📚 Year 7 CAIE Chemistry: Quick Reference Handbook of Formulas and Theorems | Year 7 CAIE 化学：公式定理速查手册
This quick reference handbook brings together the essential formulas, definitions and key concepts from the Year 7 CAIE Chemistry syllabus. Use it to review states of matter, atomic structure, chemical formulae, reaction patterns and separation methods. Every statement is kept concise and exam‑focused so you can find the rules you need quickly.
本速查手册汇集了 Year 7 CAIE 化学课程中的核心公式、定义和重要概念。你可以用它复习物质状态、原子结构、化学式、反应规律和分离方法。每一条说明都力求简洁、贴近考试要求，方便你在需要时快速找到对应的原理。
1. States of Matter and Change of State | 物质状态与状态变化
Matter exists in three main states: solid, liquid and gas. The particle model explains their properties. In solids, particles are packed closely in a fixed arrangement and can only vibrate. In liquids, particles are close together but can move past one another. In gases, particles are far apart and move freely at high speed.
物质以三种主要状态存在：固态、液态和气态。粒子模型可以解释它们的性质。固态时，粒子紧密排列在固定位置上，只能振动。液态时，粒子彼此靠近但可以相互滑动。气态时，粒子相距很远，高速自由运动。
The changes of state are physical changes. When a solid is heated, it melts into a liquid at its melting point. When a liquid is heated, it boils into a gas at its boiling point. The reverse processes are freezing (liquid to solid) and condensation (gas to liquid). Sublimation is the direct change from solid to gas, and deposition is the reverse.
状态变化属于物理变化。固体加热到熔点会熔化成液体；液体加热到沸点会沸腾变成气体。相反的过程是凝固（液体变固体）和冷凝（气体变液体）。升华是固体直接变为气体，凝华则是相反的过程。
Solid ⇌ Liquid (melting / freezing) | Liquid ⇌ Gas (boiling / condensation) | Solid ⇌ Gas (sublimation / deposition)
2. Atomic Structure and the Periodic Table | 原子结构与元素周期表
An atom consists of a tiny, dense nucleus containing protons and neutrons, surrounded by electrons arranged in shells. Protons carry a positive charge (+1), neutrons are neutral (0), and electrons carry a negative charge (−1). In a neutral atom, the number of protons equals the number of electrons.
原子由一个极小且致密的原子核（含有质子和中子）以及核外分层排布的电子构成。质子带一个正电荷（+1），中子不带电（0），电子带一个负电荷（−1）。在中性原子中，质子数等于电子数。
The atomic number (Z) is the number of protons in the nucleus. It defines the element. The mass number (A) is the total number of protons and neutrons. The number of neutrons can be found by subtracting Z from A. Electrons fill shells in the pattern 2, 8, 8 … for the first 20 elements.
原子序数（Z）是原子核内质子数，决定了元素的种类。质量数（A）是质子与中子数之和。中子数 = A − Z。前20号元素的核外电子按 2、8、8…… 的规律分层排布。
The Periodic Table arranges elements in order of increasing atomic number. Rows are called periods; the period number equals the number of occupied electron shells. Columns are called groups; elements in the same group have the same number of outer‑shell electrons and therefore similar chemical properties.
元素周期表按原子序数递增的顺序排列元素。横排称为周期，周期数等于电子层数。竖列称为族，同族元素的最外层电子数相同，因此具有相似的化学性质。
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. It cannot be broken down into simpler substances by chemical means. A compound is a pure substance made of two or more different elements chemically combined 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.
元素是由同种原子组成的纯净物，无法通过化学方法分解为更简单的物质。化合物是由两种或多种不同元素按照固定比例化合而成的纯净物。混合物则由两种或多种物质（元素或化合物）简单混合而成，它们没有发生化学结合，可以用物理方法分离。
Compounds have properties different from the elements that make them. For example, sodium chloride (NaCl) is a white, safe‑to‑eat solid, but sodium is a highly reactive metal and chlorine is a poisonous gas. Mixtures retain the properties of their individual components.
化合物的性质与组成它的元素不同。例如，氯化钠（NaCl）是一种白色、可食用的固体，而钠是极活泼的金属，氯是有毒气体。混合物中各组分保持各自原有的性质。
4. Chemical Symbols and Formulae | 化学符号与化学式
Each element is represented by a one‑ or two‑letter symbol. The first letter is always upper case and the second, if present, is lower case. Examples: C for carbon, O for oxygen, Na for sodium, Fe for iron. A chemical formula shows the types and numbers of atoms in a compound. The subscript after a symbol indicates how many atoms of that element are present; no subscript means one atom.
每种元素用一个或两个字母的符号表示。首字母大写，如果有第二个字母则小写。例如：C 代表碳，O 代表氧，Na 代表钠，Fe 代表铁。化学式表明化合物中原子的种类和数量。元素符号右下角的数字表示该原子的个数，没有数字则代表 1 个原子。
Writing formulae uses the principle of valency: atoms combine so that the total positive charge equals the total negative charge. For simple ionic compounds, the charges of the ions are swapped to become subscripts. For example, calcium Ca²⁺ and chloride Cl⁻ give CaCl₂.
书写化学式遵循化合价规则：原子结合时，正负总电荷数相等。对于简单离子化合物，离子所带电荷数交叉作为角标。例如钙离子 Ca²⁺ 与氯离子 Cl⁻ 结合时得到 CaCl₂。
Common valencies: Group 1 = +1, Group 2 = +2, Group 13 = +3, Group 15 = −3, Group 16 = −2, Group 17 = −1.
5. 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 the mass of a carbon‑12 atom. It has no units. For most elements, Aᵣ is close to the mass number. You can find Aᵣ values on the Periodic Table.
相对原子质量（Aᵣ）是一个元素的原子平均质量与 1/12 个碳‑12 原子质量的比值，没有单位。大多数元素的 Aᵣ 值接近其质量数。相对原子质量可在元素周期表中查到。
The relative molecular mass (Mᵣ) is the sum of the relative atomic masses of all the atoms in a molecule. It is calculated by multiplying each atom’s Aᵣ by its subscript and adding the results.
相对分子质量（Mᵣ）是分子中所有原子的相对原子质量之和。计算方法是：将每种原子的 Aᵣ 乘以其角标数，然后将各项相加。
Mᵣ of H₂O = (2 × 1) + (1 × 16) = 18 | Mᵣ of CO₂ = (1 × 12) + (2 × 16) = 44
6. Conservation of Mass and Balancing Equations | 质量守恒与方程式配平
The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of reactants always equals the total mass of products. This is why chemical equations must be balanced.
质量守恒定律指出，在化学反应中，质量既不会凭空产生也不会凭空消失。反应物的总质量始终等于生成物的总质量。因此化学方程式必须配平。
A balanced equation has the same number of each type of atom on both sides of the arrow. Coefficients (large numbers placed before a formula) are used to balance the atoms. Subscripts inside a formula must never be changed when balancing.
配平的方程式要求箭头两边每种原子的个数相等。用化学式前的系数（大数字）来配平原子数。配平时绝对不能改变化学式右下角的角标。
Unbalanced: H₂ + O₂ → H₂O
Balanced: 2H₂ + O₂ → 2H₂O
7. Acids, Bases and the pH Scale | 酸、碱与 pH 标度
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They taste sour, turn blue litmus red, and have pH values less than 7. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
酸是溶于水时释放出氢离子（H⁺）的物质。它们有酸味，能使蓝色石蕊试纸变红，pH 值小于 7。实验室常见的酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。
Bases are substances that neutralise acids. Alkalis are soluble bases that release hydroxide ions (OH⁻) in water. They feel slippery, turn red litmus blue, and have pH values greater than 7. Examples include sodium hydroxide (NaOH) and potassium hydroxide (KOH).
碱是能中和酸的物质。可溶性碱（碱溶液）在水中释放氢氧根离子（OH⁻）。它们手感滑腻，能使红色石蕊试纸变蓝，pH 值大于 7。例子有氢氧化钠（NaOH）和氢氧化钾（KOH）。
The pH scale (0–14) measures how acidic or alkaline a solution is. pH 7 is neutral (pure water). Universal indicator shows a range of colours across the pH scale, from red (strong acid) through green (neutral) to purple (strong alkali).
pH 标度（0–14）用于衡量溶液的酸碱程度。pH 7 为中性（纯水）。通用指示剂在 pH 标度上呈现一系列颜色，从红色（强酸）经绿色（中性）到紫色（强碱）。
8. Neutralisation Reactions | 中和反应
Neutralisation is the reaction between an acid and a base to form a salt and water. The hydrogen ions from the acid react with hydroxide ions from the alkali to produce water molecules, while the remaining ions form the salt.
中和反应是酸与碱反应生成盐和水的反应。酸中的氢离子与碱中的氢氧根离子结合生成水分子，剩余的离子则构成盐。
Acid + Alkali → Salt + Water
HCl + NaOH → NaCl + H₂O
H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
Acids also react with metal carbonates to produce a salt, water and carbon dioxide gas. This is another form of neutralisation and can be used to test for carbonates.
酸也可以与金属碳酸盐反应，生成盐、水和二氧化碳气体。这是另一种形式的中和反应，可用于检验碳酸盐。
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
9. Properties of Metals and Non‑metals | 金属与非金属的性质
Metals are found on the left side and centre of the Periodic Table. They are typically shiny, good conductors of heat and electricity, malleable (can be hammered into shape) and ductile (can be drawn into wires). Most metals are solid at room temperature (mercury is an exception).
金属位于周期表的左侧和中间。它们通常有光泽，是热和电的良导体，具有延展性（可锤打成形）和韧性（可拉成丝）。大多数金属在室温下是固体（汞除外）。
Non‑metals appear on the right side of the Periodic Table. They are poor conductors, often dull, and brittle when solid. They have lower melting and boiling points than most metals. Many non‑metals are gases at room temperature, such as oxygen, nitrogen and chlorine.
非金属位于周期表的右侧。它们通常是热和电的不良导体，没有光泽，固态时质脆。它们的熔点和沸点低于大多数金属。许多非金属在室温下是气体，如氧气、氮气和氯气。
Metal oxides are usually basic; they neutralise acids to form a salt and water. Non‑metal oxides are usually acidic; they dissolve in water to form acids and neutralise alkalis.
金属氧化物通常是碱性的，能与酸中和生成盐和水。非金属氧化物通常是酸性的，能溶于水形成酸，并能中和碱。
10. Simple Chemical Reactions | 简单的化学反应
When a metal reacts with oxygen, a metal oxide is formed. This is an oxidation reaction. The general equation is:
金属与氧气反应生成金属氧化物，属于氧化反应。通用方程式为：
Metal + Oxygen → Metal Oxide | 2Mg + O₂ → 2MgO
When a metal reacts with an acid, a salt and hydrogen gas are produced. The metal displaces hydrogen from the acid. The test for hydrogen is a lighted splint, which gives a ‘squeaky pop’.
金属与酸反应生成盐和氢气。金属把酸中的氢置换出来。氢气的检验方法是用点燃的木条放在管口，会发出“噗”的一声（爆鸣）。
Metal + Acid → Salt + Hydrogen | Zn + 2HCl → ZnCl₂ + H₂
When a metal carbonate reacts with an acid, a salt, water and carbon dioxide are formed. Carbon dioxide turns limewater milky (cloudy).
金属碳酸盐与酸反应生成盐、水和二氧化碳。二氧化碳能使石灰水变浑浊。
Metal Carbonate + Acid → Salt + Water + Carbon Dioxide | CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
Combustion (burning) is a rapid reaction with oxygen that releases heat and light. Fuels such as hydrocarbons burn to produce carbon dioxide and water when oxygen supply is plentiful.
燃烧是与氧气的快速反应，释放出热和光。在氧气充足的条件下，碳氢化合物等燃料燃烧生成二氧化碳和水。
11. Separation Techniques | 分离技术
Different separation methods are chosen based on the physical properties of the substances in a mixture. The table below summarises the main techniques required for Year 7.
分离方法的选择取决于混合物中各物质的物理性质。下表总结了 Year 7 需要掌握的主要分离技术。
| Technique (English) | 技术（中文） | Used to separate | 用于分离 |
|---|---|---|---|
| Filtration | 过滤 | An insoluble solid from a liquid | 不溶性固体与液体 |
| Evaporation | 蒸发 | A dissolved solid from a solution | 从溶液中分离溶解的固体 |
| Simple distillation | 简单蒸馏 | A liquid from a solution (or two liquids with very different boiling points) | 从溶液中分离液体（或沸点相差很大的两种液体） |
| Chromatography | 色谱法 | Different soluble coloured substances | 不同可溶性有色物质 |
In filtration, the mixture is poured through filter paper in a funnel. The solid (residue) stays on the paper and the liquid (filtrate) passes through. In evaporation, the solution is heated so the solvent evaporates, leaving the solute behind as crystals. Distillation involves boiling the liquid and condensing the vapour back into a pure liquid in a separate container.
过滤时，混合物倒入装有滤纸的漏斗中。固体（残渣）留在滤纸上，液体（滤液）通过滤纸。蒸发时，加热溶液使溶剂蒸发，留下溶质晶体。蒸馏则是将液体煮沸，然后把蒸气冷凝到另一个容器中，得到纯净液体。
12. Gas Tests | 气体检验
Identifying common gases is an important practical skill. The following table lists the standard tests for oxygen, hydrogen and carbon dioxide, along with the positive results.
鉴别常见气体是一项重要的实验技能。下表列出了氧气、氢气和二氧化碳的标准检验方法及阳性结果。
| Gas (English) | 气体（中文） | Test | 检验方法 | Positive result | 阳性结果 |
|---|---|---|---|---|---|
| Oxygen (O₂) | 氧气 | Glowing splint | 带火星的木条 | Splint relights | 木条复燃 |
| Hydrogen (H₂) | 氢气 | Lighted splint | 点燃的木条 | Squeaky pop sound | 发出爆鸣声 |
| Carbon dioxide (CO₂) | 二氧化碳 | Bubble through limewater | 通入石灰水 | Limewater turns milky (cloudy) | 石灰水变浑浊 |
Always record the initial appearance of the reagent (e.g. clear, colourless limewater) and the change observed. The limewater test is also used to confirm the presence of carbon dioxide in respiration and combustion reactions.
务必记录试剂最初的外观（例如澄清、无色的石灰水）以及观察到的变化。石灰水检验也可用于确认呼吸作用和燃烧反应中生成的二氧化碳。
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