Atomic Structure for A-Level Edexcel Chemistry | A-Level Edexcel 化学：原子结构 考点精讲

📚 Atomic Structure for A-Level Edexcel Chemistry | A-Level Edexcel 化学：原子结构 考点精讲

Atomic structure is a foundational topic in A-Level Chemistry. Understanding the nature of subatomic particles, isotopes, electron configurations, and ionisation energies is essential for explaining chemical bonding, periodicity, and reactivity. This article covers the key concepts required by the Edexcel specification, including mass spectrometry and successive ionisation energies, with bilingual explanations to help you grasp every detail and perform well on exams.

原子结构是A-Level化学的基础课题。理解亚原子粒子的性质、同位素、电子排布和电离能对于解释化学键、周期性和反应性至关重要。本文涵盖Edexcel考纲要求的关键概念，包括质谱法和逐级电离能，并提供中英双语解释，助你掌握每一个细节并在考试中取得好成绩。

1. Subatomic Particles and Their Properties | 亚原子粒子及其性质

Atoms consist of three types of subatomic particles: protons, neutrons, and electrons. Protons and neutrons reside in the nucleus, while electrons move around the nucleus in specific energy levels. The relative mass and charge of these particles are summarised below.

原子由三种亚原子粒子组成：质子、中子和电子。质子和中子位于原子核内，而电子在特定能级上围绕原子核运动。这些粒子的相对质量和电荷总结如下。

The actual mass of a proton is approximately 1.6726 × 10⁻²⁷ kg, and an electron has a mass of about 9.1094 × 10⁻³¹ kg. Because the electron’s mass is negligibly small, atomic mass is essentially concentrated in the nucleus.

质子的实际质量约为1.6726 × 10⁻²⁷ kg，电子质量约为9.1094 × 10⁻³¹ kg。由于电子质量极小，原子质量基本上集中在原子核。

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 and uniquely identifies the element. The mass number (A) is the total number of protons and neutrons. The relationship is given by:

原子序数(Z)是原子核中的质子数，唯一地确定元素种类。质量数(A)是质子和中子的总数。两者关系如下：

A = Z + N (where N = number of neutrons)

A = Z + N （N为中子数）

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. For example, carbon-12 (¹²C) has 6 protons and 6 neutrons, while carbon-14 (¹⁴C) has 6 protons and 8 neutrons. Both are isotopes of carbon.

同位素是同一元素的不同原子，具有相同的质子数但中子数不同。例如，碳-12(¹²C)有6个质子和6个中子，而碳-14(¹⁴C)有6个质子和8个中子。两者都是碳的同位素。

3. Relative Atomic Mass and Isotopic Abundance | 相对原子质量与同位素丰度

Relative atomic mass (Aᵣ) is defined as the weighted mean mass of an atom relative to 1/12th the mass of an atom of carbon-12. It accounts for the masses and relative abundances of all isotopes of an element. The general formula when using percentage abundance is:

相对原子质量(Aᵣ)定义为原子的加权平均质量与一个碳-12原子质量的1/12的比值。它考虑了元素所有同位素的质量和相对丰度。使用百分比丰度时的计算公式为：

Aᵣ = Σ (isotopic mass × % abundance) / 100

For chlorine, the two main isotopes are ³⁵Cl (75% abundance) and ³⁷Cl (25% abundance). Substituting into the formula: Aᵣ = (35 × 75 + 37 × 25) / 100 = 35.5. Hence the relative atomic mass of chlorine is 35.5.

以氯为例，两种主要同位素为³⁵Cl (丰度75%) 和 ³⁷Cl (丰度25%)。代入公式：Aᵣ = (35 × 75 + 37 × 25) / 100 = 35.5。因此氯的相对原子质量为35.5。

4. Mass Spectrometry | 质谱法

Mass spectrometry is a powerful technique used to determine relative atomic masses and isotopic abundances. In a time-of-flight (TOF) mass spectrometer, the sample undergoes five main stages: 1. Ionisation – the sample is bombarded with high-energy electrons (electron impact) or ionised by electrospray; 2. Acceleration – positive ions are accelerated by an electric field to a constant kinetic energy; 3. Ion drift – ions travel through a flight tube, with lighter ions reaching the detector faster; 4. Detection – ions hit an electron multiplier, generating a current proportional to abundance; 5. Data analysis – a mass spectrum is produced showing peaks separated by mass-to-charge ratio (m/z).

质谱法是测定相对原子质量和同位素丰度的重要技术。在飞行时间(TOF)质谱仪中，样品经历五个主要阶段：1. 电离——样品被高能电子轰击（电子轰击电离）或通过电喷雾电离；2. 加速——正离子被电场加速至恒定动能；3. 离子漂移——离子通过飞行管，较轻的离子更快到达检测器；4. 检测——离子撞击电子倍增器，产生与丰度成正比的电流；5. 数据分析——生成质谱图，显示按质荷比(m/z)分离的峰。

In a mass spectrum, the x-axis shows m/z

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