📚 Year 8 CIE Chemistry: Quick-reference Formula and Theorem Handbook | Year 8 CIE 化学：公式定理速查手册
This handbook provides a rapid, topic-based summary of the essential formulas, rules, and theorems needed for the Year 8 CIE Chemistry syllabus. Use it to reinforce concepts, check definitions, and practise problem-solving. Each section pairs key English explanations with matching Chinese explanations for bilingual clarity.
本手册按主题快速梳理 Year 8 CIE 化学课程中必需的公式、规则与定理。可用于巩固概念、核查定义和练习解题。每个知识点都提供对应的中英文双语解释，清晰易懂。
1. Atomic Structure and Notation | 原子结构与符号表示
Every element is represented by a standard nuclear symbol. The mass number (A) is the sum of protons and neutrons, while the atomic number (Z) is the number of protons. In a neutral atom, the number of electrons equals Z. Neutrons = A – Z.
每种元素的原子用标准核素符号表示。质量数 (A) 为质子数与中子数之和，原子序数 (Z) 是质子数。中性原子中，电子数等于 Z。中子数 = A – Z。
Nuclear symbol: &supA;ₐX Example: ¹²ₐC (6 protons, 6 neutrons)
核素符号: &supA;ₐX 例如: ¹²ₐC（6个质子，6个中子）
Isotopes are atoms of the same element with different numbers of neutrons. They have identical Z but different A. Chemical properties of isotopes are essentially the same because they have the same electron arrangement.
同位素是同种元素的原子，其中子数不同。它们有相同的 Z 但不同的 A。由于电子排布相同，同位素的化学性质基本相同。
- Number of protons = Z
质子数 = Z - Number of electrons = Z (in a neutral atom)
电子数 = Z（中性原子中） - Number of neutrons = A – Z
中子数 = A – Z
2. The Periodic Table: Groups and Periods | 元素周期表：族与周期
The periodic table arranges elements in order of increasing atomic number. Horizontal rows are called periods; the period number tells you the number of electron shells an atom has. Vertical columns are called groups; the group number for the main groups gives the number of electrons in the outer shell.
周期表按原子序数递增排列。横行为周期，周期数等于原子的电子层数。纵列为族，主族元素的族数等于最外层电子数。
Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons. For example, Group 1 elements (alkali metals) all have 1 outer electron and react vigorously with water. Group 7 elements (halogens) have 7 outer electrons and form diatomic molecules such as F₂, Cl₂. Group 8 (noble gases) have full outer shells and are unreactive.
同族元素化学性质相似，因为它们的最外层电子数相同。例如，第 1 族碱金属都有 1 个最外层电子，与水剧烈反应。第 7 族卤素最外层有 7 个电子，形成双原子分子，如 F₂、Cl₂。第 8 族稀有气体具有满壳层结构，化学性质不活泼。
Period number = number of occupied electron shells. Group number (for Groups 1–8) = number of outer-shell electrons. Metallic character decreases across a period and increases down a group.
周期数 = 已占用的电子层数。族数（第 1–8 族）= 最外层电子数。同一周期从左到右金属性减弱，同一族从上到下金属性增强。
3. Chemical Formulae and Naming Compounds | 化学式与化合物命名
Ionic compounds are formed between metals and non-metals. The overall charge must be zero. Use the cross-over rule: the charge on one ion becomes the subscript of the other ion. For example, sodium oxide: Na⁺ and O²⁻ → Na₂O.
离子化合物由金属与非金属形成。整体必须呈电中性。使用交叉法书写化学式：一种离子的电荷数成为另一种离子的下标。例如，氧化钠：Na⁺ 和 O²⁻ → Na₂O。
Covalent compounds (non-metal + non-metal) are named using prefixes to show the number of atoms: mono- (1), di- (2), tri- (3), tetra- (4), penta- (5). Carbon dioxide CO₂, sulfur trioxide SO₃. The prefix ‘mono-‘ is often omitted for the first element.
共价化合物（非金属 + 非金属）的命名使用词头表示原子个数：mono- (1)、di- (2)、tri- (3)、tetra- (4)、penta- (5)。二氧化碳 CO₂，三氧化硫 SO₃。第一个元素通常省略词头 “mono-“。
Common polyatomic ions that you must know: sulphate SO₄²⁻, nitrate NO₃⁻, carbonate CO₃²⁻, hydroxide OH⁻, ammonium NH₄⁺, phosphate PO₄³⁻ (sometimes introduced). When writing a formula containing a polyatomic ion, use brackets if more than one unit is needed, e.g. Ca(OH)₂, Al₂(SO₄)₃.
必须掌握的常见多原子离子：硫酸根 SO₄²⁻、硝酸根 NO₃⁻、碳酸根 CO₃²⁻、氢氧根 OH⁻、铵根 NH₄⁺、磷酸根 PO₄³⁻（有时引入）。书写含多原子离子的化学式时，若要表示超过一个离子单元，需用括号，如 Ca(OH)₂、Al₂(SO₄)₃。
| Valency / 化合价 | Example ions / 离子举例 |
|---|---|
| 1 | Na⁺, K⁺, Cl⁻, OH⁻, NH₄⁺ |
| 2 | Mg²⁺, Ca²⁺, O²⁻, SO₄²⁻, CO₃²⁻ |
| 3 | Al³⁺, Fe³⁺, PO₄³⁻ |
4. Writing and Balancing Chemical Equations | 书写与配平化学方程式
The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction. Therefore, a chemical equation must have the same number of each type of atom on both sides. This is achieved by placing coefficients (large numbers) in front of the formulae.
质量守恒定律指出，化学反应中原子的种类和数目保持不变。因此，化学方程式两边的每种原子数目必须相等。这通过在化学式前面添加系数（大数字）实现。
Steps: write the correct formulae for all reactants and products; count the number of each atom on each side; add coefficients to balance atoms, starting with the most complex substance; check all atoms balance; add state symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).
配平步骤：写出所有反应物与生成物的正确化学式；数出两边各元素的原子个数；从最复杂的物质开始添加系数使原子数相等；检查所有原子是否配平；添加状态符号：(s) 固体、(l) 液体、(g) 气体、(aq) 水溶液。
Example: H₂ + O₂ → H₂O. Balanced: 2H₂ + O₂ → 2H₂O.
示例：H₂ + O₂ → H₂O。配平后：2H₂ + O₂ → 2H₂O。
5. States of Matter and Kinetic Particle Theory | 物质状态与粒子动理论
Kinetic particle theory explains the behaviour of solids, liquids and gases in terms of the arrangement and motion of particles (atoms, molecules or ions).
粒子动理论从粒子（原子、分子或离子）的排列与运动角度解释固体、液体和气体的行为。
- Solid: particles closely packed in a regular pattern; vibrate in fixed positions; definite shape and volume.
固体：粒子紧密排列，有规则结构；在固定位置振动；有固定形状和体积。 - Liquid: particles close together but disordered; can move past each other; fixed volume but takes the shape of the container.
液体：粒子间距小但排列无序；可以相互滑动；有固定体积但形状随容器而变。 - Gas: particles far apart, moving randomly at high speeds; no fixed shape or volume; can be compressed.
气体：粒子间距大，快速随机运动；没有固定形状和体积；可以被压缩。
Changes of state are physical changes: melting (solid → liquid), freezing (liquid → solid), boiling/evaporation (liquid → gas), condensation (gas → liquid), sublimation (solid → gas). During a change of state, the temperature remains constant until the change is complete, as energy is used to break forces between particles rather than to raise temperature.
状态变化是物理变化：熔化（固 → 液）、凝固（液 → 固）、沸腾/蒸发（液 → 气）、冷凝（气 → 液）、升华（固 → 气）。在状态变化过程中，温度保持不变直到完成，因为此时能量用于克服粒子间的引力，而不是使温度升高。
Diffusion is the spontaneous mixing of particles due to their random motion and is faster in gases than in liquids, and faster at higher temperatures because particles have more kinetic energy.
扩散是由于粒子随机运动而发生的自发混合，气体中扩散比液体中快，温度升高扩散加快，因为粒子动能增加。
6. Ionic and Covalent Bonding | 离子键与共价键
Ionic bonding occurs between metals and non-metals. Metal atoms lose electrons to form positive cations; non-metal atoms gain electrons to form negative anions. The electrostatic attraction between oppositely charged ions forms a giant ionic lattice. The formula of an ionic compound shows the simplest ratio of ions, e.g. NaCl, MgO.
离子键存在于金属与非金属之间。金属原子失去电子形成阳离子；非金属原子得到电子形成阴离子。正负离子间的静电引力构成巨型离子晶格。离子化合物的化学式表示离子的最简整数比，如 NaCl、MgO。
Covalent bonding occurs between non-metal atoms. Atoms share pairs of electrons to achieve a full outer shell, forming molecules (or giant covalent structures). Simple molecular substances have low melting and boiling points because the intermolecular forces are weak. Giant covalent structures like diamond and silicon dioxide have very high melting points because all atoms are linked by strong covalent bonds in a network.
共价键存在于非金属原子之间。原子共用电子对以达到满壳层结构，形成分子（或巨型共价结构）。简单分子物质的熔点和沸点较低，因为分子间作用力弱。像金刚石和二氧化硅这样的巨型共价结构具有非常高的熔点，因为所有原子通过强共价键连接成网络。
The ‘octet rule’ tendency: atoms tend to gain, lose or share electrons to acquire the stable electron arrangement of a noble gas (usually 8 electrons in the outer shell, except hydrogen which aims for 2). This rule explains ion charges and the number of covalent bonds an atom typically forms.
八隅体规则趋向：原子倾向于通过得失或共用电子以达到稀有气体的稳定电子构型（最外层通常为 8 个电子，氢则为 2 个）。此规则可解释离子所带电荷和原子通常形成的共价键数目。
7. Relative Atomic Mass and Relative Molecular Mass | 相对原子质量与相对分子质量
The relative atomic mass (Aᵣ) of an element is the average mass of its atoms compared to 1/12 of the mass of a carbon-12 atom. It has no units. Aᵣ values are given in the periodic table.
元素的相对原子质量 (Aᵣ) 是其原子的平均质量与一个碳-12 原子质量的 1/12 的比值，没有单位。Aᵣ 值可在周期表中查得。
Aᵣ = (average mass of one atom of the element) ÷ (1/12 × mass of one ¹²C atom)
Aᵣ =（该元素一个原子的平均质量）÷（1/12 × 一个 ¹²C 原子的质量）
The relative molecular mass (Mᵣ) of a molecule is the sum of the Aᵣ values of all the atoms in the formula. For ionic compounds, the term relative formula mass is used, but the calculation is exactly the same. Mᵣ also has no units.
分子的相对分子质量 (Mᵣ) 等于化学式中所有原子的 Aᵣ 之和。对于离子化合物，使用相对式量一词，但计算方法完全相同。Mᵣ 也没有单位。
Example: Mᵣ of H₂O = (2 × 1) + 16 = 18. Mᵣ of CaCO₃ = 40 + 12 + (3 × 16) = 100.
示例：H₂O 的 Mᵣ = (2 × 1) + 16 = 18。CaCO₃ 的 Mᵣ = 40 + 12 + (3 × 16) = 100。
The percentage by mass of an element in a compound = (total mass of that element in the formula ÷ Mᵣ) × 100%.
化合物中某元素的质量分数 =（化学式中该元素的总质量 ÷ Mᵣ）× 100%。
% Element = (n × Aᵣ of element / Mᵣ) × 100%
8. Acids, Bases and Neutralisation | 酸、碱与中和反应
An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. Acids have a pH less than 7 and turn litmus red. Common strong acids: hydrochloric acid HCl(aq), sulfuric acid H₂SO₄(aq), nitric acid HNO₃(aq).
酸是溶于水时产生氢离子 (H⁺) 的物质。酸的 pH 小于 7，使石蕊变红。常见强酸：盐酸 HCl(aq)、硫酸 H₂SO₄(aq)、硝酸 HNO₃(aq)。
A base is a substance that can neutralise an acid. An alkali is a soluble base that releases hydroxide ions (OH⁻) in water. Alkalis have a pH greater than 7 and turn litmus blue.
碱是可以中和酸的物质。可溶性碱称做碱液，在水中释放氢氧根离子 (OH⁻)。碱液的 pH 大于 7，使石蕊变蓝。
Neutralisation: acid + base → salt + water. The ionic equation for neutralisation is H⁺ + OH⁻ → H₂O.
中和反应：酸 + 碱 → 盐 + 水。中和反应的离子方程式为 H⁺ + OH⁻ → H₂O。
The name of a salt is derived from the metal (or ammonium) and the acid. Hydrochloric acid produces chlorides; sulfuric acid produces sulfates; nitric acid produces nitrates.
盐的名称由金属（或铵根）和酸根决定。盐酸生成氯化物；硫酸生成硫酸盐；硝酸生成硝酸盐。
Indicators such as litmus, phenolphthalein and universal indicator show different colours at different pH values. Universal indicator gives a full pH colour range: red (strongly acidic) ↔ green (neutral) ↔ purple (strongly alkaline).
指示剂如石蕊、酚酞和通用指示剂在不同 pH 下显示不同颜色。通用指示剂可显示完整的 pH 颜色范围：红（强酸）↔ 绿（中性）↔ 紫（强碱）。
9. Reactions of Acids with Metals and Carbonates | 酸与金属和碳酸盐的反应
Acids react with reactive metals (above hydrogen in the reactivity series) to produce a salt and hydrogen gas.
酸与活泼金属（在金属活动性顺序中排在氢之前）反应生成盐和氢气。
Metal + Acid → Salt + Hydrogen
金属 + 酸 → 盐 + 氢气
Example: Zn + 2HCl → ZnCl₂ + H₂. The test for hydrogen gas is a lit splint producing a squeaky pop.
示例：Zn + 2HCl → ZnCl₂ + H₂。验证氢气的方法是用点燃的木条靠近，产生清脆的爆鸣声（扑哧声）。
Acids react with metal carbonates to produce a salt, water and carbon dioxide gas.
酸与金属碳酸盐反应生成盐、水和二氧化碳气体。
Carbonate + Acid → Salt + Water + Carbon dioxide
碳酸盐 + 酸 → 盐 + 水 + 二氧化碳
Example: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Carbon dioxide turns limewater (calcium hydroxide solution) milky or cloudy.
示例：CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂。二氧化碳可使石灰水（氢氧化钙溶液）变浑浊。
10. Rate of Reaction and Collision Theory | 反应速率与碰撞理论
The rate of a chemical reaction is how quickly reactants are consumed or products are formed. It can be increased by raising temperature, increasing concentration (for solutions), increasing pressure (for gases), using smaller solid particles (increased surface area) or adding a catalyst.
化学反应速率是指反应物消耗或生成物形成的快慢。可通过升高温度、提高浓度（溶液）、增加压强（气体）、使用更小颗粒的固体（增大表面积）或加入催化剂来提高反应速率。
Collision theory: particles must collide with sufficient energy (activation energy) and with the correct orientation for a reaction to occur. Increasing temperature increases both the frequency of collisions and the proportion of particles with energy equal to or greater than the activation energy. Increasing concentration, pressure, or surface area increases the frequency of collisions.
碰撞理论：粒子必须碰撞且具有足够的能量（活化能）和正确的取向才能发生反应。升高温度既增加碰撞频率，也增加能量达到或超过活化能的粒子比例。增大浓度、压强或表面积会增加碰撞频率。
A catalyst speeds up a reaction without being used up. It provides an alternative reaction pathway with a lower activation energy, so more particles have sufficient energy to react when they collide.
催化剂能加快反应速率而自身不被消耗。它提供一条活化能较低的替代反应路径，因此更多粒子在碰撞时具有足够的能量发生反应。
11. Types of Chemical Reactions | 化学反应类型
It is useful to classify reactions into several general types to predict products and write equations.
将化学反应分类有助于预测生成物和书写方程式。
- Combination (synthesis): two or more substances combine to form one product. A + B → AB.
化合反应：两种或多种物质结合生成一种产物。A + B → AB。例如 2Mg + O₂ → 2MgO。 - Decomposition: a compound breaks down into simpler substances. AB → A + B. Thermal decomposition often requires heating.
分解反应：一种化合物分解成更简单的物质。AB → A + B。热分解常需加热。例如 CaCO₃ → CaO + CO₂。 - Displacement: a more reactive element takes the place of a less reactive element in a compound. A + BC → AC + B.
置换反应：较活泼的元素从化合物中置换出较不活泼的元素。A + BC → AC + B。例如 Fe + CuSO₄ → FeSO₄ + Cu。 - Combustion: a substance reacts rapidly with oxygen, releasing heat and light. Complete combustion of hydrocarbons produces CO₂ and H₂O. Example: CH₄ + 2O₂ → CO₂ + 2H₂O.
燃烧反应：物质与氧气快速反应，放出热和光。碳氢化合物完全燃烧生成 CO₂ 和 H₂O。示例：CH₄ + 2O₂ → CO₂ + 2H₂O。 - Neutralisation: already covered, acid + base → salt + water.
中和反应：已述，酸 + 碱 → 盐 + 水。 - Precipitation: two solutions react to form an insoluble solid (precipitate). e.g. AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq).
沉淀反应：两种溶液反应生成不溶性固体（沉淀）。例如 AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)。
12. Electrolysis (Basic Concepts) | 电解（基础概念）
Electrolysis is the decomposition of an ionic compound using direct current electricity. The ionic compound must be molten or dissolved in water so that the ions are free to move. The two electrodes, made of a conducting material (often graphite or platinum), are connected to a power supply. The positive electrode is called the anode; the negative electrode is the cathode.
电解是利用直流电分解离子化合物的过程。离子化合物必须处于熔融态或溶于水，使离子能够自由移动。两个电极由导电材料（常用石墨或铂）制成，与电源相连。正极称为阳极，负极称为阴极。
During electrolysis, positive cations move to the cathode to gain electrons (reduction); negative anions move to the anode to lose electrons (oxidation).
电解过程中，阳离子移向阴极，获得电子（还原）；阴离子移向阳极，失去电子（氧化）。
Example: electrolysis of molten sodium chloride. Anode: 2Cl⁻ → Cl₂ + 2e⁻ (oxidation). Cathode: Na⁺ + e⁻ → Na (reduction). Overall: 2NaCl(l) → 2Na(l) + Cl₂(g).
示例：熔融氯化钠的电解。阳极：2Cl⁻ → Cl₂ + 2e⁻（氧化）。阴极：Na⁺ + e⁻ → Na（还原）。总反应：2NaCl(l) → 2Na(l) + Cl₂(g)。
In aqueous electrolysis, water may be involved. For example, in dilute sodium chloride solution, hydroxide ions OH⁻ are discharged at the anode in preference to Cl⁻ (depending on concentration and electrode material), giving O₂ rather than Cl₂. At Year 8 level, the focus is usually on the molten example and the general principle.
在水溶液电解中，水可能参与反应。例如，在稀氯化钠溶液中，氢氧根离子 OH⁻ 优先于 Cl⁻ 在阳极放电（取决于浓度与电极材料），从而生成 O₂ 而非 Cl₂。Year 8 阶段通常重点掌握熔融态的例子和基本原理。
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