📚 Year 7 Cambridge Chemistry: Formula & Theorem Quick-Reference Handbook | Year 7 Cambridge 化学：公式定理速查手册
Welcome to your Year 7 Cambridge Chemistry formula and theorem handbook. This concise guide brings together every important rule, definition, law and equation you need to master during the Lower Secondary checkpoint stage. Use it to quickly look up the particle theory, learn how to write chemical formulae, balance equations, understand acids and alkalis, and apply the density formula. Each section presents key facts in clear English first, followed immediately by simplified Chinese, so you can build deep bilingual understanding. Keep it handy while studying or revising – it will help you answer questions confidently and link concepts together.
欢迎使用你的 Year 7 Cambridge 化学公式定理速查手册。这本简明手册汇集了你在初中阶段必须掌握的所有重要规则、定义、定律和方程式。你可以用它快速查阅粒子理论、学习书写化学式、配平方程式、理解酸碱性质以及应用密度公式。每个部分先用清晰的英文呈现关键知识点，紧接着用通俗的中文解释，帮助你建立扎实的双语理解。无论是日常学习还是考前复习，这本手册都能帮你自信答题、串联概念。
1. Particle Theory of Matter | 物质粒子理论
The Particle Theory of Matter states that all substances are made of tiny, constantly moving particles with empty spaces between them, and raising the temperature increases their kinetic energy.
物质粒子理论指出：所有物质都由微小的粒子构成，这些粒子永不停息地运动，粒子之间存在空隙，升高温度会增加粒子的动能。
This theory provides the foundation for understanding states of matter, diffusion and changes of state. It explains why solids keep a fixed shape (particles vibrate in fixed positions), liquids flow and take the shape of a container (particles can slide past each other), and gases spread out to fill any space (particles move rapidly and far apart).
这一理论是理解物质状态、扩散和状态变化的基础。它解释了为什么固体能保持固定形状（粒子在固定位置上振动），液体可以流动并随容器改变形状（粒子可以相互滑动），气体能充满整个空间（粒子快速运动且相距很远）。
Solid: particles vibrate in fixed positions – strong forces of attraction, definite shape and volume.
固体：粒子在固定位置上振动——粒子间作用力强，有确定的形状和体积。
Liquid: particles can move around but remain close – weaker forces, definite volume but no definite shape.
液体：粒子可以移动但间距仍较小——作用力较弱，有确定的体积但没有确定的形状。
Gas: particles move fast and are far apart – very weak forces, no definite shape or volume.
气体：粒子快速运动且间距很大——作用力极微弱，没有确定的形状和体积。
2. States of Matter and Their Changes | 物质状态及其变化
Changes of state are physical changes, not chemical changes. During a change of state, the temperature remains constant while the substance absorbs or releases energy as latent heat. The six key transitions are melting, freezing, boiling (vaporisation), condensation, sublimation and deposition.
状态变化是物理变化，不是化学变化。在状态变化过程中，物质吸收或释放潜热，温度保持恒定。六种主要的转变过程是熔化、凝固、汽化（沸腾）、冷凝、升华和凝华。
solid ⇌ liquid (melting / freezing)
固体 ⇌ 液体（熔化/凝固）
liquid ⇌ gas (vaporisation / condensation)
液体 ⇌ 气体（汽化/冷凝）
solid → gas (sublimation), gas → solid (deposition)
固体 → 气体（升华），气体 → 固体（凝华）
The melting point and boiling point are physical properties that can be used to identify pure substances. Impurities lower the melting point and raise the boiling point.
熔点和沸点是可用于识别纯净物的物理性质。杂质会降低熔点并升高沸点。
3. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance made of only one type of atom. A compound is a pure substance made of two or more different elements chemically bonded in a fixed ratio. A mixture contains two or more substances not chemically combined, and the composition can vary.
元素是由同一种原子组成的纯净物。化合物是由两种或多种不同元素以固定比例通过化学键结合而成的纯净物。混合物包含两种或多种没有发生化学结合的物质，并且组成比例可以变化。
Key theorem: The Law of Constant Composition (Definite Proportions) states that a given chemical compound always contains its component elements in a fixed mass ratio.
重要定理：定比定律指出，任何给定的化合物总是以其组成元素固定的质量比存在。
For example, pure water H₂O always has 2 hydrogen atoms bonded to 1 oxygen atom, and the mass ratio of hydrogen to oxygen is always 1 : 8. In contrast, salt water is a mixture; you can add different amounts of salt to water.
例如，纯水 H₂O 中总是2个氢原子与1个氧原子结合，氢与氧的质量比恒为1:8。而盐水是一种混合物，你可以向水中加入不同量的盐。
Separation techniques such as filtration, evaporation, distillation and chromatography are used to separate mixtures into their components. Compounds can only be broken down by chemical reactions.
分离技术如过滤、蒸发、蒸馏和色谱法用于把混合物分离成各组分。化合物只有通过化学反应才能分解。
4. Chemical Symbols, Formulae and Naming | 化学符号、化学式与命名
Every element has a unique chemical symbol, usually one or two letters, with the first letter always capitalised. The formula of a compound shows the symbols of the elements present and the ratio of atoms using subscript numbers.
每种元素都有唯一的化学符号，通常为一或两个字母，第一个字母始终大写。化合物的化学式用元素符号表示所含元素，并用下标数字表示原子的个数比。
Valency (combining power) is the number of chemical bonds an atom of an element can form. In ionic compounds, the total positive charge must equal the total negative charge.
化合价（结合能力）是一个元素的原子所能形成的化学键数目。在离子化合物中，正负电荷总数必须相等。
To write a formula for an ionic compound, use the ‘cross-over’ method: write the symbols with their valencies as superscripts, cross over the numbers to become subscripts, and simplify if possible.
书写离子化合物的化学式时，可使用“交叉法”：写出带化合价（上标）的元素符号，将价数交叉作为对方的下标，然后尽可能约简。
Example: aluminium oxide. Al³⁺ and O²⁻ → Al₂O₃.
示例：氧化铝。Al³⁺ 和 O²⁻ → Al₂O₃。
General rule: (charge of A) × (number of A atoms) + (charge of B) × (number of B atoms) = 0
一般规则：(A的电荷) × (A的原子数) + (B的电荷) × (B的原子数) = 0
Naming rules: metal + non-metal compound – the metal name comes first, and the non-metal name changes to end in ‘-ide’. When two non-metals combine, prefixes (mono-, di-, tri-) indicate the number of atoms.
命名规则：金属与非金属形成的化合物——金属名在前，非金属名称以“-化某”结尾。两个非金属结合时，使用前缀（一、二、三）表示原子个数。
Common valencies: H: +1, O: -2, Na: +1, Cl: -1, Mg: +2, Al: +3, Cu: +2, Fe: +2/+3, OH: -1, SO₄: -2, NO₃: -1, CO₃: -2.
常见化合价：H: +1, O: -2, Na: +1, Cl: -1, Mg: +2, Al: +3, Cu: +2, Fe: +2/+3, OH: -1, SO₄: -2, NO₃: -1, CO₃: -2。
5. Law of Conservation of Mass | 质量守恒定律
The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of the reactants always equals the total mass of the products.
质量守恒定律指出，在化学反应中，物质既不会被创造也不会被消灭。反应物的总质量总是等于生成物的总质量。
This law is the fundamental principle behind balancing chemical equations. All atoms present at the start must be present at the end, simply rearranged. If a reaction is carried out in a closed container, the mass remains unchanged before and after the reaction.
这条定律是配平化学方程式的基本原理。反应开始时存在的所有原子，在反应结束时仍然存在，只是重新组合了。若在密闭容器中发生反应，反应前后的总质量保持不变。
For reactions that appear to lose mass (e.g. when a gas escapes), the mass is not destroyed; it simply leaves the reaction vessel. A balanced equation always respects conservation of mass.
对于一些看似质量减少的反应（例如有气体逸出），质量并未被消灭，只是离开了反应容器。配平的方程式始终遵守质量守恒。
6. Writing and Balancing Chemical Equations | 书写和配平化学方程式
A word equation uses the names of reactants and products. A symbol equation uses chemical formulae and must be balanced.
文字表达式使用反应物和生成物的名称。符号表达式使用化学式且必须配平。
General form: reactant(s) → product(s)
一般形式：反应物 → 生成物
To balance an equation, follow these steps: write the correct formula for each substance; count the atoms of each element on both sides; add big numbers (coefficients) in front of formulae to make the number of each type of atom equal on both sides; never change the small subscript numbers inside a formula.
配平方程式的步骤：写出每种物质的正确化学式；数出两边每种元素的原子数目；在化学式前添加大数字（系数），使两边每种原子的总数相等；绝不能改变化学式中的下标小数字。
Example: hydrogen + oxygen → water. Unbalanced: H₂ + O₂ → H₂O. Balanced: 2H₂ + O₂ → 2H₂O.
示例：氢气+氧气→水。未配平：H₂ + O₂ → H₂O。配平后：2H₂ + O₂ → 2H₂O。
Check: left side has 4 H atoms and 2 O atoms; right side 2 × H₂O gives 4 H and 2 O. Mass is conserved.
检验：左边有4个氢原子、2个氧原子；右边2个水分子给出4个氢原子、2个氧原子，质量守恒。
State symbols are often added in brackets: (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved in water).
通常还会在括号里加上状态符号：(s)固体，(l)液体，(g)气体，(aq)水溶液。
2H₂(g) + O₂(g) → 2H₂O(l)
7. Acids, Alkalis and the pH Scale | 酸、碱和pH标度
An acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. An alkali is a soluble base that releases hydroxide ions (OH⁻) in water. The pH scale measures how acidic or alkaline a solution is, ranging from 0 to 14.
酸是在水中能释放出氢离子（H⁺）的物质。碱是能释放氢氧根离子（OH⁻）的可溶性碱。pH标度用于衡量溶液的酸碱度，范围从0到14。
pH < 7: acidic (more H⁺), pH = 7: neutral (pure water), pH > 7: alkaline (more OH⁻).
pH < 7：酸性（H⁺较多），pH = 7：中性（纯水），pH > 7：碱性（OH⁻较多）。
The pH value can be found using universal indicator, litmus paper, or a pH meter. Litmus turns red in acidic solutions and blue in alkaline solutions. Universal indicator gives a range of colours: red/orange/yellow (acid), green (neutral), blue/purple (alkaline).
pH值可用通用指示剂、石蕊试纸或pH计测定。石蕊在酸性溶液中变红，在碱性溶液中变蓝。通用指示剂显示一系列颜色：红/橙/黄（酸），绿（中性），蓝/紫（碱性）。
Every time you go down one unit on the pH scale, the hydrogen ion concentration increases by a factor of 10. This is a logarithmic relationship, though at Year 7 you mainly learn the colour scale.
pH标度每下降一个单位，氢离子浓度就增加10倍，这是一种对数关系，不过在Year 7阶段你主要学习颜色标度。
8. Neutralisation Reaction | 中和反应
Neutralisation is the reaction between an acid and a base (or alkali) to produce a salt and water. It is an important type of double displacement reaction and can be represented by a general word equation.
中和反应是酸与碱（或可溶性碱）作用生成盐和水的反应。它是一种重要的复分解反应，可用通式表示。
acid + base → salt + water
酸 + 碱 → 盐 + 水
The net ionic equation for neutralisation between a strong acid and a strong alkali is always:
强酸与强碱中和反应的离子方程式总是：
H⁺ + OH⁻ → H₂O
Example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
示例：盐酸 + 氢氧化钠 → 氯化钠 + 水。
HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
The salt produced depends on the acid used: hydrochloric acid gives chlorides, sulfuric acid gives sulfates, nitric acid gives nitrates. Neutralisation has many applications, such as treating acidic soil with lime (calcium oxide) and relieving indigestion with antacids.
生成的盐取决于所用酸的种类：盐酸产生氯化物，硫酸产生硫酸盐，硝酸产生硝酸盐。中和反应用于许多实际场合，如用石灰（氧化钙）处理酸性土壤以及用抗酸药缓解胃灼热。
9. Indicators and Their Colour Changes | 指示剂及其颜色变化
An indicator is a substance that changes colour depending on the pH of the solution. Common indicators used in the Year 7 chemistry lab include litmus, methyl orange and phenolphthalein.
指示剂是一种会根据溶液pH值改变颜色的物质。Year 7化学实验室常用的指示剂包括石蕊、甲基橙和酚酞。
| Indicator | Acidic colour | Neutral colour | Alkaline colour |
|---|---|---|---|
| Litmus | Red | Purple | Blue |
| Methyl orange | Red | Orange | Yellow |
| Phenolphthalein | Colourless | Colourless | Pink |
Universal indicator is a mixture of several indicators and shows a full spectrum of colours from pH 1 to 14. You should be able to estimate the pH of a solution by matching the colour to a pH colour chart.
通用指示剂是几种指示剂的混合物，能够显示从pH 1到14的全谱颜色。你应该学会将颜色与pH比色卡比对，估算溶液的pH值。
When carrying out a titration, an indicator is used to signal the neutralisation endpoint where the colour changes sharply. Choosing the right indicator depends on the strength of the acid and base used.
进行滴定实验时，指示剂用于指示中和终点，此时颜色发生突变。选择合适的指示剂取决于所用酸和碱的强弱。
10. Density and Physical Properties Formula | 密度与物理性质公式
Density is a physical property of a substance that describes how much mass is packed into a given volume. It is often used to identify materials and to predict whether an object will sink or float in water.
密度是物质的一种物理性质，描述单位体积内所含质量的大小。它常用于鉴定材料以及预判物体在水中会下沉还是上浮。
Density = mass ÷ volume
密度 = 质量 ÷ 体积
d = m / V
Units: mass in grams (g) or kilograms (kg); volume in cubic centimetres (cm³) or cubic metres (m³). Common units of density are g/cm³ or kg/m³. For water, the density at 4 °C is 1.0 g/cm³.
单位：质量用克（g）或千克（kg）；体积用立方厘米（cm³）或立方米（m³）。密度的常用单位是 g/cm³ 或 kg/m³。水在4°C时的密度为1.0 g/cm³。
Objects with density less than 1.0 g/cm³ float in water;
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