Atomic Structure and Electron Configuration Essentials | 原子结构与核外电子排布要点

📚 Atomic Structure and Electron Configuration Essentials | 原子结构与核外电子排布要点

Atomic structure lies at the heart of chemistry, explaining how protons, neutrons and electrons organise to form matter. Understanding electron configuration is essential for predicting reactivity, periodic trends and bonding behaviour.

原子结构是化学的核心，它解释了质子、中子和电子如何组织形成物质。理解核外电子排布对于预测反应活性、周期性规律和成键行为至关重要。

1. Subatomic Particles and the Nucleus | 亚原子粒子与原子核

An atom consists of a dense, positive nucleus surrounded by negative electrons. The three main subatomic particles are the proton, neutron and electron, with relative masses and charges summarised below.

原子由一个致密的正电原子核和周围带负电的电子组成。三种主要亚原子粒子是质子、中子和电子，其相对质量和电荷汇总如下。

Particle	Relative Mass	Relative Charge
Proton	1	+1
Neutron	1	0
Electron	1/1836	−1

The atomic number Z equals the number of protons, while the mass number A equals the sum of protons and neutrons. In a neutral atom, the number of electrons equals Z.

原子序数 Z 等于质子数，质量数 A 等于质子数与中子数之和。在电中性原子中，电子数等于 Z。

2. Orbitals and Quantum Numbers | 轨道与量子数

Electrons are described by four quantum numbers. The principal quantum number n defines the energy level; the azimuthal quantum number l defines the subshell (s, p, d, f); the magnetic quantum number mₗ defines the orbital orientation; and the spin quantum number mₛ has values +½ or −½.

电子由四个量子数描述。主量子数 n 定义能层；角量子数 l 定义亚层（s、p、d、f）；磁量子数 mₗ 定义轨道取向；自旋量子数 mₛ 取值为 +½ 或 −½。

l = 0 → s; l = 1 → p; l = 2 → d; l = 3 → f

The number of orbitals in a subshell is 2l+1, and each orbital can hold at most two electrons with opposite spins.

亚层中轨道数为 2l+1，每个轨道最多容纳两个自旋相反的电子。

3. Shells and Subshells: Energy Order | 能层、亚层与能量顺序

For hydrogen-like atoms, subshell energies depend only on n. For multi-electron atoms, electron-electron repulsion raises the energy of higher-l subshells, producing the familiar Aufbau order.

对于类氢原子，亚层能量只取决于 n。对于多电子原子，电子间排斥作用使高 l 亚层能量升高，产生熟悉的构造原理顺序。

1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s

Remember that 4s fills before 3d, but when ionising transition metals, electrons are removed first from 4s, then from 3d.

记住先填充 4s 再填充 3d，但电离过渡金属时，先失去 4s 电子，再失去 3d 电子。

4. Aufbau Principle | 构造原理

The Aufbau principle states that electrons occupy the lowest available energy orbitals first. This provides a systematic method for writing ground-state electron configurations.

构造原理指出，电子优先占据能量最低的可用轨道。这为书写基态电子排布提供了系统方法。

For example, oxygen (Z=8) fills 1s, 2s and 2p in sequence.

例如，氧（Z=8）依次填充 1s、2s 和 2p。

O: 1s² 2s² 2p⁴

This order can be obtained from the diagonal rule or from an energy-level diagram.

这一顺序可通过对角线规则或能级图获得。

5. 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. Consequently, an orbital holds at most two electrons, and they must have opposite spins.

泡利不相容原理指出：同一原子中，任何两个电子的四个量子数不能完全相同。因此，一个轨道最多容纳两个电子，且它们的自旋必须相反。

If two electrons share the same orbital, they are written as ↑↓. A box diagram with two arrows pointing in opposite directions represents a filled orbital.

如果两个电子共用同一轨道，写作 ↑↓。用两个方向相反的箭头表示成对电子的方框图，代表一个填满的轨道。

6. Hund’s Rule | 洪特规则

Hund’s rule states that when degenerate orbitals are available, electrons occupy them singly with parallel spins before pairing occurs. This minimises electron-electron repulsion.

洪特规则指出：当有简并轨道时，电子先以相同自旋分占各轨道，然后才配对。这可使电子间排斥最小化。

For carbon (Z=6), the 2p subshell has three orbitals. The two 2p electrons occupy separate p-orbitals with parallel spins:

对于碳（Z=6），2p 亚层有三个轨道。两个 2p 电子分占不同的 p 轨道且自旋平行：

2p: ↑ ↑ (not ↑↓ )

This explains why the ground-state configuration of nitrogen is 1s² 2s² 2p³ with three unpaired electrons.

这解释了为什么氮的基态排布是 1s² 2s² 2p³，且有三个未成对电子。

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

Using the Aufbau order and the rules above, we can write full configurations. For potassium (Z=19), the electron configuration is:

利用构造原理和上述规则，我们可以写出完整排布式。对于钾（Z=19），其电子排布为：

K: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

For chromium (Z=24) and copper (Z=29), there are exceptions due to extra stability from half-filled and fully-filled d subshells.

对于铬（Z=24）和铜（Z=29），由于半充满和全充满 d 亚层具有额外稳定性而出现例外。

Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

8. Core Notation and Valence Electrons | 核心简写与价电子

To shorten configurations, the noble-gas core is replaced by its symbol in square brackets. For example, sodium can be written as [Ne] 3s¹.

为了简化排布式，用方括号内稀有气体符号表示内层电子核心。例如钠可写作 [Ne] 3s¹。

Valence electrons are the electrons in the outermost shell that participate in chemical bonding. For main-group elements, the group number often equals the number of valence electrons.

价电子是最外层壳层中参与化学成键的电子。对于主族元素，族序数通常等于价电子数。

Li: [He] 2s¹ → 1 valence electron

锂：[He] 2s¹ → 1 个价电子
O: [He] 2s² 2p⁴ → 6 valence electrons

氧：[He] 2s² 2p⁴ → 6 个价电子

9. Orbital Box Diagrams | 轨道表示式

Orbital box diagrams show each orbital as a box and each electron as an arrow. They clearly display pairing and unpaired electrons. For nitrogen:

轨道表示式用方框表示轨道、箭头表示电子，能清晰显示成对和未成对电子。以氮为例：

1s: ↑↓ 2s: ↑↓ 2p: ↑ ↑ ↑

This diagram immediately shows three unpaired electrons in the 2p subshell, matching nitrogen’s paramagnetic behaviour.

该图立即显示 2p 亚层有三个未成对电子，与氮的顺磁性行为一致。

10. Exceptions and Ionisation | 例外情况与电离

Beyond chromium and copper, other exceptions occur in the 4d and 5d transition series, such as niobium (Nb), molybdenum (Mo) and platinum (Pt). These arise from the similar energies of (n−1)d and ns orbitals.

除铬和铜外，4d 和 5d 过渡系还有其他例外，如铌（Nb）、钼（Mo）和铂（Pt）。这些来源于 (n−1)d 与 ns 轨道能量接近。

When forming cations, electrons are removed from the highest energy level first. For iron (Fe: [Ar] 3d⁶ 4s²), the Fe²⁺ ion is [Ar] 3d⁶ and Fe³⁺ is [Ar] 3d⁵.

形成阳离子时，先失去最高能层电子。对于铁（Fe: [Ar] 3d⁶ 4s²），Fe²⁺ 为 [Ar] 3d⁶，Fe³⁺ 为 [Ar] 3d⁵。

11. Periodic Table Connections | 与元素周期表的联系

Electron configuration determines the position of an element in the periodic table. The block (s, p, d, f) corresponds to the last occupied subshell, while the period number equals the principal quantum number of the valence shell.

电子排布决定了元素在周期表中的位置。元素所在区（s、p、d、f）对应最后一个填充的亚层，周期数等于价电子层的主量子数。

Group 1 (alkali metals): ns¹

第 1 族（碱金属）：ns¹
Group 17 (halogens): ns² np⁵

第 17 族（卤素）：ns² np⁵
Transition metals: (n−1)d¹⁻¹⁰ ns¹⁻²

过渡金属：(n−1)d¹⁻¹⁰ ns¹⁻²

These patterns explain trends in ionisation energy, atomic radius and electronegativity.

这些规律解释了电离能、原子半径和电负性的周期性变化。

12. Worked Example and Common Mistakes | 例题与常见错误

Write the full electron configuration for the sulfide ion S²⁻. Sulfur (Z=16) gains two electrons to reach [Ne] 3s² 3p⁶, which is the same as argon.

写出硫离子 S²⁻ 的完整电子排布。硫（Z=16）得到两个电子后变为 [Ne] 3s² 3p⁶，与氩相同。

S²⁻: 1s² 2s² 2p⁶ 3s² 3p⁶ or [Ar]

Common mistakes include writing 3d before 3p, pairing electrons in a p-subshell before filling all three orbitals, and forgetting that 4s is filled before 3d but emptied before 3d when ionising.

常见错误包括：把 3d 写在 3p 之前；在填满三个 p 轨道之前就配对；忘记 4s 先于 3d 填充，但在电离时先于 3d 失去。

Always check the total number of electrons by summing the superscripts. This simple verification prevents many errors.

务必通过求和上标来检查电子总数。这个简单验证可以避免许多错误。

Published by TutorHao | 化学 Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）

Atomic Structure and Electron Configuration Essentials | 原子结构与核外电子排布要点