📚 KS3 AQA Chemistry: Formula & Theorem Quick Reference Handbook | KS3 AQA 化学：公式定理速查手册
This quick reference guide brings together all the essential chemical formulae, laws, and principles you need for KS3 AQA Chemistry. From conservation of mass to writing balanced equations, from particle models to pH scales, these key concepts form the foundation of your chemistry study. Use this handbook to review definitions, check equations, and solidify your understanding before exams and practical work.
本速查手册汇集了KS3 AQA化学课程中所有必需的化学式、定律和原理。从质量守恒到书写配平方程式，从粒子模型到pH标尺，这些关键概念构成了你化学学习的基础。使用本手册复习定义、检查方程式，并在考试和实验前巩固你的理解。
1. Law of Conservation of Mass | 质量守恒定律
In all chemical reactions, the total mass of the reactants is always equal to the total mass of the products. No atoms are created or destroyed; they are only rearranged. This means the mass you measure before a reaction should be exactly the same as the mass after, provided no gas escapes or enters the system.
Total mass of reactants = Total mass of products
在所有化学反应中，反应物的总质量总是等于生成物的总质量。原子不会被创造或消失，只会重新排列。这意味着在封闭系统中，反应前测得的质量与反应后的质量完全一致，前提是没有气体逸出或进入。
2. Relative Atomic Mass and Relative Formula Mass | 相对原子质量与相对式量
on the periodic table. Relative formula mass (Mᵣ) is the sum of the Aᵣ values of all atoms in a chemical formula. For example, Mᵣ of H₂O = (2 × Aᵣ of H) + (1 × Aᵣ of O) ≈ (2 × 1) + 16 = 18.
Aᵣ = average mass of one atom ÷ (1/12 × mass of one ¹²C atom)
Mᵣ = Σ (Aᵣ of each atom in the formula)
相对原子质量（Aᵣ）是元素的一个原子的平均质量与一个碳-12原子（¹²C）质量的1/12的比值，无单位，你可以在元素周期表上找到它。相对式量（Mᵣ）是化学式中所有原子Aᵣ的总和。例如，H₂O的Mᵣ = (2 × H的Aᵣ) + (1 × O的Aᵣ) ≈ (2 × 1) + 16 = 18。
3. Writing Chemical Formulae: Ions and Ionic Compounds | 离子化合物的化学式书写规则
Ionic compounds are made of positive ions (cations) and negative ions (anions). The overall charge must be zero, so you combine ions in a ratio that balances the charges. For example, sodium chloride: Na⁺ and Cl⁻ give NaCl. Magnesium chloride: Mg²⁺ and Cl⁻ give MgCl₂ — the numerical charges are swapped to become subscripts, and then simplified if needed. The table below lists common ions you will need to build formulae.
| Ion name | Formula | Charge |
|---|---|---|
| Sodium | Na⁺ | +1 |
| Potassium | K⁺ | +1 |
| Calcium | Ca²⁺ | +2 |
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