为 3s² 3p¹，共有三个最外层电子。这就解释了同周期和同族元素化学性质的递变规律。

9. Ionisation Energy Evidence for Electron Configuration | 电离能作为电子排布的证据

Successive ionisation energies provide strong experimental support for the shell and sub-shell model. A large jump in ionisation energy indicates the removal of an electron from an inner shell, which is closer to the nucleus and less shielded. For example, the successive ionisation energies of sodium (in kJ mol⁻¹) are: 496, 4563, 6913, 9544, 13352, 16611, 20115, 25491, 28934, 141362. The enormous jump from the first to the second ionisation energy shows that the first electron comes from the outer 3s orbital, while the second electron is removed from the much more tightly held 2p subshell.

逐级电离能为电子层和亚层模型提供了强有力的实验证据。电离能的大幅跃升表明电子是从更内层、更靠近原子核且屏蔽更小的电子层中移去的。例如，钠的逐级电离能（单位 kJ mol⁻¹）为：496, 4563, 6913, 9544, 13352, 16611, 20115, 25491, 28934, 141362。第一与第二电离能之间的巨大跃升表明第一个电子来自外层的 3s 轨道，而第二个电子则从结合得更紧密的 2p 亚层中移去。

Similarly, small jumps within a subshell can be explained by the loss of electrons from the same sub-shell but with increasing effective nuclear charge as electrons are removed. The pattern also confirms the aufbau order: for example, the first ionisation energy of aluminium (3p¹) is lower than that of magnesium (3s²), providing evidence for the higher energy of the 3p orbital compared with 3s.

同样，亚层内电离能之间较小的跃升可以通过从同一亚层失去电子来解释，但随着电子被移除，有效核电荷增加。电离能的模式也证实了构造原理的顺序：例如，铝（3p¹）的第一电离能低于镁（3s²），这为 3p 轨道比 3s 轨道能量更高提供了证据。

10. Linking Electron Configuration to Chemical Properties | 电子排布与化学性质的联系

The reactivity of an element is largely determined by its outer electron configuration. s-block metals such as sodium and calcium are highly reactive reducing agents because they easily lose their outer s electrons. p-block non-metals tend to gain electrons to complete their p subshell, while noble gases with full s²p⁶ configurations are inert.

元素的反应活性主要由其最外层电子排布决定。像钠和钙这样的 s 区金属是强还原剂，因为它们容易失去外层 s 电子。p 区非金属倾向于获得电子以完成其 p 亚层，而具有 s²p⁶ 全满构型的稀有气体则是惰性的。

Transition metals exhibit variable oxidation states because the 3d and 4s electrons are close in energy, allowing different numbers of electrons to be lost. For instance, manganese can show oxidation states from +2 to +7, corresponding to the loss of different combinations of 4s and 3d electrons. This variability is a direct consequence of the d-orbital filling and the small energy gap between sub-shells.

过渡金属表现出可变的氧化态，因为 3d 和 4s 电子的能量相近，允许失去不同数目的电子。例如，锰可以显示从 +2 到 +7 的氧化态，对应于 4s 和 3d 电子的不同组合的失去。这种可变性是 d 轨道填充以及亚层之间能隙较小的直接结果。

Colour in transition metal complexes also arises from d-d electron transitions between split d orbitals, a process that depends intimately on the d electron configuration. A deep understanding of electron configuration therefore underpins much of the inorganic and physical chemistry in the A-Level course.

过渡金属配合物的颜色也源于分裂 d 轨道之间的 d-d 电子跃迁，这一过程与 d 电子排布密切相关。因此，对电子排布的深入理解是 A-Level 课程中许多无机和物理化学内容的基础。

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Electron Configuration | 电子排布