📚 AQA 9620 International A-level Chemistry Specimen 2016 Unit 1 Q2: Mass Spectrometry and Relative Atomic Mass | AQA 9620 国际 A-level 化学 2016 年样卷第 1 单元第 2 题：质谱与相对原子质量
This revision page works through the style and skills tested by Question 2 of the AQA 9620 International A-level Chemistry Unit 1 specimen paper (2016). The question focuses on mass spectrometry, isotopes and the calculation of relative atomic mass, with links to electronic structure and ionisation energy.
本复习页围绕 AQA 9620 国际 A-level 化学第 1 单元 2016 年样卷第 2 题的命题风格与考点展开。该题重点考查质谱、同位素以及相对原子质量的计算，并联系电子排布与电离能。
1. What Question 2 Is Testing | 第 2 题考查什么
In the 2016 AQA 9620 Unit 1 specimen paper, Question 2 is built around a mass spectrum. It tests whether you can define relative atomic mass, identify isotopes, read peak abundances from a spectrum, and calculate an average atomic mass.
在 2016 年 AQA 9620 第 1 单元样卷中，第 2 题以质谱图为主线，考查相对原子质量的定义、同位素的识别、从谱图中读取峰丰度以及计算平均原子质量的能力。
You should expect 4-6 marks, often split as 1 definition mark, 2-3 calculation marks and 1-2 explanation marks.
该题通常占 4-6 分，一般包括 1 个定义分、2-3 个计算分和 1-2 个解释分。
2. Isotopes and Nuclear Symbols | 同位素与核素符号
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They therefore have the same atomic number but different mass numbers.
同位素是同一元素质子数相同而中子数不同的原子。它们的原子序数相同，但质量数不同。
For example, magnesium has three stable isotopes: ²⁴Mg, ²⁵Mg and ²⁶Mg. The superscript is the mass number, equal to protons plus neutrons.
例如，镁有三种稳定同位素：²⁴Mg、²⁵Mg 和 ²⁶Mg。上标是质量数，等于质子数加中子数。
- ²⁴Mg: 12 protons and 12 neutrons.
- ²⁵Mg: 12 protons and 13 neutrons.
- ²⁶Mg: 12 protons and 14 neutrons.
- ²⁴Mg：12 个质子和 12 个中子。
- ²⁵Mg：12 个质子和 13 个中子。
- ²⁶Mg：12 个质子和 14 个中子。
3. Mass Spectrometer Ionisation | 质谱仪中的电离
In the time-of-flight mass spectrometer used by AQA, a sample is ionised by electron impact or electrospray. In Unit 1 questions, electron impact is common: high-energy electrons knock one electron out of each atom to form a positive ion.
在 AQA 使用的飞行时间质谱仪中，样品通过电子轰击或电喷雾进行电离。第 1 单元题目常用电子轰击：高能电子从每个原子上打出一个电子，形成正离子。
M + e⁻ → M⁺ + 2e⁻
Here M is the atom and M⁺ is the positive ion that enters the electric field.
式中 M 是原子，M⁺ 是进入电场的正离子。
4. Acceleration, Deflection and Detection | 加速、偏转与检测
Positive ions are accelerated by an electric field so that they all have the same kinetic energy. They then pass through a flight tube and are detected, with lighter ions arriving faster than heavier ions.
正离子在电场中加速，使它们具有相同的动能。离子随后穿过飞行管并被检测，质量较小的离子比较重的离子到达更快。
The mass-to-charge ratio, m/z, is used to label the x-axis of a mass spectrum. For singly charged ions, m/z equals the mass number.
质谱
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