📚 KS3 Cambridge Chemistry: Formula and Theorem Quick Reference Handbook | KS3剑桥化学：公式定理速查手册
This handbook gathers the essential formulas, laws and concepts from the KS3 Cambridge Chemistry syllabus. Use it as a rapid revision tool to reinforce your understanding and boost confidence before tests.
本手册汇集了KS3剑桥化学课程中的核心公式、定律和关键概念。你可以用它进行快速复习，巩固理解，并在考试前增强信心。
1. States of Matter and Particle Theory | 物质状态与粒子理论
The particle model explains the behaviour of solids, liquids and gases. In solids, particles vibrate in fixed positions; in liquids, they are close but can slide past each other; in gases, they are far apart and move rapidly.
粒子模型解释了固体、液体和气体的行为。固体中粒子在固定位置振动；液体中粒子紧挨着，但能相互滑动；气体中粒子相距很远并快速运动。
Changes of state are reversible physical changes. Melting and boiling absorb energy, while freezing and condensing release energy. The melting point and boiling point are characteristic properties of a pure substance.
物态变化是可逆的物理变化。熔化和沸腾吸收能量，而凝固和冷凝释放能量。熔点和沸点是纯物质的特征性质。
Density (ρ) = Mass (m) / Volume (V)
Density is a measure of how much mass is packed into a unit volume. Solids are usually denser than liquids, and gases have very low density.
密度衡量单位体积内所含质量的大小。固体通常比液体密度大，气体密度非常低。
2. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element is a pure substance made of only one type of atom. Each element is represented by a chemical symbol, such as O for oxygen and Fe for iron.
元素是由同一种原子组成的纯净物。每种元素用一个化学符号表示，例如氧用 O 表示，铁用 Fe 表示。
A compound consists of two or more different elements chemically bonded in fixed proportions. The properties of a compound are different from those of its constituent elements.
化合物由两种或多种不同元素按固定比例通过化学键结合而成。化合物的性质与其组成元素的性质截然不同。
A mixture contains different substances that are physically combined, not chemically joined. The composition of a mixture can vary. Air is a mixture, while water is a compound.
混合物含有不同物质，它们只是简单地混合在一起，没有发生化学结合。混合物的组成可以变化。空气是混合物，而水是化合物。
3. Atomic Structure | 原子结构
Atoms consist of a central nucleus surrounded by electrons. The nucleus contains protons with a positive charge and neutrons with no charge. Electrons have a negative charge.
原子由中心的原子核和核外电子构成。原子核内含有带正电荷的质子和不带电的中子。电子带负电荷。
mber of electrons in a neutral atom. Mass number = number of protons + number of neutrons.
关键关系：原子序数 = 质子数 = 中性原子中的电子数。质量数 = 质子数 + 中子数。
Number of neutrons = Mass number - Atomic number
When an atom loses or gains electrons, it becomes an ion. Metals typically form positive ions (cations), while non‑metals form negative ions (anions).
当原子失去或得到电子时，会变成离子。金属通常形成阳离子（正离子），而非金属形成阴离子（负离子）。
4. The Periodic Table | 元素周期表
The modern periodic table arranges elements in order of increasing atomic number. Rows are called periods, and columns are called groups. Elements in the same group have similar chemical properties because they have the same number of outer electrons.
现代周期表按原子序数递增的顺序排列元素。横行称为周期，纵列称为族。同一族的元素化学性质相似，因为它们的原子最外层电子数相同。
Metals are located on the left and centre of the table; non‑metals are on the right. Group 1 metals are the alkali metals, Group 7 elements are the halogens, and Group 0 elements are the noble gases.
金属位于周期表的左侧和中间，非金属位于右侧。第1族是碱金属，第7族是卤素，第0族是稀有气体。
The historical contribution of Dmitri Mendeleev, who left gaps for undiscovered elements, underpins the periodic law that properties recur periodically when elements are arranged by atomic number.
门捷列夫为未发现的元素留下了空位，他的贡献奠定了周期律的基础：当元素按原子序数排列时，其性质呈现周期性变化。
5. Chemical Formulae and Naming | 化学式与命名
Compounds are named by combining the names of the elements present. For a simple ionic compound, the metal is named first, followed by the non‑metal with its ending changed to ‘‑ide’, e.g. sodium chloride.
化合物的命名是将所含元素的名称组合起来。对于简单的离子化合物，先写金属名称，再写非金属名称并将词尾改为‘‑化某’，如氯化钠。
To write a correct chemical formula, the total positive charge must balance the total negative charge. Charges of common ions: Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Cl⁻, O²⁻, SO₄²⁻.
书写正确的化学式时，正负电荷必须相互平衡。常见离子所带电荷：Na⁺, K⁺, Mg²⁺, Ca²⁺, Al³⁺, Cl⁻, O²⁻, SO₄²⁻。
Formula of aluminium oxide: Al₂O₃ (2 × Al³⁺ + 3 × O²⁻)
The numerical subscripts in a formula show the smallest whole number ratio of ions in the compound.
化学式中的下角标数字表示化合物中各种离子的最简整数比。
6. Writing Chemical Equations | 书写化学方程式
e. Reactants are written on the left and products on the right, separated by an arrow (→).
化学方程式用符号和化学式描述化学反应。反应物写在左边，生成物写在右边，中间用箭头（→）连接。
The Law of Conservation of Mass states that matter cannot be created or destroyed in a chemical reaction. Therefore, the total mass of reactants equals the total mass of products, and the number of atoms of each element must be the same on both sides of the equation.
质量守恒定律指出，在化学反应中物质既不能被创造也不能被消灭。因此，反应物的总质量等于生成物的总质量，而且方程式两边各元素的原子数目必须相等。
2Mg + O₂ → 2MgO (balanced equation)
Balancing is done by placing coefficients in front of formulae; never change the subscripts inside a formula.
配平时在化学式前面加上系数；切勿改变化学式内部的下标。
7. Types of Chemical Reactions | 化学反应类型
Many reactions fall into predictable patterns. Combination (synthesis) reactions form a single product from two or more reactants. Decomposition breaks a compound into simpler substances.
许多反应遵循可预测的规律。化合反应由两种或多种反应物生成一种产物。分解反应将化合物分解成更简单的物质。
Displacement occurs when a more reactive element replaces a less reactive one in a compound. Neutralisation is a specific double displacement between an acid and a base producing salt and water.
当较活泼的元素从化合物中置换出较不活泼的元素时，发生置换反应。中和反应是酸与碱之间的特殊复分解反应，生成盐和水。
Metal + Acid → Salt + Hydrogen
Acid + Alkali → Salt + Water
These general equations help predict products when the reactants are known.
这些通式有助于在已知反应物的情况下预测产物。
8. Acids and Alkalis | 酸与碱
Acids release hydrogen ions (H⁺) in water; alkalis release hydroxide ions (OH⁻) in water. The pH scale measures the concentration of H⁺ ions, ranging from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral.
酸在水中释放氢离子（H⁺），碱在水中释放氢氧根离子（OH⁻）。pH标度用于衡量H⁺离子的浓度，范围从0（强酸性）到14（强碱性），7为中性。
Indicators such as litmus change colour in acidic or alkaline solutions. Universal indicator gives a range of colours corresponding to pH.
指示剂（如石蕊）在酸性或碱性溶液中会变色。通用指示剂能呈现与pH值对应的多种颜色。
H⁺(aq) + OH⁻(aq) → H₂O(l) (Neutralisation)
In neutralisation, an acid and an alkali react to form a salt and water only. The ionic equation above represents the essential change.
在中和反应中，酸和碱反应只生成盐和水。上面的离子方程式代表了反应的本质变化。
9. Reactivity Series | 金属活动性顺序
The reactivity series lists metals in order of decreasing reactivity. A more reactive metal displaces a less reactive metal from its compound.
金属活动性顺序按反应活泼性由高到低排列。较活泼的金属能把较不活泼的金属从它的化合物中置换出来。
Common order (partial): K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Hg, Ag, Au. Potassium is the most reactive; gold is the least.
常见顺序（部分）：钾、钠、钙、镁、铝、锌、铁、锡、铅、（氢）、铜、汞、银、金。钾最活泼，金最不活泼。
Metals above hydrogen react with acids to produce hydrogen gas. Metals above carbon must be extracted from their ores by electrolysis rather than reduction with carbon.
位于氢前的金属能与酸反应产生氢气。位于碳前的金属必须用电解法而不是用碳还原法从矿石中提取。
10. Rates of Reaction | 反应速率
The rate of a chemical reaction measures how quickly reactants are used up or products are formed. It can be changed by several factors.
化学反应速率衡量反应物消耗或产物生成的快慢。它受多种因素影响。
Increasing temperature increases the energy and frequency of collisions. Higher concentration or pressure increases the number of particles in a given volume. Larger surface area exposes more reactant particles to collisions. A catalyst provides an alternative pathway with lower activation energy without being used up.
升高温度会增加碰撞的能量和频率。增大浓度或压强增加了给定体积中的粒子数。增大表面积使更多反应物粒子参与碰撞。催化剂提供了一条活化能较低的替代路径，自身在反应中不被消耗。
Rate ∝ frequency of effective collisions
The collision theory states that for a reaction to occur, particles must collide with sufficient energy and the correct orientation.
碰撞理论指出，要发生反应，粒子必须发生碰撞，且碰撞需有足够的能量和正确的取向。
11. Exothermic and Endothermic Reactions | 放热与吸热反应
An exothermic reaction transfers energy from the reacting system to the surroundings, causing a temperature rise. Combustion, respiration and neutralisation are exothermic.
放热反应将能量从反应体系传递到周围环境，导致温度升高。燃烧、呼吸作用和中和反应都是放热反应。
An endothermic reaction takes in energy from the surroundings, so the temperature drops. Photosynthesis and dissolving ammonium nitrate in water are endothermic processes.
吸热反应从周围环境吸收能量，因此温度下降。光合作用以及硝酸铵溶于水是吸热过程。
Chemical bonds must be broken (endothermic step) and new bonds formed (exothermic step). The overall energy change determines whether the reaction is net exothermic or endothermic.
化学反应需要断裂化学键（吸热步骤）并形成新化学键（放热步骤）。总体的能量变化决定了反应是净放热还是净吸热。
12. Key Calculations | 关键计算
Relative atomic mass (Aᵣ) compares the average mass of an atom of an element to 1/12 the mass of a carbon‑12 atom. It has no units.
相对原子质量（Aᵣ）是将某元素的一个原子的平均质量与碳‑12原子质量的1/12相比较，没有单位。
elative atomic masses of all atoms in the formula. For water, H₂O: Mᵣ = (2 × 1) + 16 = 18.
化合物的相对式量（Mᵣ）是化学式中所有原子的相对原子质量之和。例如水 H₂O：Mᵣ = (2×1) + 16 = 18。
% mass of element = (Number of atoms × Aᵣ of element ÷ Mᵣ of compound) × 100
This formula helps calculate the percentage by mass of each element in a compound.
这个公式用于计算化合物中各元素的质量百分比。
Density calculations also appear: ρ = m/V. Always ensure units match – mass in grams (g) and volume in cm³, or mass in kilograms (kg) and volume in m³.
还要用到密度计算：ρ = m/V。要注意单位的匹配：质量单位用克（g），体积用立方厘米（cm³）；或质量用千克（kg），体积用立方米（m³）。
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