📚 Year 7 CIE Chemistry: Formula & Theorem Quick Reference Handbook | Year 7 CIE 化学：公式定理速查手册
Welcome to the Year 7 CIE Chemistry Formula & Theorem Quick Reference Handbook. This guide compiles all the essential formulas, rules, and key principles you need to master for your Checkpoint and beyond. Each section provides clear definitions, worked examples, and useful tips to help you recall important concepts during revision and exams.
欢迎使用 Year 7 CIE 化学公式定理速查手册。本手册汇编了你在 Checkpoint 及后续学习中需要掌握的所有基本公式、规则和关键原理。每个部分都提供了清晰的定义、示例和实用提示，帮助你复习和巩固重要概念。
1. States of Matter and Particle Theory | 物质状态与粒子理论
All matter is composed of tiny particles that are in constant motion. The arrangement and movement of these particles determine whether a substance is a solid, a liquid or a gas.
所有物质都由处于不停运动中的微小粒子组成。这些粒子的排列方式和运动情况决定了物质是固体、液体还是气体。
In solids, particles are tightly packed in a regular pattern and can only vibrate in fixed positions. In liquids, particles are close together but can slide past one another, so liquids flow and take the shape of their container. In gases, particles are far apart and move rapidly in all directions, filling any available space.
在固体中，粒子紧密堆积，排列规则，只能在固定位置上振动。在液体中，粒子相互靠近但可以滑动，因此液体会流动并呈现容器的形状。在气体中，粒子相距很远并快速向各个方向运动，会充满任何可用的空间。
ling point, condensation (gas → liquid), freezing (liquid → solid) and sublimation (solid → gas directly). During a change of state, the temperature remains constant while the particles gain or lose energy to overcome forces of attraction.
状态变化属于物理变化：熔化（固体 → 液体）发生在熔点，沸腾或蒸发（液体 → 气体）发生在沸点，冷凝（气体 → 液体），凝固（液体 → 固体）以及升华（固体直接变为气体）。在状态变化过程中，温度保持恒定，粒子吸收或失去能量以克服吸引力。
2. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance made up of only one type of atom. Elements are listed on the Periodic Table and cannot be broken down into simpler substances by chemical means.
元素是由同一种原子组成的纯净物。元素列在周期表中，无法通过化学方法分解成更简单的物质。
A compound is a pure substance formed when two or more elements chemically combine in fixed proportions. The properties of a compound are completely different from the elements it contains. For example, water (H₂O) is a liquid, whereas hydrogen and oxygen are gases.
化合物是由两种或两种以上元素以固定比例通过化学结合而成的纯净物。化合物的性质与其所含元素完全不同。例如，水（H₂O）是液体，而氢和氧是气体。
A mixture consists of two or more substances (elements or compounds) that are physically mixed but not chemically joined. Mixtures do not have a fixed composition and can be separated by physical methods such as filtration, distillation or chromatography.
混合物由两种或两种以上的物质（元素或化合物）通过物理方式混合而成，并未发生化学结合。混合物没有固定的组成，可以通过过滤、蒸馏或色谱等物理方法进行分离。
3. Atomic Structure | 原子结构
Atoms are the smallest particles of an element that can take part in a chemical reaction. Every atom contains a central nucleus made of protons and neutrons, surrounded by electrons orbiting in shells.
原子是元素中能参与化学反应的最小粒子。每个原子都有一个由质子和中子组成的中央核，核外是分层排布的电子。
er (A) is the total number of protons and neutrons in the nucleus: A = number of protons + number of neutrons.
原子中质子的数目称为原子序数（Z）。在中性原子中，电子数等于质子数。质量数（A）是原子核内质子数和中子数的总和：质量数 = 质子数 + 中子数。
Electrons occupy specific energy levels (shells). The first shell can hold up to 2 electrons, the second up to 8 electrons, and the arrangement determines the chemical reactivity of the element. Ions form when atoms gain or lose electrons, resulting in a charged particle.
电子占据特定的能级（电子层）。第一层最多容纳 2 个电子，第二层最多容纳 8 个电子，电子排布决定了元素的化学活泼性。当原子得到或失去电子时，会形成带电的离子。
4. The Periodic Table | 元素周期表
The Periodic Table organises all known elements in order of increasing atomic number. Elements are arranged into vertical columns called groups and horizontal rows called periods.
元素周期表按原子序数递增的顺序排列所有已知元素。元素排列成纵列（族）和横行（周期）。
Elements in the same group have the same number of electrons in their outer shell, which gives them similar chemical properties. For Groups 1, 2 and 13 to 18, the group number equals the number of outer-shell electrons. The period number tells you how many electron shells an atom has.
同一族的元素具有相同的最外层电子数，因此化学性质相似。对于第 1、2 族和第 13 至 18 族，族数等于最外层电子数。周期数代表原子具有的电子层数。
Metals are found on the left side of the table and non-metals on the right. Elements in Group 1 (alkali metals) are very reactive, while Group 18 (noble gases) are unreactive because they have full outer shells.
金属位于周期表左侧，非金属位于右侧。第 1 族（碱金属）元素非常活泼，而第 18 族（稀有气体）元素因为拥有全满的最外层电子，很不活泼。
5. Chemical Symbols and Formulae | 化学符号与化学式
Each element is represented by a unique chemical symbol, consisting of one or two letters. The first letter is always capitalised and the second, if present, is in lower case. Examples include H for hydrogen, O for oxygen, Na for sodium and Fe for iron.
每种元素用一个独特的化学符号表示，由一或两个字母组成。第一个字母总是大写，如果有第二个字母则用小写。例如 H 表示氢，O 表示氧，Na 表示钠，Fe 表示铁。
A chemical formula shows the types and numbers of atoms present in a compound. Subscript numbers indicate how many atoms of each element are in one unit of the compound; no subscript means one atom. The metal or positive ion is written first. Common formulae: H₂O, CO₂, NaCl, CaCO₃, H₂SO₄ and CH₄.
化学式表示化合物中存在的原子的种类和数量。下标数字表示每个单元中该元素原子的个数；没有下标则表示 1 个原子。金属或阳离子写在前面。常见化学式：H₂O、CO₂、NaCl、CaCO₃、H₂SO₄ 和 CH₄。
When writing formulae from compound names, you must use the correct symbols and know the combining powers (valencies). For simple ionic compounds, swap the valency numbers and write them as subscripts, then cancel down if needed.
根据名称书写化学式时，必须使用正确的符号并了解化合价。对于简单的离子化合物，可以交换化合价数字并写成下标，必要时约简。
6. Word Equations and State Symbols | 文字方程式与状态符号
and products. The general format is: reactant + reactant → product(s). The arrow (→) means 'reacts to form'.
文字方程式用反应物和生成物的名称描述化学反应。一般格式为：反应物 + 反应物 → 生成物。箭头（→）表示 “反应生成”。
water). Example: hydrochloric acid(aq) + sodium hydroxide(aq) → sodium chloride(aq) + water(l). State symbols must be included in balanced symbol equations but are useful even in word equations.
在每个物质后面写上状态符号以表示其物理状态：(s) 表示固体，(l) 表示液体，(g) 表示气体，(aq) 表示水溶液（溶于水）。例如：盐酸(aq) + 氢氧化钠(aq) → 氯化钠(aq) + 水(l)。状态符号应出现在配平符号方程式中，即使在文字方程式中也很有用。
s) + carbon dioxide(g); zinc(s) + hydrochloric acid(aq) → zinc chloride(aq) + hydrogen(g).
需要掌握的常见反应：镁(s) + 氧气(g) → 氧化镁(s)；碳酸钙(s) → 氧化钙(s) + 二氧化碳(g)；锌(s) + 盐酸(aq) → 氯化锌(aq) + 氢气(g)。
7. Relative Atomic Mass and Formula Mass | 相对原子质量与式量
The relative atomic mass (Aᵣ) of an element is the average mass of its atoms compared to 1/12th of the mass of a carbon-12 atom. It is a dimensionless number, roughly equal to the mass number of the most common isotope. You can find Aᵣ values on 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 相比较得到的数值。它是一个无量纲数，约等于最常见同位素的质量数。可以在周期表中找到 Aᵣ 值。
| Element | Symbol | Aᵣ |
|---|---|---|
| Hydrogen | H | 1 |
| Carbon | C | 12 |
| Oxygen | O | 16 |
| Sodium | Na | 23 |
| Calcium | Ca | 40 |
Mᵣ of CaCO₃ = 40 + 12 + (3 × 16) = 100. Formula mass is used to calculate reacting masses later in your chemistry studies.
化合物的式量（Mᵣ）是其化学式中所有原子的相对原子质量之和。例如，H₂O 的 Mᵣ = (2 × 1) + 16 = 18；CaCO₃ 的 Mᵣ = 40 + 12 + (3 × 16) = 100。式量将在后续化学学习中用于计算反应质量。
8. Density and Particle Arrangement | 密度与粒子排列
Density is a measure of how much mass is packed into a given volume. The formula is:
密度是衡量单位体积内含有多少质量的物理量。其计算公式为：
density = mass ÷ volume
密度 = 质量 ÷ 体积
m / V. The standard units are g/cm³ for solids and liquids, and g/dm³ or kg/m³ for gases.
通常密度用符号 ρ 表示，质量用 m，体积用 V：ρ = m / V。固、液体常用单位为 g/cm³，气体常用 g/dm³ 或 kg/m³。
In general, the particles in solids are most tightly packed, giving them the highest density; liquids are slightly less dense, while gases have very low densities because the particles are far apart. Water is a notable exception: ice (solid) is less dense than liquid water, which is why ice floats.
一般来说，固体中粒子堆积最紧密，因此密度最大；液体密度略低，气体因粒子间距很远而密度极低。水是一个明显的例外：冰（固体）的密度小于液态水，所以冰能浮在水面上。
9. Acids, Alkalis and the pH Scale | 酸、碱与 pH 值
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Alkalis are soluble bases that release hydroxide ions (OH⁻) in water; examples are sodium hydroxide (NaOH) and potassium hydroxide (KOH).
酸是在水中电离出氢离子（H⁺）的物质。实验室常见酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。碱是可溶的、在水中释放氢氧根离子（OH⁻）的物质；例如氢氧化钠（NaOH）和氢氧化钾（KOH）。
ne. Universal indicator turns red in strong acids, green in neutral and purple in strong alkalis.
pH 值用于衡量溶液的酸碱性，范围为 0 至 14：pH < 7 为酸性，pH = 7 为中性，pH > 7 为碱性。通用指示剂在强酸中呈红色，中性溶液中呈绿色，强碱中呈紫色。
salt + water. For example: hydrochloric acid + sodium hydroxide → sodium chloride + water.
中和反应是酸与碱之间的反应，生成盐和水：酸 + 碱 → 盐 + 水。例如：盐酸 + 氢氧化钠 → 氯化钠 + 水。
10. Conservation of Mass in Chemical Reactions | 化学反应中的质量守恒
The law of conservation of mass states that in a chemical reaction, the total mass of the reactants equals the total mass of the products. Atoms are neither created nor destroyed; they are simply rearranged to form new substances.
质量守恒定律表明，在化学反应中，反应物的总质量等于生成物的总质量。原子既不会被创造也不会被消灭，它们只是重新组合形成了新的物质。
ith oxygen: 2H₂ + O₂ → 2H₂O. If 4 g of hydrogen react with 32 g of oxygen, exactly 36 g of water are produced.
这意味着化学方程式必须配平，显示两边每种原子的数目相同。例如，氢气与氧气反应：2H₂ + O₂ → 2H₂O。若
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