📚 Atomic Structure and Electron Configuration for AS Chemistry | AS化学：原子结构与电子排布
Understanding atomic structure is the foundation of AS Chemistry. It explains how atoms behave, how they bond, and why elements show periodic trends. This article covers the key ideas in the OxfordAQA International AS Chemistry specification, including subatomic particles, isotopes, electron arrangement, and ionisation energy.
理解原子结构是 AS 化学的基础。它解释了原子的行为方式、成键原因以及元素呈现周期性变化规律的原因。本文涵盖 OxfordAQA International AS 化学大纲中的核心内容，包括亚原子粒子、同位素、电子排布和电离能。
1. The Nuclear Atom and Subatomic Particles | 原子核模型与亚原子粒子
Atoms consist of a small, dense central nucleus containing protons and neutrons, surrounded by electrons arranged in energy levels. Protons carry a relative charge of +1, neutrons are electrically neutral, and electrons carry a relative charge of -1.
原子由一个致密的小型中心原子核以及核外电子组成。原子核内含有质子和中子，核外电子按能级排布。质子相对电荷为 +1，中子不带电，电子相对电荷为 -1。
eans almost all the mass of an atom is concentrated in the nucleus, while the electrons occupy most of the volume.
这些粒子的相对质量约为：质子 = 1，中子 = 1，电子 = 1/1836。这意味着原子几乎全部质量集中在原子核内，而电子占据了原子绝大部分体积。
| Particle | 粒子 | Relative charge | 相对电荷 | Relative mass | 相对质量 | Position | 位置 |
|---|---|---|---|
| Proton | 质子 | +1 | 1 | Nucleus | 原子核 |
| Neutron | 中子 | 0 | 1 | Nucleus | 原子核 |
| Electron | 电子 | -1 | 1/1836 | Energy levels | 能级 |
2. Atomic Number, Mass Number, and Isotopes | 原子序数、质量数与同位素
The atomic number (Z) is the number of protons in the nucleus of an atom. It defines the element and also equals the number of electrons in a neutral atom. The mass number (A) is the total number of protons and neutrons in the nucleus.
原子序数 (Z) 是原子核中的质子数。它决定了元素的种类，对于中性原子，它也等于电子数。质量数 (A) 是原子核中质子和中子的总数。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They have identical chemical properties because chemical behaviour depends on electrons, but their physical properties such as mass may differ.
同位素是同一元素中质子数相同而中子数不同的原子。由于化学性质取决于电子，同位素的化学性质相同，但质量等物理性质可能不同。
For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. They all have 6 protons but contain 6, 7, and 8 neutrons respectively.
例如，碳有三种天然同位素：碳-12、碳-13 和碳-14。它们都有 6 个质子，但分别含有 6、7 和 8 个中子。
3. Relative Atomic Mass and Mass Spectrometry | 相对原子质量与质谱法
Relative atomic mass (Aᵣ) is the weighted mean mass of an atom of an element compared with 1/12 of the mass of an atom of carbon-12. Since most elements exist as mixtures of isotopes, Aᵣ is calculated using the percentage abundances of each isotope.
相对原子质量 (Aᵣ) 是指某元素一个原子的加权平均质量与碳-12 原子质量的 1/12 之比。由于大多数元素以同位素混合物形式存在，Aᵣ 需要根据各同位素的百分比丰度进行计算。
The formula used in calculations is:
计算中使用的公式为：
Aᵣ = Σ (isotopic mass × percentage abundance) / 100
A mass spectrometer provides evidence for isotopes by generating a mass spectrum. The peak positions give isotopic masses, and the peak heights give relative abundances.
质谱仪通过产生质谱图为同位素提供证据。谱峰位置表示同位素质量，谱峰高度表示相对丰度。
For example, chlorine has two main isotopes: ³⁵Cl and ³⁷Cl with abundances of about 75% and 25%. Its relative atomic mass is therefore approximately:
例如，氯有两种主要同位素：³⁵Cl 和 ³⁷Cl，丰度分别约为 75% 和 25%。因此其相对原子质量约为：
Aᵣ(Cl) = (35 × 75 + 37 × 25) / 100 = 35.5
4. Electron Shells and Subshells | 电子层与亚层
umber n = 1, 2, 3, 4, and so on. The number of electrons a shell can hold is given by 2n².
电子围绕原子核分层排布。每个电子层具有主量子数 n = 1、2、3、4 等。一个电子层最多可容纳的电子数为 2n²。
Shells are divided into subshells called s, p, d, and f. The first shell has only an s subshell, the second shell has s and p subshells, and the third shell has s, p, and d subshells.
电子层又分为 s、p、d、f 等亚层。第一层只有 s 亚层，第二层有 s 和 p 亚层，第三层有 s、p 和 d 亚层。
- 1st shell: 1s, holds up to 2 electrons | 第一层：1s，最多容纳 2 个电子
- 2nd shell: 2s, 2p, holds up to 8 electrons | 第二层：2s、2p，最多容纳 8 个电子
- 3rd shell: 3s, 3p, 3d, holds up to 18 electrons | 第三层：3s、3p、3d，最多容纳 18 个电子
- 4th shell: 4s, 4p, 4d, 4f, holds up to 32 electrons | 第四层：4s、4p、4d、4f，最多容纳 32 个电子
5. Atomic Orbitals and Electron Spin | 原子轨道与电子自旋
An orbital is a region of space around the nucleus where there is a high probability of finding an electron. Each orbital can hold a maximum of two electrons, and these electrons must have opposite spins.
原子轨道是原子核外空间中的一个区域，电子在该区域出现的概率很高。每个轨道最多可容纳两个电子，而且这两个电子必须自旋方向相反。
The s subshell contains 1 orbital, the p subshell contains 3 orbitals, the d subshell contains 5 orbitals, and the f subshell contains 7 orbitals. Therefore, an s subshell holds 2 electrons, a p subshell holds 6 electrons, a d subshell holds 10 electrons, and an f subshell holds 14 electrons.
s 亚层包含 1 个轨道，p 亚层包含 3 个轨道，d 亚层包含 5 个轨道，f 亚层包含 7 个轨道。因此，s 亚层最多容纳 2 个电子，p 亚层最多容纳 6 个电子，d 亚层最多容纳 10 个电子，f 亚层最多容纳 14 个电子。
Within a p subshell, the three orbitals are labelled pₓ, pᵧ, and pz. They are arranged at right angles to one another. Electrons fill the orbitals singly before pairing up, in line with Hund's rule.
在 p 亚层中，三个轨道分别标记为 pₓ、pᵧ 和 pz。它们彼此垂直排列。根据洪特规则，电子先以单个方式填入轨道，然后才进行配对。
6. Writing Electron Configurations | 电子排布式的书写
Electron configurations show how electrons are distributed among shells and subshells. The notation uses numbers to indicate the shell, letters for the subshell, and superscripts for the number of electrons.
电子排布式表示电子在各个电子层和亚层中的分布情况。书写时用数字表示电子层，用字母表示亚层，用上标数字表示电子数。
ectron configuration of oxygen (Z = 8) is 1s² 2s² 2p⁴. Sodium (Z = 11) is 1s² 2s² 2p⁶ 3s¹.
例如，氧原子 (Z = 8) 的电子排布式为 1s² 2s² 2p⁴。钠原子 (Z = 11) 的电子排布式为 1s² 2s² 2p⁶ 3s¹。
(Z = 20) is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s², and scandium (Z = 21) is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s².
对于第四周期的元素，4s 亚层先于 3d 亚层被填充。例如，钙 (Z = 20) 的电子排布式为 1s² 2s² 2p⁶ 3s² 3p⁶ 4s²，钪 (Z = 21) 为 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹ 4s²。
¹⁰ 4s¹. These arise because half-filled and fully filled d subshells give extra stability.
铬和铜是例外。铬 (Z = 24) 的电子排布式为 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹，铜 (Z = 29) 为 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹。这是因为半充满和全充满的 d 亚层具有额外的稳定性。
Ions are formed by removing or adding electrons. For transition metals, electrons are removed from the 4s subshell before the 3d subshell.
离子通过失去或得到电子形成。对于过渡金属，电子先从 4s 亚层失去，然后才从 3d 亚层失去。
7. First Ionisation Energy: Definition and Trends | 第一电离能：定义与变化趋势
First ionisation energy is the energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous ions with a single positive charge.
第一电离能是指从一摩尔气态原子中移走一摩尔电子，生成一摩尔带一个单位正电荷的气态离子所需要的能量。
The equation for the first ionisation energy of an element X is:
元素 X 的第一电离能方程式为：
X(g) → X⁺(g) + e⁻
Ionisation energy is always endothermic because energy must be supplied to overcome the attraction between the negative electron and the positive nucleus.
电离能始终是吸热过程，因为必须提供能量来克服负电子与正原子核之间的吸引力。
Across a period, first ionisation energy generally increases. This is because nuclear charge increases, while shielding remains similar, so the outer electrons are held more tightly.
同一周期从左到右，第一电离能总体呈增大趋势。这是因为核电荷增加，而屏蔽作用基本不变，因此外层电子被原子核吸引得更强。
Down a group, first ionisation energy decreases because the outer electrons are further from the nucleus and experience greater shielding, making them easier to remove.
同一族从上到下，第一电离能减小，因为外层电子距离原子核更远，屏蔽作用增强，电子更容易被移走。
8. Successive Ionisation Energies and Evidence for Shells | 逐级电离能与电子层证据
Successive ionisation energies refer to the energy needed to remove each subsequent electron from a gaseous ion. For example, the second ionisation energy is:
逐级电离能是指从气态离子中逐个移走电子所需的能量。例如，第二电离能方程式为：
X⁺(g) → X²⁺(g) + e⁻
Successive ionisation energies always increase because as electrons are removed, the same nuclear charge attracts fewer electrons, and the ion becomes more positively charged. The remaining electrons are held more strongly.
逐级电离能依次增大，因为随着电子被移走，相同核电荷吸引更少的电子，离子正电荷增多，剩余电子被束缚得更强。
Large jumps in successive ionisation energies provide evidence for electron shells. A big jump occurs when an electron is removed from a new inner shell that is much closer to the nucleus and less shielded.
逐级电离能中的大幅跃升为电子层的存在提供了证据。当电子从一个更靠近原子核且屏蔽更少的新内层被移走时，会出现大幅跃升。
For sodium, the first ionisation energy is relatively low, but the second ionisation energy is much higher. This shows that the first electron is removed from the 3s subshell, while the second electron is removed from the more tightly held 2p subshell.
对于钠，第一电离能相对较低，而第二电离能则高得多。这说明第一个电子从 3s 亚层移走，而第二个电子从被束缚得更紧的 2p 亚层移走。
9. Exam-Style Application and Common Pitfalls | 考试题型与常见误区
AS exam questions often ask you to define ionisation energy, write electron configurations, explain trends, and use mass spectra to calculate relative atomic mass. It is important to include state symbols in definitions and equations.
AS 考试常见题型包括定义电离能、书写电子排布式、解释变化趋势，以及利用质谱图计算相对原子质量。书写定义和方程式时务必包含状态符号。
A common mistake is to say that ionisation energy is the energy to remove an electron from an atom, without specifying that the atom is gaseous and that one mole is involved. The definition must be precise.
一个常见误区是简单地说电离能是从原子移走一个电子的能量，而未说明原子处于气态且涉及一摩尔。定义必须准确完整。
Another common error is writing the electron configuration of ions incorrectly. Remember that for transition metals, 4s electrons are removed before 3d electrons. For example, the electron configuration of Fe²⁺ is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶, not 3d⁸.
另一个常见错误是离子电子排布式书写不正确。记住，对于过渡金属，4s 电子先于 3d 电子失去。例如，Fe²⁺ 的电子排布式为 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁶，而不是 3d⁸。
When explaining periodicity in ionisation energy, always refer to nuclear charge, shielding, and distance of the outer electron from the nucleus. Use these three factors to build a precise argument.
在解释电离能的周期性变化时，始终要从核电荷、屏蔽作用和外层电子与核的距离三个方面进行说明，并用这三个因素构建准确的论证。
Finally, when calculating relative atomic mass from mass spectra, always divide by the total abundance, not by the number of peaks. Leaving out the abundance denominator is a frequent error.
最后，根据质谱图计算相对原子质量时，务必除以总丰度，而不是除以谱峰数量。漏掉丰度分母是一个常见错误。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图