📚 KS3 CCEA Chemistry: Quick Reference Handbook of Formulas and Theorems | KS3 CCEA 化学：公式定理速查手册
This handbook brings together the most essential formulas, definitions and theorems you will meet in KS3 CCEA Chemistry. Use it to check your understanding, support your homework, and build a solid foundation before moving on to GCSE. Each entry is written to match the Northern Ireland Curriculum at Key Stage 3, covering atoms, reactions, acids, materials and more.
本手册汇集了 KS3 CCEA 化学课程中最关键的公式、定义和定理。可用来检查理解、辅助作业，并在进入 GCSE 之前打好坚实基础。每一条内容都与北爱尔兰第三关键阶段的课程相匹配，涵盖原子、反应、酸、材料等主题。
1. Structure of the Atom | 原子结构
Atoms contain a tiny central nucleus made of protons and neutrons, surrounded by electrons arranged in shells. The number of protons (atomic number) determines the element, while the total of protons and neutrons gives the mass number.
原子含有一个由质子和中子构成的微小中心原子核，核外电子分层排布。质子数（原子序数）决定了元素种类，而质子数与中子数之和为质量数。
For a neutral atom, the number of electrons equals the number of protons. Ions form when atoms gain or lose electrons, becoming negatively or positively charged.
对于中性原子，电子数等于质子数。原子得到或失去电子后形成离子，带负电或正电。
number of protons = atomic number; mass number = protons + neutrons
2. Writing Chemical Formulae | 化学式的书写
Chemical formulae use element symbols and small subscript numbers to show how many atoms of each element are present in a substance. The symbol for the metal (or positive part) is written first in a compound.
化学式使用元素符号和小下标数字来表示物质中各元素的原子个数。在化合物中，金属（或带正电部分）的符号写在前面。
When ions combine to form an ionic compound, the total positive charge must balance the total negative charge. For example, sodium chloride: Na+ and Cl- give NaCl. Magnesium chloride: Mg2+ needs two Cl- ions, giving MgCl2.
当离子结合为离子化合物时，总正电荷必须与总负电荷平衡。例如氯化钠：Na+ 与 Cl- 得到 NaCl。氯化镁：Mg2+ 需要两个 Cl-，因此化学式为 MgCl2。
formula mass = sum of relative atomic masses of all atoms in the formula
3. Balancing Chemical Equations | 化学方程式的配平
A chemical equation describes a reaction using symbols and formulae. According to the law of conservation of mass, atoms cannot be created or destroyed, so we must balance the equation so that the same number of each type of atom appears on both sides.
化学方程式用符号和化学式描述化学反应。根据质量守恒定律，原子不能被创造或消灭，因此必须配平方程式，使每一种原子的总数在反应前后相等。
To balance an equation, change only the large numbers (coefficients) in front of the substances; never alter the small subscript numbers inside a formula. For example: H2 + O2 → H2O becomes 2H2 + O2 → 2H2O.
配平方程式时，只改变物质前面的大数字（系数），绝不能改动化学式中的小下标数字。例如：H2 + O2 → H2O 配平后为 2H2 + O2 → 2H2O。
4. Conservation of Mass | 质量守恒定律
The total mass of the reactants in a chemical reaction is equal to the total mass of the products. This happens because atoms are simply rearranged, not lost or gained.
化学反应中反应物的总质量等于生成物的总质量。这是因为原子只是重新排列，没有损失也没有增加。
In a reaction that appears to show a mass change – for example, when a gas is released – the mass of the gas must be included in the total mass of the products. An experiment using a closed container can demonstrate that mass is conserved.
在看似质量发生变化的反应中（例如有气体释放时），必须将气体的质量计入生成物的总质量中。使用密闭容器的实验可以证明质量守恒。
5. Relative Atomic Mass and Relative Formula Mass | 相对原子质量与相对式量
The relative atomic mass (Ar) of an element compares the average mass of its atoms to 1/12 of the mass of a carbon‑12 atom. It has no units. The relative atomic mass is roughly equal to the mass number for most elements.
元素的相对原子质量（Ar）是该元素原子平均质量与一个碳‑12 原子质量的 1/12 之比，没有单位。对于大多数元素，相对原子质量约等于其质量数。
The relative formula mass (Mr) of a compound is found by adding up the relative atomic masses of all the atoms in its formula. For example, Mr of H2O = (2×1) + 16 = 18.
化合物的相对式量（Mr）是将化学式中所有原子的相对原子质量相加得到的。例如 H2O 的 Mr = (2×1) + 16 = 18。
6. Empirical and Molecular Formulae | 实验式与分子式
The empirical formula gives the simplest whole‑number ratio of atoms in a compound. The molecular formula shows the actual number of atoms of each element in a molecule.
实验式表示化合物中原子个数的最简整数比。分子式表示一个分子中各元素原子的实际数目。
For many simple substances at KS3, the empirical and molecular formulae are the same. For example, water (H2O) and carbon dioxide (CO2) already show the simplest ratio. Glucose (C6H12O6) has the empirical formula CH2O.
在 KS3 阶段的许多简单物质中，实验式和分子式是相同的。例如水（H2O）和二氧化碳（CO2）已经显示了最简比。葡萄糖（C6H12O6）的实验式为 CH2O。
7. Acids, Bases and the pH Scale | 酸、碱和 pH 标度
An acid is a substance that releases hydrogen ions (H+) in water. A base is a substance that can neutralise an acid, and an alkali is a soluble base that releases hydroxide ions (OH-) in water.
酸是在水中释放氢离子（H+）的物质。碱是可以中和酸的物质，而可溶于水的碱称为碱溶液，它在水中释放氢氧根离子（OH-）。
The pH scale measures how acidic or alkaline a solution is. Values range from 0 (very acidic) to 14 (very alkaline), with 7 being neutral. Universal indicator or a pH probe can be used to measure pH.
pH 标度用来衡量溶液的酸碱度。数值范围从 0（强酸性）到 14（强碱性），7 为中性。可使用通用指示剂或 pH 探头测量 pH 值。
8. Neutralisation and Salt Formation | 中和反应与盐的生成
(or alkali) to form a salt and water. The general equation is: acid + base → salt + water.
中和反应是酸与碱（或碱溶液）反应生成盐和水的反应。通式为：酸 + 碱 → 盐 + 水。
e. The identity of the salt depends on the acid used and the metal in the base or carbonate.
当金属碳酸盐与酸反应时，生成盐、水和二氧化碳气体：酸 + 金属碳酸盐 → 盐 + 水 + 二氧化碳。所生成盐的种类取决于所用的酸和碱或碳酸盐中的金属。
9. Reactivity Series and Displacement | 反应活性顺序与置换反应
The reactivity series lists metals in order of how readily they react. A more reactive metal will displace a less reactive metal from its compound in solution.
反应活性顺序根据金属反应难易程度排列。较活泼的金属能从溶液中把较不活泼的金属从其化合物中置换出来。
For example, zinc is more reactive than copper, so zinc added to copper(II) sulfate solution displaces copper: Zn + CuSO4 → ZnSO4 + Cu. Carbon is also included in the series because it can displace some metals from their oxides.
例如锌比铜活泼，将锌加入硫酸铜溶液中会置换出铜：Zn + CuSO4 → ZnSO4 + Cu。碳也包含在活性顺序中，因为它可以从某些金属氧化物中置换出金属。
10. States of Matter and Particle Theory | 物质状态与粒子理论
Materials can exist as solids, liquids or gases. According to particle theory, all matter is made of tiny moving particles. The arrangement and movement of these particles determine the state.
物质可以以固态、液态或气态存在。根据粒子理论，所有物质都由微小的运动粒子组成。粒子的排列和运动方式决定了物质的状态。
In a solid, particles are closely packed in a regular pattern and vibrate in fixed positions. In a liquid, particles are close but can move past each other. In a gas, particles are far apart and move quickly in all directions.
固态中粒子紧密排列、有规则结构，在固定位置振动。液态中粒子彼此靠近但能互相滑动。气态中粒子间隔很远，向各个方向快速运动。
melting point: solid → liquid; boiling point: liquid → gas
11. Solubility and Saturated Solutions | 溶解度与饱和溶液
Solubility is a measure of how much solute can dissolve in a given amount of solvent at a particular temperature. A saturated solution contains the maximum mass of solute that can dissolve at that temperature; any extra solute will remain undissolved.
溶解度衡量在特定温度下，一定量溶剂中能溶解多少溶质。饱和溶液含有该温度下所能溶解的最大溶质质量；任何额外溶质将不再溶解。
Solubility usually increases with temperature for solids, but for gases it decreases as temperature rises. Graphs called solubility curves show how solubility changes with temperature.
固体溶解度通常随温度升高而增加，但气体的溶解度随温度升高而下降。溶解度曲线图显示了溶解度随温度的变化情况。
12. Tests for Common Gases | 常见气体的检验
There are simple laboratory tests to identify hydrogen, oxygen, carbon dioxide and chlorine. Recognising these tests is an important practical skill.
在实验室中，有简单的检验方法可用于鉴别氢气、氧气、二氧化碳和氯气。识别这些检验方法是重要的实验技能。
- Hydrogen (H2): A lit splint produces a squeaky pop.
氢气（H2）：点燃的木条靠近时有爆鸣声。 - Oxygen (O2): A glowing splint relights.
氧气（O2）：带火星的木条复燃。 - Carbon dioxide (CO2): Turns limewater (calcium hydroxide solution) milky or cloudy.
二氧化碳（CO2）：使石灰水（氢氧化钙溶液）变浑浊。 - Chlorine (Cl2): Bleaches damp litmus paper or universal indicator paper, turning it white.
氯气（Cl2）：使湿润的石蕊试纸或通用指示剂试纸漂白变白。
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