📚 Year 8 CIE Chemistry: Formula and Theorem Quick Reference Handbook | Year 8 CIE 化学：公式定理速查手册
This handbook provides a concise summary of the key formulas, laws and theorems required for the Year 8 CIE Chemistry syllabus. Each section presents a fundamental principle followed by a clear explanation, helping you to revise efficiently and master the essential concepts.
本手册为 Year 8 CIE 化学大纲中的关键公式、定律和定理提供简明总结。每一节先给出基本原理，再用清晰的中文解释，帮助你高效复习、掌握核心概念。
1. Law of Conservation of Mass | 质量守恒定律
In any chemical reaction, the total mass of the reactants always equals the total mass of the products. Atoms are neither created nor destroyed, only rearranged. This means the mass before the reaction is exactly the same as the mass after the reaction, provided no gas escapes or enters the system.
在任何化学反应中，反应物的总质量总是等于生成物的总质量。原子既不能被创造也不能被消灭，只能重新排列。这意味着只要没有气体逸出或进入系统，反应前的质量与反应后的质量完全相等。
2. Atomic Structure and Subatomic Particles | 原子结构与亚原子粒子
All matter is made up of atoms. An atom consists of a tiny, dense nucleus containing positively charged protons and neutral neutrons, surrounded by negatively charged electrons orbiting in shells. The number of protons determines the element (atomic number Z). The total number of protons and neutrons gives the mass number A.
所有物质都由原子组成。原子由一个极小的致密原子核和绕核运动的电子构成，核内包含带正电的质子和电中性的中子。质子数决定了元素的种类（原子序数 Z）。质子数和中子数之和为质量数 A。
| Particle | Relative mass | Relative charge | Location |
|---|---|---|---|
| Proton | 1 | +1 | Nucleus |
| Neutron | 1 | 0 | Nucleus |
| Electron | 1/1836 (negligible) | –1 | Shells around nucleus |
质子相对质量为 1，带一个单位正电荷；中子相对质量也为 1，不带电；电子的质量极小（约为质子的 1/1836），带一个单位负电荷。原子整体呈电中性，因此质子数等于电子数。
3. 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 and cannot be broken down into simpler substances by chemical means. A compound is a substance formed when two or more different elements chemically combine in a fixed ratio. A mixture consists of two or more substances (elements or compounds) that are not chemically combined and can be separated by physical methods.
元素是由单一类型原子组成的纯物质，不能用化学方法分解为更简单的物质。化合物是两种或多种不同元素以固定比例通过化学结合形成的物质。混合物则由两种或多种未发生化学结合的物质（元素或化合物）组成，可通过物理方法分离。
4. Chemical Symbols and Formulae | 化学符号与化学式
Each element is represented by a one- or two-letter symbol (e.g., C for carbon, Na for sodium). A chemical formula shows the types and numbers of atoms in a compound. Subscript numbers indicate how many atoms of each element are present. For example, H₂O means two hydrogen atoms and one oxygen atom. Brackets are used when a group of atoms acts as a unit, such as Ca(OH)₂.
每种元素用一个或两个字母的符号表示（如碳 C，钠 Na）。化学式表示化合物中原子的种类和数量，下标数字指示每种元素的原子个数。例如 H₂O 表示两个氢原子和一个氧原子。当一组原子作为一个整体时使用括号，如 Ca(OH)₂。
The valency (combining power) of common ions helps to write correct formulae. For instance, sodium Na⁺ has a valency of 1, oxide O²⁻ has a valency of 2, so the formula of sodium oxide is Na₂O.
常见离子的化合价（结合能力）有助于书写正确的化学式。例如钠离子 Na⁺ 的化合价为 1，氧离子 O²⁻ 的化合价为 2，所以氧化钠的化学式为 Na₂O。
5. Writing and Balancing Chemical Equations | 书写与配平化学方程式
A chemical equation uses symbols and formulae to describe a reaction. The law of conservation of mass requires that the number of atoms of each element is the same on both sides of the arrow. Balancing is achieved by placing coefficients (whole numbers) in front of the formulae. State symbols (s) solid, (l) liquid, (g) gas and (aq) aqueous solution are often added.
化学方程式用符号和化学式描述化学反应。质量守恒定律要求每种元素的原子数目在箭头两侧相等。通过在化学式前添加系数（整数）来实现配平。通常还要标注状态符号：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液。
Example: 2H₂(g) + O₂(g) → 2H₂O(l)
配平步骤：先写下正确的化学式，再用系数使每种原子的总数相等。永远不要改变化学式中的下标来配平。
6. States of Matter and Particle Theory | 物质状态与粒子理论
The kinetic particle theory explains the behaviour of solids, liquids and gases. In solids, particles are closely packed in a fixed arrangement and vibrate in place. In liquids, particles are close together but can move past each other. In gases, particles are far apart and move randomly at high speed. Changes of state (melting, boiling, condensing, freezing) occur when energy is added or removed, but the temperature remains constant during the change itself.
分子运动论解释了固体、液体和气体的行为。固体中粒子紧密排列在固定位置并原地振动；液体中粒子彼此靠近但能相对滑动；气体中粒子间距很大，作高速无规则运动。物态变化（熔化、沸腾、冷凝、凝固）在吸收或释放能量时发生，但在物态变化过程中温度保持不变。
Solid ⇌ Liquid ⇌ Gas (melting/freezing and boiling/condensing)
7. Acids, Bases and the pH Scale | 酸、碱与 pH 值
d nitric acid (HNO₃). Bases are substances that neutralise acids, producing salt and water. Alkalis are soluble bases that release hydroxide ions (OH⁻) in water. The pH scale (0– dity or alkalinity of a solution: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline.
酸是在水中释放氢离子 (H⁺) 的物质。实验室常见的酸有盐酸 (HCl)、硫酸 (H₂SO₄) 和硝酸 (HNO₃)。碱是能中和酸并生成盐和水的物质。可溶性碱称为碱，能在水中释放氢氧根离子 (OH⁻)。pH 值范围 0–14 衡量溶液的酸碱性：pH < 7 为酸性，pH = 7 为中性，pH > 7 为碱性。
Acid + Base → Salt + Water (neutralisation)
酸 + 碱 → 盐 + 水（中和反应）。例如：HCl + NaOH → NaCl + H₂O。
8. Reactivity Series of Metals | 金属活动性顺序
The reactivity series lists metals in order of their tendency to form positive ions. A more reactive metal can displace a less reactive metal from its compound in solution. The series, from most to least reactive, is typically: Potassium (K), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminium (Al), Zinc (Zn), Iron (Fe), Lead (Pb), Copper (Cu), Silver (Ag), Gold (Au).
金属活动性顺序根据金属形成正离子的难易程度排列。较活泼的金属能把较不活泼的金属从其化合物溶液中置换出来。由活泼到不活泼的常见顺序为：钾 (K)、钠 (Na)、钙 (Ca)、镁 (Mg)、铝 (Al)、锌 (Zn)、铁 (Fe)、铅 (Pb)、铜 (Cu)、银 (Ag)、金 (Au)。
). Zinc is more reactive than copper, so it displaces copper from copper sulfate solution.
置换反应示例：Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)。锌比铜活泼，因此能把铜从硫酸铜溶液中置换出来。
9. Separation Techniques for Mixtures | 混合物的分离技术
Different physical separation methods are used depending on the properties of the components in a mixture. Filtration separates an insoluble solid from a liquid (e.g., sand from water). Crystallisation obtains a soluble solid from a solution by evaporating the solvent. Simple distillation separates a solvent from a solution based on boiling point differences. Fractional distillation separates a mixture of miscible liquids (e.g., ethanol and water). Chromatography separates dissolved substances based on their solubility in a solvent.
根据混合物组分的性质差异，可采用不同的物理分离方法。过滤用于分离不溶性固体和液体（如沙子和水）。结晶法通过蒸发溶剂从溶液中获得可溶性固体。简单蒸馏利用沸点差异从溶液中分离溶剂。分馏用于分离互溶液体混合物（如乙醇和水）。色谱法则根据物质在溶剂中溶解度的不同分离溶解的物质。
10. Energy Changes in Chemical Reactions | 化学反应中的能量变化
Chemical reactions involve energy transfers. Exothermic reactions release energy to the surroundings, causing a temperature rise (e.g., combustion, neutralisation). Endothermic reactions absorb energy from the surroundings, causing a temperature drop (e.g., thermal decomposition, photosynthesis). The overall energy change can be observed by measuring temperature differences before and after a reaction.
化学反应涉及能量转移。放热反应向环境释放能量，导致温度升高（如燃烧、中和反应）。吸热反应从环境吸收能量，导致温度降低（如热分解、光合作用）。通过测量反应前后的温度变化可以观察总能量变化。
gy is conserved: total energy of reactants = total energy of products + energy transferred
能量永远守恒：反应物的总能量 = 生成物的总能量 + 转移的能量。
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