Electron Configuration: Key Exam Points | 电子排布考点精讲

📚 Electron Configuration: Key Exam Points | 电子排布考点精讲

Understanding electron configuration is fundamental to mastering chemistry. It explains how electrons are arranged in atomic orbitals, which determines an element’s chemical properties, reactivity, and bonding behaviour. For IB and OCR examinations, a solid grasp of the principles, notation, exceptions, and trends is essential.

理解电子排布是掌握化学的基础。它解释了电子在原子轨道中的排列方式，决定了元素的化学性质、反应活性和成键行为。对于IB和OCR考试，牢固掌握其原理、表示法、例外情况和趋势至关重要。

1. Energy Levels and Sublevels | 能级与亚层

Electrons occupy specific energy levels, designated by the principal quantum number n (n = 1, 2, 3, …). Each energy level contains one or more sublevels: s, p, d, and f. The number of sublevels in a given energy level equals n. For example, n=1 has only 1s; n=2 has 2s and 2p; n=3 has 3s, 3p, and 3d, and so on.

电子占据特定的能级，用主量子数 n 表示（n = 1, 2, 3, …）。每个能级包含一个或多个亚层：s、p、d 和 f。亚层的数目等于 n。例如，n=1 只有 1s 亚层；n=2 有 2s 和 2p；n=3 有 3s、3p 和 3d，依此类推。

Each sublevel contains a fixed number of orbitals. An s sublevel has 1 orbital, p has 3, d has 5, and f has 7. Each orbital can hold a maximum of two electrons. Therefore, s sublevel holds up to 2 electrons, p up to 6, d up to 10, and f up to 14.

每个亚层包含固定数量的轨道。s 亚层有 1 个轨道，p 有 3 个，d 有 5 个，f 有 7 个。每个轨道最多可容纳两个电子。因此，s 亚层最多容纳 2 个电子，p 最多 6 个，d 最多 10 个，f 最多 14 个。

2. Orbitals and Their Shapes | 轨道与形状

An atomic orbital is a region of space around the nucleus where there is a high probability of finding an electron. Each orbital type has a distinctive shape. s orbitals are spherical, p orbitals are dumbbell-shaped (or figure-eight) with three orientations (pₓ, pᵧ, p₂), and d orbitals have more complex shapes, including cloverleaf patterns.

原子轨道是原子核周围电子出现概率较高的空间区域。每种轨道类型有独特的形状。s 轨道为球形，p 轨道为哑铃形（或纺锤形），具有三个取向（pₓ、pᵧ、p₂），d 轨道形状更复杂，包括四叶草形等。

It’s important to be able to sketch orbital shapes for exams, particularly s and p orbitals. Understanding orbital shapes helps explain molecular geometry and hybridization later.

考试中要求能够画出轨道形状草图，尤其是 s 和 p 轨道。理解轨道形状有助于以后解释分子几何构型和杂化。

3. The Aufbau Principle | 构造原理

The Aufbau principle states that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. The order of filling is not simply by principal quantum number n. For example, the 4s sublevel is filled before the 3d sublevel because 4s is lower in energy for neutral atoms of potassium and calcium. The general filling order is: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p. A useful mnemonic is to follow the diagonal rule or build from the periodic table.

构造原理指出，电子优先填充能量最低的原子轨道，然后再占据较高能级。填充顺序并非简单地按主量子数 n 增加。例如，4s 亚层先于 3d 亚层填充，因为对于钾和钙的中性原子，4s 的能量低于 3d。一般填充顺序为：1s、2s、2p、3s、3p、4s、3d、4p、5s、4d、5p、6s、4f、5d、6p、7s、5f、6d、7p。可利用对角线规则或借助周期表来记忆。

4. 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 four quantum numbers. In a single orbital, this means that the two electrons must have opposite spins, represented as ↑ and ↓. Consequently, an orbital can hold a maximum of two electrons, and they must be paired with opposite spins.

泡利不相容原理指出，原子中不可能有两个电子具有完全相同的四个量子数。在同一个轨道中，这意味着两个电子必须自旋相反，通常用 ↑ 和 ↓ 表示。因此，一个轨道最多容纳两个电子，并且它们必定是自旋配对的。

5. Hund’s Rule of Maximum Multiplicity | 洪特规则

Hund’s rule states that electrons will fill orbitals of the same energy (degenerate orbitals, such as the three p orbitals) singly, with parallel spins, before any pairing occurs. This arrangement minimises electron-electron repulsion and gives the atom the lowest energy configuration. For example, in a p³ configuration, all three electrons occupy separate p orbitals with parallel spins (↑ ↑ ↑), not paired (↑↓ ↑ _).

洪特规则指出，电子在填充简并轨道（如三个能量相等的 p 轨道）时，会尽可能以自旋平行的方式单独占据，然后才进行配对。这种排布方式使电子间排斥力最小，原子能量最低。例如，p³ 构型中，三个电子分别占据三个 p 轨道，且自旋平行（↑ ↑ ↑），而不是先配对（↑↓ ↑ _）。

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

To write the full electron configuration of an atom, determine the atomic number Z, then assign electrons to sublevels following the filling order, respecting the maximum capacities. Use superscripts to indicate the number of electrons in each sublevel, e.g., carbon (Z=6): 1s² 2s² 2p². For longer configurations, separate sublevels with spaces. Common convention writes the configuration in order of increasing principal quantum number, even though 4s fills before 3d.

书写原子的完整电子排布式，首先确定原子序数 Z，然后按填充顺序将电子分配到各亚层，并遵守最大容量。用上标表示各亚层的电子数，例如碳（Z=6）：1s² 2s² 2p²。对于较长的排布式，亚层之间用空格分隔。通常习惯按主量子数递增的顺序书写，尽管 4s 先于 3d 填充。

For transition metals, the configuration is often written with the 3d sublevel filled after 4s, but many exam boards accept writing the sublevels in order of n, e.g., for Fe (Z=26): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, which is perfectly fine. However, for ions, the 4s electrons are removed first because they are the outermost, even though 4s was filled before 3d.

对于过渡金属，通常按 n 排序书写，例如，铁（Z=26）可写作 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶，考试中通常接受这种写法。但对于离子，4s 电子最先失去，因为它们是外层电子，尽管填充时 4s 在先。

7. Orbital Box Diagrams | 轨道填充图

Orbital box diagrams (or orbital diagrams) use boxes or lines to represent orbitals,

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