KS3 Edexcel Chemistry Quick-Reference Formula and Theorem Handbook | KS3 Edexcel 化学：公式定理速查手册

📚 KS3 Edexcel Chemistry Quick-Reference Formula and Theorem Handbook | KS3 Edexcel 化学：公式定理速查手册

This handbook provides a concise summary of essential formulas, laws, and key concepts for KS3 Edexcel Chemistry. Use it to review particle theory, atomic structure, chemical equations, acids and alkalis, reactivity, rates, and energy changes. Keep it handy for quick revision before exams.

本手册为 KS3 Edexcel 化学中的核心公式、定律和关键概念提供了简明总结。可用它复习粒子理论、原子结构、化学方程式、酸与碱、反应性、反应速率和能量变化。考前速查，轻松备考。

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1. Particle Theory and States of Matter | 粒子理论与物质状态

The particle model states that all substances are made of tiny particles that are constantly moving. In solids, particles are tightly packed in a regular arrangement and vibrate in fixed positions. In liquids, particles are close together but can slide past each other. In gases, particles are far apart and move rapidly in all directions.

粒子模型指出所有物质都由不断运动的微小粒子组成。固体中，粒子紧密有规律地排列，在固定位置振动；液体中，粒子相距较近但能相互滑动；气体中，粒子相距很远，向各个方向高速运动。

During a change of state, such as melting or boiling, the temperature remains constant even though energy is being transferred. This energy breaks or weakens the forces between particles rather than raising the temperature.

在状态变化过程中（如融化或沸腾），即使能量在转移，温度依然保持不变。这些能量用于打破或削弱粒子间的作用力，而不是升高温度。

The main changes of state are: melting (solid → liquid), boiling/evaporation (liquid → gas), condensing (gas → liquid), freezing (liquid → solid), sublimation (solid → gas) and deposition (gas → solid).

主要的状态变化包括：融化（固→液）、沸腾/蒸发（液→气）、冷凝（气→液）、凝固（液→固）、升华（固→气）和凝华（气→固）。

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2. Atomic Structure and Key Formulas | 原子结构与关键公式

An atom consists of a small central nucleus containing protons and neutrons, surrounded by electrons orbiting in shells. Protons carry a positive charge (+1), electrons carry a negative charge (−1), and neutrons have no charge.

原子由一个包含质子和中子的微小中心原子核以及分层排布的核外电子组成。质子带一个单位正电荷（+1），电子带一个单位负电荷（−1），中子不带电。

The atomic number (Z) is the number of protons in the nucleus. In a neutral atom, the number of electrons equals the atomic number. The mass number (A) is the total number of protons and neutrons.

原子序数（Z）等于原子核中的质子数。在中性原子中，电子数等于原子序数。质量数（A）是质子数与中子数之和。

The number of neutrons can be found by subtracting the atomic number from the mass number.

中子数可以通过质量数减去原子序数求得。

Number of neutrons = A − Z

中子数 = A − Z

For example, a sodium atom (Na) has Z=11 and A=23, so it contains 23−11 = 12 neutrons. An oxygen atom (O) often has Z=8, A=16, giving 8 neutrons.

例如，钠原子（Na）的 Z=11，A=23，因此含有 23−11=12 个中子。氧原子（O）通常 Z=8，A=16，有 8 个中子。

Electrons are arranged in shells: the first shell can hold up to 2 electrons, the second up to 8, and the third up to 8 (at KS3 level). This arrangement determines how elements react.

电子分层排布：第一层最多容纳 2 个电子，第二层最多 8 个，第三层最多 8 个（KS3 阶段）。这种排布决定了元素的化学性质。

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3. Reading the Periodic Table | 阅读周期表

Each element is represented by a symbol, and the periodic table displays its atomic number and relative atomic mass (which is often close to the mass number). The table is arranged in order of increasing atomic number.

每种元素用一个符号表示，周期表上标注了元素的原子序数和相对原子质量（通常接近质量数）。周期表按原子序数递增的顺序排列。

Groups are vertical columns; elements in the same group have the same number of electrons in their outer shell and similar chemical properties. Periods are horizontal rows; the period number tells you how many electron shells are occupied.

族是纵列，同族元素的最外层电子数相同，化学性质相似。周期是横行，周期数代表电子占据的层数。

For quick reference: Group 1 alkali metals (e.g. Na, K) are very reactive with one outer electron; Group 7 halogens (e.g. Cl, Br) have seven outer electrons; Group 0 (noble gases) have full outer shells and are unreactive.

速查：第 1 族碱金属（如 Na、K）最外层 1 个电子，非常活泼；第 7 族卤素（如 Cl、Br）最外层 7 个电子；第 0 族（稀有气体）具有满壳层，不活泼。

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4. Chemical Formulae and Valency | 化学式与化合价

A chemical formula shows the types and numbers of atoms in a substance. For ionic compounds, the formula is determined by the charges on the ions: the total positive charge must balance the total negative charge.

化学式表示物质中原子的种类和数目。对于离子化合物，化学式由离子电荷决定：正负总电荷必须平衡。

Common ions to remember:

需记住的常见离子：

Positive ions / 阳离子	Negative ions / 阴离子
Na⁺, K⁺, Ag⁺	Cl⁻, Br⁻, I⁻
Mg²⁺, Ca²⁺, Cu²⁺, Fe²⁺, Zn²⁺	O²⁻, S²⁻
Al³⁺, Fe³⁺	NO₃⁻, OH⁻, HCO₃⁻
NH₄⁺	SO₄²⁻, CO₃²⁻

To write an ionic formula, swap the numerical charges and write them as subscripts. For example, magnesium chloride: Mg²⁺ and Cl⁻ give MgCl₂. Aluminium oxide: Al³⁺ and O²⁻ give Al₂O₃.

写离子化学式时，将电荷数的绝对值交叉作为下标。例如，氯化镁：Mg²⁺ 和 Cl⁻ 得到 MgCl₂。氧化铝：Al³⁺ 和 O²⁻ 得到 Al₂O₃。

For covalent molecules, the formula simply tells you how many atoms are bonded, e.g. H₂O, CO₂, CH₄, NH₃.

对于共价分子，化学式直接给出键合的原子个数，如 H₂O、CO₂、CH₄、NH₃。

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5. Balancing Equations and Conservation of Mass | 方程配平与质量守恒

The law of conservation of mass states that atoms 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 each type of atom must be the same on both sides of the equation.

质量守恒定律指出，化学反应中原子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，且方程两边每种原子的数目必须相等。

To balance an equation, first write the correct formulae for all reactants and products. Then count the atoms of each element on both sides. Adjust coefficients (the big numbers in front) but never change the subscripts inside a formula.

配平方程时，先写出所有反应物和生成物的正确化学式。然后数两边的每种原子个数。调整化学式前的系数（大数字），但绝不能改变化学式内部的下标。

Example: Hydrogen + oxygen → water.

示例：氢气 + 氧气 → 水。

H₂ + O₂ → 2H₂O

H₂ + O₂ → 2H₂O

Now there are 2 oxygen atoms on each side, but hydrogen is unbalanced. Final balanced equation:

此时两边各有 2 个氧原子，但氢原子数不平衡。最终配平方程式：

2H₂ + O₂ → 2H₂O

2H₂ + O₂ → 2H₂O

This shows that 2 molecules of hydrogen react with 1 molecule of oxygen to produce 2 molecules of water.

这表示 2 个氢分子与 1 个氧分子反应生成 2 个水分子。

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6. Acids, Alkalis and pH | 酸、碱与 pH

An acid is a substance that produces hydrogen ions (H⁺) in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO

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