📚 Year 9 CAIE Chemistry: Quick Reference Guide to Formulas and Theorems | Year 9 CAIE 化学：公式定理速查手册
This handbook gathers every essential formula, definition and theorem you will meet in the Year 9 CAIE Chemistry course. It is designed for fast revision and quick checks before class tests or the end-of-year exam.
本手册汇集了 Year 9 CAIE 化学课程中你会遇到的每一个关键公式、定义和定理。它专为快速复习和课堂测验或年终考试前的速查而设计。
1. Atomic Structure and Notation | 原子结构与符号
The atomic number (Z) tells you how many protons are in the nucleus of an atom. In a neutral atom, the number of electrons equals Z.
原子序数（Z）告诉你原子核内有多少个质子。在中性原子中，电子数等于 Z。
The mass number (A) is the total number of protons plus neutrons in the nucleus.
质量数（A）是原子核内质子与中子的总数。
A = Z + N
where N is the number of neutrons. You can always find the neutron count by subtracting Z from A.
其中 N 是中子数。你始终可以通过 A 减去 Z 得到中子数。
Electrons are arranged in shells around the nucleus. The first shell holds up to 2 electrons, the second up to 8, and the third up to 8 (for the elements you will study).
电子分层排布在原子核周围。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（针对你将学习的元素）。
2. Relative Atomic Mass and Relative Molecular Mass | 相对原子质量与相对分子质量
Relative atomic mass (Aᵣ) is the average mass of an atom of an element compared to 1/12 of the mass of a carbon-12 atom. It has no unit.
相对原子质量（Aᵣ）是一个元素原子的平均质量与一个碳‑12 原子质量的 1/12 相比的比值，无单位。
Relative molecular mass (Mᵣ) is the sum of the relative atomic masses of all the atoms in a molecule.
相对分子质量（Mᵣ）是一个分子中所有原子的相对原子质量之和。
Mᵣ = Σ (Aᵣ × number of atoms of that element)
Example: Mᵣ of H₂O = 2×1 + 16 = 18.
示例：H₂O 的 Mᵣ = 2×1 + 16 = 18。
3. The Mole Concept | 摩尔概念
One mole of any substance contains 6.02 × 10²³ particles. This number is called the Avogadro constant (L or Nₐ).
一摩尔任何物质含有 6.02 × 10²³ 个粒子。这个数字称为阿伏伽德罗常数（L 或 Nₐ）。
The amount of substance (n) links mass and molar mass:
物质的量（n）将质量与摩尔质量联系起来：
n = m / M
where n is in mol, m is mass in grams, and M is molar mass in g/mol. Molar mass has the same numerical value as Mᵣ but with the unit g/mol.
其中 n 的单位是 mol，m 是质量（g），M 是摩尔质量（g/mol）。摩尔质量的数值与 Mᵣ 相同，但有单位 g/mol。
To find the number of particles: N = n × 6.02 × 10²³.
计算粒子数：N = n × 6.02 × 10²³。
4. Empirical and Molecular Formulae | 经验式与分子式
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.
经验式给出化合物中原子的最简整数比。分子式则表示一个分子中每种原子的实际数目。
To find the empirical formula from mass data: convert masses to moles, divide by the smallest number of moles, and write the ratio as whole numbers.
由质量数据求经验式：将质量换算为物质的量，除以最小的物质的量，将比值写成整数。
The molecular formula is a whole‑number multiple of the empirical formula: (empirical formula)₅ where n = Mᵣ of the compound ÷ Mᵣ of the empirical formula.
分子式是经验式的整数倍：(经验式)₅，其中 n = 化合物的 Mᵣ ÷ 经验式的 Mᵣ。
5. Balancing Chemical Equations | 配平化学方程式
Chemical equations use symbols and formulas to describe reactions. The law of conservation of mass requires the same number of each type of atom on both sides.
化学方程式用符号和化学式描述反应。质量守恒定律要求两边每种原子的数目相等。
Balancing is done by placing coefficients in front of formulas, never by changing subscripts inside a formula.
配平是通过在化学式前放置系数，绝不能更改化学式内部的下标。
2H₂ + O₂ → 2H₂O
State symbols show the physical state: (s) solid, (l) liquid, (g) gas, (aq) aqueous solution.
状态符号表示物理状态：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液。
6. States of Matter and Phase Changes | 物质状态与相变
Melting, boiling, freezing and condensation are physical changes. During a change of state, the temperature stays constant while energy is absorbed or released as latent heat.
熔化、沸腾、凝固和冷凝是物理变化。在状态变化过程中，温度保持不变，能量以潜热的形式被吸收或释放。
Sublimation is the change directly from solid to gas (e.g., dry ice). Deposition is the reverse.
升华是从固体直接变为气体（如干冰）。凝华则是相反的过程。
The particle model explains these changes: particles gain energy, move faster and overcome forces of attraction.
粒子模型解释这些变化：粒子获得能量，运动加快并克服吸引力。
7. Solutions and Concentration | 溶液与浓度
Concentration measures how much solute is dissolved in a given volume of solution. It can be expressed as mass concentration (g/dm³) or molar concentration (mol/dm³).
浓度衡量给定体积溶液中溶解了多少溶质。它可以表示为质量浓度（g/dm³）或摩尔浓度（mol/dm³）。
Mass concentration = mass of solute (g) / volume of solution (dm³)
Molar concentration (c) is the amount of solute per unit volume:
摩尔浓度（c）是单位体积溶液中溶质的物质的量：
c = n / V
where c in mol/dm³, n in mol, V in dm³. Note: 1 dm³ = 1000 cm³ = 1 L.
其中 c 的单位为 mol/dm³，n 为 mol，V 为 dm³。注意：1 dm³ = 1000 cm³ = 1 L。
When diluting a solution, the amount of solute stays the same: c₁V₁ = c₂V₂.
稀释溶液时，溶质的物质的量不变：c₁V₁ = c₂V₂。
8. Acids, Bases and pH | 酸、碱与 pH
An acid is a substance that releases H⁺ ions in water. A base neutralises an acid to form a salt and water. An alkali is a soluble base that releases OH⁻ ions.
酸是在水中释放 H⁺ 离子的物质。碱能中和酸生成盐和水。可溶性碱称为碱（alkali），它在水中释放 OH⁻ 离子。
The pH scale (0–14) measures acidity: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline.
pH 标度（0–14）衡量酸碱性：pH < 7 为酸性，pH = 7 为中性，pH > 7 为碱性。
Neutralisation ionic equation (for strong acids and alkalis):
中和的离子方程式（强酸与强碱）：
H⁺ + OH⁻ → H₂O
9. Rates of Reaction | 反应速率
The rate of a reaction tells us how quickly reactants are used up or products are formed. It can be measured by the change in mass, volume of gas, or colour per unit time.
反应速率表示反应物消耗或生成物形成的快慢。它可以通过单位时间内质量、气体体积或颜色的变化来测量。
Average rate = change in quantity / time taken
For a reaction that produces a gas, the rate can be found from the slope of a volume–time graph.
对于产生气体的反应，速率可由体积–时间图的斜率求得。
Factors affecting rate: temperature, concentration (for solutions), pressure (for gases), surface area of solids, and the presence of a catalyst. Increasing temperature or concentration increases the frequency of effective collisions.
影响速率的因素：温度、浓度（对溶液）、压强（对气体）、固体的表面积以及催化剂的存在。升高温度或增大浓度可增加有效碰撞的频率。
10. Chemical Bonding and Properties | 化学键与性质
Ionic bonding occurs when atoms transfer electrons to form oppositely charged ions. The strong electrostatic attraction between cations and anions holds the giant ionic lattice together.
离子键是因原子转移电子形成带相反电荷的离子而产生的。阳离子与阴离子之间强烈的静电引力将巨型离子晶格结合在一起。
Covalent bonding involves the sharing of electron pairs between atoms, forming molecules or giant covalent structures.
共价键涉及原子间共用电子对，形成分子或巨型共价结构。
Metallic bonding consists of positive metal ions surrounded by a sea of delocalised electrons. This explains why metals conduct electricity and are malleable.
金属键由带正电的金属离子沉浸在离域电子的海洋中构成，这解释了金属为何能导电且具有延展性。
| Property | Ionic | Covalent (molecular) | Metallic |
|---|---|---|---|
| Melting/boiling point | High | Low | Usually high |
| Conducts electricity | When molten or dissolved | No | Yes (as solid and liquid) |
| Solubility in water | Often soluble | Varies | Insoluble |
11. Energy Changes in Reactions | 反应中的能量变化
In an exothermic reaction, energy is released to the surroundings, usually as heat. The temperature rises and ΔH is negative.
在放热反应中，能量被释放到周围环境中，通常以热的形式，温度升高且 ΔH 为负值。
In an endothermic reaction, energy is absorbed from the surroundings, the temperature drops and ΔH is positive.
在吸热反应中，能量从环境吸收，温度下降且 ΔH 为正值。
Bond breaking requires energy (endothermic). Bond making releases energy (exothermic). The overall energy change depends on the balance between these two processes.
断键需要能量（吸热），成键释放能量（放热）。总能量变化取决于这两个过程的平衡。
12. Electrolysis Basics | 电解基础
Electrolysis splits an ionic compound into its elements using direct current. Positive ions (cations) move to the negative cathode and gain electrons (reduction). Negative ions (anions) move to the positive anode and lose electrons (oxidation).
电解利用直流电将离子化合物分解为元素。阳离子移向负极（阴极）得电子（还原）；阴离子移向正极（阳极）失电子（氧化）。
For molten lead(II) bromide: at the cathode, Pb²⁺ + 2e⁻ → Pb; at the anode, 2Br⁻ → Br₂ + 2e⁻.
对于熔融溴化铅：阴极，Pb²⁺ + 2e⁻ → Pb；阳极，2Br⁻ → Br₂ + 2e⁻。
In aqueous solutions, the products depend on the reactivity of the ions and the concentration of the solution. At the cathode, hydrogen is produced if the metal is more reactive than hydrogen.
在水溶液中，产物取决于离子的活泼性和溶液浓度。若金属比氢活泼，阴极会生成氢气。
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