📚 Year 9 WJEC Chemistry: Formula & Theorem Quick Reference | 九年级 WJEC 化学：公式定理速查手册
This handbook brings together the most important formulas, theorems, and key concepts from the Year 9 WJEC Chemistry curriculum. Each entry is presented with a clear statement followed by concise explanations in both English and Chinese, making it perfect for quick revision. The topics cover atomic structure, chemical calculations, states of matter, acids and bases, energy changes, reaction rates, and more.
本手册汇集了九年级 WJEC 化学课程中最重要的公式、定理和核心概念。每个条目都先给出明确陈述，再附上简明扼要的中英文解释，非常适合快速复习。内容涵盖原子结构、化学计算、物态变化、酸与碱、能量变化、反应速率等主题。
1. Atomic Structure | 原子结构
A = Z + N
The mass number (A) is the total number of protons and neutrons in the nucleus. The atomic number (Z) is the number of protons, which determines the element. The number of neutrons (N) can be found by subtracting Z from A.
质量数 (A) 是原子核中质子与中子的总数。原子序数 (Z) 是质子数，决定了元素的种类。中子数 (N) 可通过 A 减去 Z 求得。
Charge = Z − number of e⁻
For ions, the charge is the difference between the number of protons and the number of electrons. A positive charge indicates the atom has lost electrons; a negative charge means it has gained electrons.
对于离子，电荷等于质子数与电子数之差。正电荷表示原子失去了电子，负电荷表示原子得到了电子。
Electron shells: 2, 8, 8 ...
Electrons occupy shells around the nucleus. The first shell holds up to 2 electrons, the second and third shells hold up to 8 electrons each (for the first 20 elements). The arrangement is written as a sequence, e.g., 2,8,1 for sodium.
电子按壳层排布在原子核外。第一层最多容纳2个电子，第二层和第三层最多容纳8个电子（前20号元素）。这种排布以数字序列表示，例如钠的电子排布是 2,8,1。
2. Chemical Bonds and Formulae | 化学键与化学式
Total positive charge = Total negative charge
In an ionic compound, the total positive charge from cations must equal the total negative charge from anions, so the overall compound is neutral. For example, magnesium chloride is MgCl₂ because one Mg²⁺ ion balances with two Cl⁻ ions.
在离子化合物中，阳离子所带的正电荷总数必须等于阴离子所带的负电荷总数，使整个化合物呈电中性。例如氯化镁的化学式为 MgCl₂，因为一个 Mg²⁺ 离子与两个 Cl⁻ 离子电荷平衡。
Covalent bond = shared pair of electrons
A covalent bond forms when two atoms share a pair of electrons. Each shared pair represents one covalent bond, and atoms can share multiple pairs to form double or triple bonds.
当两个原子共用一对电子时，就形成了共价键。每一对共用电子代表一个共价键，原子可以通过共用多对电子形成双键或三键。
Molecular formula ↔ atom count
A molecular formula shows the exact number of each type of atom in a molecule. For instance, H₂O reveals two hydrogen atoms and one oxygen atom per water molecule.
分子式表示一个分子中每种原子的实际数目。例如 H₂O 表明一个水分子含有两个氢原子和一个氧原子。
3. Relative Masses (Aᵣ and Mᵣ) | 相对原子质量与相对式量
Aᵣ = average mass of atom ÷ (1/12 mass of carbon‑12 atom)
Relative atomic mass (Aᵣ) compares the average mass of an element's atoms to 1/12 of the mass of a carbon‑12 atom. It has no units. The Aᵣ values are found on the Periodic Table.
相对原子质量 (Aᵣ) 是元素的原子平均质量与一个碳‑12 原子质量的 1/12 之比值，没有单位。Aᵣ 值可在元素周期表中查到。
Mᵣ = Σ (number of atoms × Aᵣ)
atoms in the formula. For example, H₂O: Mᵣ = (2×1) + 16 = 18. For ionic compounds the term "relative formula mass" is used.
相对式量 (Mᵣ) 是化学式中所有原子的相对原子质量的总和。例如 H₂O：Mᵣ = (2×1) + 16 = 18。对于离子化合物，通常使用“相对式量”这一术语。
4. The Mole and Avogadro's Constant | 摩尔与阿伏伽德罗常数
n = m / M
The number of moles (n) is calculated by dividing the mass of a substance (m, in grams) by its molar mass (M, in g/mol). The molar mass is numerically equal to the Aᵣ or Mᵣ.
摩尔数 (n) 等于物质的质量（m，单位克）除以它的摩尔质量（M，单位 g/mol）。摩尔质量的数值与 Aᵣ 或 Mᵣ 相同。
N = n × Nₐ
particles (N) in a sample can be found by multiplying the number of moles (n) by Avogadro' ol⁻¹). This constant is the number of atoms, molecules or ions in one mole of a substance.
样品中的粒子总数 (N) 等于摩尔数 (n) 乘以阿伏伽德罗常数 (Nₐ = 6.02 × 10²³ mol⁻¹)。该常数是 1 摩尔物质所含的原子、分子或离子的数目。
5. Chemical Equations and Stoichiometry | 化学方程式与化学计量
Mass of reactants = Mass of products
The Law of Conservation of Mass states that atoms cannot be created or destroyed in a chemical reaction. The total mass of the reactants is always equal to the total mass of the products.
质量守恒定律指出，在化学反应中原子既不会凭空产生也不会消失。反应物的总质量总是等于生成物的总质量。
Balancing rule: same number of each atom on both sides
To balance an equation, place large numbers (coefficients) in front of the formulas so that the number of atoms of each element is the same on the reactant and product sides. Subscripts in formulas must not be changed.
配平方程式时，在化学式前添加适当的系数，使得每一种元素的原子个数在反应物和生成物两边相等。化学式中的下标不能改变。
Mole ratio = coefficient ratio
ts. For example, 2H₂ + O₂ → 2H₂O means 2 mol H₂ reacts with 1 mol O₂ to produce 2 mol H₂O.
配平方程式中的系数比等于物质的摩尔数之比。例如，2H₂ + O₂ → 2H₂O 表示 2 mol H₂ 与 1 mol O₂ 反应生成 2 mol H₂O。
6. States of Matter and Gas Volume | 物态与气体体积
V(gas) = n × 24 dm³ (at RTP)
At room temperature and pressure (RTP, about 20 °C and 1 atm), one mole of any gas occupies approximately 24 dm³. This is the molar volume. The volume (in dm³) of a gas can be calculated by multiplying the number of moles by 24.
在常温常压下（RTP，约 20 °C 和 1 atm），1 摩尔任何气体的体积约为 24 dm³，这就是气体的摩尔体积。气体体积（单位 dm³）等于摩尔数乘以 24。
Avogadro's law: equal volumes, equal molecules
Equal volumes of all gases, under the same conditions of temperature and pressure, contain the same number of molecules. This follows directly from Avogadro's law.
在相同的温度和压强下，体积相等的任何气体都含有相同数目的分子，这是阿伏伽德罗定律的直接推论。
7. Solution Concentration | 溶液浓度
Published by TutorHao | Year 9 Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图