A-Level Chemistry: Atomic and Molecular Mass Calculations | A-Level 化学：原子与分子质量的计算

📚 A-Level Chemistry: Atomic and Molecular Mass Calculations | A-Level 化学：原子与分子质量的计算

Atomic and molecular mass calculations are the foundation of quantitative chemistry. In the CIE A-Level Chemistry syllabus, students are expected to calculate relative atomic mass (Aᵣ), relative molecular mass (Mᵣ), and relative formula mass from data such as isotopic abundances, and to apply these concepts to mole-based calculations involving mass, Avogadro’s constant, and particle numbers. Mastery of this topic unlocks most of the stoichiometry problems you will encounter in the exam.

原子与分子质量的计算是定量化学的基础。在 CIE A-Level 化学大纲中，学生需要能够根据同位素丰度等数据计算相对原子质量（Aᵣ）、相对分子质量（Mᵣ）和相对式量，并将这些概念应用于涉及质量、阿伏伽德罗常数和粒子数的摩尔计算。掌握这一主题，便能解决考试中遇到的大部分化学计量问题。

1. Relative Atomic Mass (Aᵣ) | 相对原子质量（Aᵣ）

The relative atomic mass (Aᵣ) of an element is defined as the weighted mean mass of one atom of that element compared with one-twelfth of the mass of one atom of carbon-12. Carbon-12 was chosen as the standard because it is a stable, abundant isotope that allows precise measurements in mass spectrometry.

元素的相对原子质量（Aᵣ）定义为：该元素一个原子的平均质量与碳-12 一个原子质量的十二分之一之比。选择碳-12 作为标准，是因为它是一种稳定且丰度较高的同位素，便于质谱法中的精确测量。

Aᵣ = (average mass of one atom of the element) ÷ (1/12 × mass of one