📚 Year 9 WJEC Chemistry: Formula & Theorem Quick-Reference Handbook | WJEC 九年级化学公式定理速查手册
This handbook gathers the essential formulas, laws, and principles you will encounter in Year 9 WJEC Chemistry. Use it as a quick revision aid to reinforce your understanding of atomic structure, chemical reactions, and the behaviour of substances.
本手册汇总了 WJEC 九年级化学中必考的重要公式、定律与原理。你可以把它当作快速复习工具，帮助巩固对原子结构、化学反应以及物质行为的理解。
1. Law of Conservation of Mass | 质量守恒定律
The total mass of reactants before a chemical reaction is always equal to the total mass of products after the reaction. No atoms are created or destroyed; they are simply rearranged.
化学反应前所有反应物的总质量，总是等于反应后所有生成物的总质量。原子既不会凭空产生，也不会凭空消失，它们只是重新排列了。
Total mass of reactants = Total mass of products
反应物总质量 = 生成物总质量
This principle was established by Antoine Lavoisier and is the foundation for balancing chemical equations.
这条原理由拉瓦锡确立，是配平化学方程式的基础。
2. Relative Atomic Mass & Atomic Structure | 相对原子质量与原子结构
Atoms consist of protons, neutrons, and electrons. The relative atomic mass (Aᵣ) of an element is the average mass of its atoms compared to 1/12 the mass of a carbon‑12 atom.
原子由质子、中子和电子构成。元素的相对原子质量（Aᵣ）是其原子的平均质量与碳‑12 原子质量的 1/12 相比较而得到的数值。
Relative atomic mass (Aᵣ) ≈ number of protons + number of neutrons
相对原子质量 (Aᵣ) ≈ 质子数 + 中子数
| Particle | Relative charge | Relative mass |
|---|---|---|
| Proton 质子 | +1 | 1 |
| Neutron 中子 | 0 | 1 |
| Electron 电子 | -1 | 1/1836 (negligible 可忽略) |
In a neutral atom, the number of protons equals the number of electrons.
在中性原子中，质子数等于电子数。
3. Chemical Formulae & Valency | 化学式与化合价
A chemical formula shows the types and numbers of atoms in a substance. Valency (combining power) tells us how many bonds an atom can form.
化学式表示物质中原子的种类和数目。化合价（结合能力）告诉我们一个原子能形成多少个化学键。
To write the formula of an ionic compound, use the ‘cross‑over’ method: swap the valencies of the two ions and write them as subscripts. Simplify if possible.
书写离子化合物的化学式时，使用“交叉”法：将两种离子的化合价互换并写成下标，必要时化简。
Valency of Aₓ⁺ and Bᵧ⁻ → formula AᵧBₓ
A⁺ B⁻ → 化学式 A₁B₁，直接写作 AB
Common valencies: Group 1 elements = +1, Group 2 = +2, Group 17 (halogens) = –1, Group 16 (oxygen) = – ve variable valencies but Year 9 usually focuses on simple examples like Cu²⁺, Fe²⁺, Fe³⁺.
常见化合价：第 1 族 = +1，第 2 族 = +2，第 17 族（卤素）= –1，第 16 族（氧）= –2。过渡金属常有多种化合价，但九年级主要接触 Cu²⁺、Fe²⁺、Fe³⁺ 等简单例子。
4. Writing Balanced Equations | 书写配平方程式
A balanced symbol equation follows the Law of Conservation of Mass. You must have the same number of each type of atom on both sides of the arrow.
配平的化学符号方程式遵循质量守恒定律。箭头两边每一种原子的总数必须相同。
atoms → add coefficients (big numbers) to balance → add state symbols (s), (l), (g), (aq).
步骤：写文字方程式 → 替换为化学符号 → 数原子数 → 添加化学计量数（配平大系数）→ 标注状态符号 (s), (l), (g), (aq)。
State symbols: (s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous (dissolved in water).
状态符号：(s) 固体，(l) 液体，(g) 气体，(aq) 水溶液。
Example: hydrogen + oxygen → water. 2H₂(g) + O₂(g) → 2H₂O(l).
示例：氢气 + 氧气 → 水。 2H₂(g) + O₂(g) → 2H₂O(l)。
5. States of Matter & Changes | 物质状态与变化
Matter exists in three main states: solid, liquid, and gas. Changes of state are physical changes and no new substances are formed.
物质主要以三种状态存在：固态、液态和气态。状态变化属于物理变化，没有新物质生成。
| Change | Name | Energy change |
|---|---|---|
| Solid → Liquid | Melting 熔化 | Energy absorbed 吸热 |
| Liquid → Gas | Boiling/Evaporation 沸腾/蒸发 | Energy absorbed 吸热 |
| Gas → Liquid | Condensing 冷凝 | Energy released 放热 |
| Liquid → Solid | Freezing 凝固 | Energy released 放热 |
| Solid → Gas | Sublimation 升华 | Energy absorbed 吸热 |
The energy of the particles increases during melting and boiling; it decreases during freezing and condensing.
粒子的能量在熔化和沸腾过程中增加，在凝固和冷凝过程中减少。
6. Acids, Bases & pH | 酸、碱与pH
Acids release H⁺ ions in water; bases release OH⁻ ions in water. Alkalis are soluble bases. pH is a measure of the concentration of H⁺ ions.
酸在水中释放 H⁺ 离子；碱在水中释放 OH⁻ 离子。可溶性碱称为碱溶液。pH 是衡量 H⁺ 离子浓度的标度。
pH scale: 0 → acidic, 7 → neutral, 14 → alkaline
pH 标度：0 → 酸性，7 → 中性，14 → 碱性
Universal indicator and pH probes are used to measure pH. Acids turn blue litmus red; alkalis turn red litmus blue.
通用指示剂和 pH 探头用于测定 pH。酸使蓝色石蕊试纸变红，碱使红色石蕊试纸变蓝。
Common laboratory acids: hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃). Common alkalis: sodium hydroxide (NaOH), potassium hydroxide (KOH).
实验室常用酸：盐酸 HCl、硫酸 H₂SO₄、硝酸 HNO₃。常用碱：氢氧化钠 NaOH、氢氧化钾 KOH。
7. Neutralisation | 中和反应
Neutralisation is the reaction between an acid and a base to form a salt and water. The H⁺ ions from the acid combine with OH⁻ ions from the base to produce water molecules.
中和反应是酸与碱反应生成盐和水的过程。酸中的 H⁺ 离子与碱中的 OH⁻ 离子结合生成水分子。
Acid + Base → Salt + Water
酸 + 碱 → 盐 + 水
Ionic equation for neutralisation: H⁺(aq) + OH⁻(aq) → H₂O(l).
中和反应的离子方程式：H⁺(aq) + OH⁻(aq) → H₂O(l)。
: hydrochloric acid + sodium hydroxide → sodium chloride + water. HCl + NaOH → NaCl + H₂O.
示例：盐酸 + 氢氧化钠 → 氯化钠 + 水。 HCl + NaOH → NaCl + H₂O。
8. Reactivity Series | 活动性顺序
The reactivity series lists metals in order of their reactivity. A more reactive metal can displace a less reactive metal from its compound.
活动性顺序是按金属活泼程度排列的列表。较活泼的金属能将较不活泼的金属从其化合物中置换出来。
Potassium > Sodium > Calcium > Magnesium > Aluminium > (Carbon) > Zinc > Iron > Lead > (Hydrogen) > Copper > Silver > Gold
钾 > 钠 > 钙 > 镁 > 铝 > (碳) > 锌 > 铁 > 铅 > (氢) > 铜 > 银 > 金
solution of a less reactive metal. Example: zinc + copper sulfate → zinc sulfate + copper.
将一种较活泼的金属放入较不活泼金属的盐溶液中，会发生置换反应。示例：锌 + 硫酸铜 → 硫酸锌 + 铜。
9. Rate of Reaction | 反应速率
The rate of a chemical reaction measures how quickly reactants are used up or products are formed.
化学反应速率衡量反应物消耗或生成物生成的快慢程度。
Rate of reaction = Change in amount (or concentration) of reactant or product ÷ Time taken
反应速率 = 反应物或生成物的（质量/浓度）变化量 ÷ 所用时间
Factors that increase the rate: higher temperature, greater concentration of solutions, larger surface area of solids, and the presence of a catalyst. Collision theory explains these effects: successful collisions must occur with enough energy (activation energy) and proper orientation.
加快反应速率的因素：升高温度、增大溶液浓度、增大固体表面积、使用催化剂。碰撞理论解释了这些影响：必须发生具有足够能量（活化能）和正确取向的有效碰撞。
10. Separation Techniques Principles | 分离技术原理
Mixtures can be separated by physical means, relying on differences in physical properties.
混合物可通过物理方法分离，利用的是各组分物理性质的差异。
- Filtration 过滤： Used to separate an insoluble solid from a liquid. Based on particle size. 用于分离不溶性固体与液体，基于颗粒大小。
- Crystallisation / Evaporation 结晶/蒸发： Separates a soluble solid from a solution by evaporating the solvent. 通过蒸发溶剂从溶液中分离可溶性固体。
- Simple distillation 简单蒸馏： Separates a solvent from a solution; the solvent vapour is condensed and collected. 用于从溶液中分离溶剂，溶剂蒸气冷凝回收。
- Fractional distillation 分馏： Separates two or more liquids with different boiling points. 用于分离沸点不同的两种或多种液体。
- Paper chromatography 纸色谱： ty in a solvent. Rf value = distance moved by substance ÷ distance moved by solvent front. 基于不同物质在溶剂中溶解度的差异分离有色物质。Rf 值 = 物质移动距离 ÷ 溶剂前沿移动距离。
The Rf value is a ratio used to identify components in a mixture. Each pure substance has a characteristic Rf under given conditions.
Rf 值是用来鉴定混合物组分的比值。在给定条件下，每种纯物质都有其特定的 Rf 值。
11. Periodic Table Patterns | 元素周期表规律
The modern periodic table arranges elements in order of increasing atomic number. Periods are horizontal rows; groups are vertical columns containing elements with similar chemical properties.
现代周期表按原子序数递增的顺序排列元素。横行称为周期，纵列称为族，同一族的元素具有相似的化学性质。
Group 1 (alkali metals): one electron in outer shell, very reactive, reactivity increases down the group. Group 7 (halogens): seven electrons in outer shell, reactive non‑metals, reactivity decreases down the group. Group 0 (noble gases): full outer shell, unreactive.
第 1 族（碱金属）：最外层有 1 个电子，非常活泼，活泼性从上到下递增。第 7 族（卤素）：最外层有 7 个电子，活泼的非金属，活泼性从上到下递减。第 0 族（稀有气体）：最外层全满，极不活泼。
Number of outer electrons = group number (for Groups 1–2 and 13–18 after subtracting 10)
最外层电子数 = 族序数（第 1–2 族和 第 13–18 族需减 10）
Metals are found on the left and centre of the table; non‑metals on the right. The staircase line separates them.
金属位于周期表的左侧和中部，非金属位于右侧。阶梯线将它们隔开。
12. Bonding Types & Properties | 键合类型与性质
Atoms join together to achieve a full outer shell. Three main types of strong chemical bonding are studied: ionic, covalent, and metallic.
原子结合是为了达到稳定满壳层结构。主要学习三种强化学键：离子键、共价键和金属键。
- Ionic bonding 离子键： Transfer of electrons from metal to non‑metal; oppositely charged ions held together by electrostatic attraction. Giant ionic lattices have high melting points and conduct electricity when molten or dissolved. 金属向非金属转移电子；带相反电荷的离子通过静电力结合。巨型离子晶格具有高熔点，熔融或溶解时能导电。
- Covalent bonding 共价键： Sharing of electrons between non‑metal atoms. Simple molecular substances (e.g., H₂O, CO₂) have low melting points and do not conduct electricity; giant covalent structures (e.g., diamond, SiO₂) have very high melting points. 非金属原子之间共享电子。简单分子物质（如 H₂O, CO₂）熔点低、不导电；巨型共价结构（如金刚石, SiO₂）熔点极高。
- Metallic bonding 金属键： Positive metal ions in a ‘sea’ of delocalised electrons. This explains why metals conduct electricity, are malleable, and ductile. 金属阳离子沉浸在“离域电子海”中。这解释了金属的导电性、延展性和展性。
Properties such as melting point, boiling point, and electrical conductivity are directly linked to the structure and bonding of a substance.
熔点、沸点和导电性等性质直接与物质的结构和键合方式相关。
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