📚 SQA Year 9 Chemistry Formulae & Theorems Quick Reference Handbook | SQA Year 9 化学：公式定理速查手册
Welcome to your go-to quick reference for essential chemistry formulae and theorems covered in the SQA Year 9 curriculum. This handbook condenses key concepts—from atomic structure and mole calculations to reaction rates and acid-base chemistry—into clear, bilingual explanations. Use it to reinforce your understanding and boost your exam confidence.
欢迎使用这份针对SQA Year 9化学课程的基本公式与定理速查手册。本手册将原子结构、摩尔计算、反应速率以及酸碱化学等关键概念浓缩为清晰的双语解释，帮助你巩固理解，提升考试信心。
1. Atomic Structure & Relative Atomic Mass | 原子结构与相对原子质量
Atoms are composed of protons, neutrons and electrons. The relative atomic mass (Ar) of an element is the average mass of its atoms compared to 1/12 the mass of a carbon‑12 atom. It is calculated as: Ar = sum of (isotope mass × % abundance) / 100.
原子由质子、中子和电子组成。元素的相对原子质量（Ar）是其原子平均质量与碳‑12原子质量的1/12的比值。计算公式为：Ar = Σ（同位素质量 × 丰度%）/ 100。
The atomic number (Z) equals the number of protons, and the mass number (A) equals the sum of protons and neutrons. In a neutral atom, the number of electrons equals the number of protons.
原子序数（Z）等于质子数，质量数（A）等于质子数与中子数之和。在中性原子中，电子数等于质子数。
2. Writing Chemical Formulae | 化学式的书写
Chemical formulae show the types and ratios of atoms in a compound. For ionic compounds, the total positive charge must balance the total negative charge. For example, sodium chloride is NaCl because Na⁺ and Cl⁻ combine in a 1:1 ratio. Magnesium oxide is MgO because Mg²⁺ and O²⁻ balance. For covalent compounds, prefixes like mono‑, di‑ are sometimes used, e.g., CO₂ for carbon dioxide.
化学式表示化合物中原子的种类和数量比。对于离子化合物，总正电荷必须与总负电荷平衡。例如，氯化钠为NaCl，因为Na⁺和Cl⁻以1:1结合。氧化镁为MgO，因为Mg²⁺与O²⁻电荷平衡。共价化合物有时使用前缀如一、二，例如CO₂为二氧化碳。
When a polyatomic ion like hydroxide (OH⁻) appears more than once, parentheses are used, e.g., Ca(OH)₂ for calcium hydroxide, indicating two OH⁻ ions per Ca²⁺.
当多原子离子（如氢氧根OH⁻）出现超过一次时，需使用括号，例如Ca(OH)₂表示氢氧化钙，每个Ca²⁺对应两个OH⁻。
3. Balancing Equations & Law of Conservation of Mass | 化学方程式的配平与质量守恒定律
The law of conservation of mass states that atoms are neither created nor destroyed in a chemical reaction. Therefore, the total mass of reactants equals the total mass of products. To satisfy this law, chemical equations must be balanced by adjusting coefficients so that each element has the same number of atoms on both sides.
质量守恒定律指出，化学反应中原子既不会凭空产生也不会凭空消失。因此，反应物的总质量等于生成物的总质量。为满足这一定律，必须通过调整化学计量系数来配平化学方程式，使每种元素的原子总数在两边相等。
bustion of methane: CH₄ + 2O₂ → CO₂ + 2H₂O. There are 1 C, 4 H and 4 O atoms on each side.
例如，甲烷的燃烧：CH₄ + 2O₂ → CO₂ + 2H₂O。两边分别有1个碳原子、4个氢原子和4个氧原子。
4. Formula Mass & Relative Molecular Mass | 式量与相对分子质量
The relative formula mass (Mr) for an ionic compound, or relative molecular mass for covalent substances, is the sum of the relative atomic masses of all atoms in the formula. It is unitless but numerically corresponds to the molar mass in g/mol.
相对式量（离子化合物）或相对分子质量（共价物质）是化学式中所有原子相对原子质量的总和。它没有单位，但在数值上等于摩尔质量（g/mol）。
Calculate Mr of H₂SO₄: (2×1) + (32) + (4×16) = 98. So the molar mass is 98 g/mol.
计算H₂SO₄的Mr：(2×1) + (32) + (4×16) = 98。因此摩尔质量为98 g/mol。
5. The Mole Concept & Mass-Mole Conversion | 摩尔概念与质量-摩尔转换
The mole (mol) is the SI unit for amount of substance. One mole contains 6.02 × 10²³
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