📚 Year 7 Edexcel Chemistry Quick Formula & Theorem Reference Handbook | 7年级爱德思化学：公式定理速查手册
This handbook presents key formulas, rules, and core principles you need to master in Year 7 Edexcel Chemistry. Use it as a quick revision tool before tests, when solving problems, or while writing up experiments. Each section explains a concept first in English, then in Chinese, to help you build subject vocabulary in both languages and deepen your scientific understanding.
本手册整理了7年级爱德思化学中必须掌握的关键公式、规则与核心原理，可作为考试前、解题时或撰写实验报告时的快速复习工具。每个部分先用英文解释概念，再用中文复述，帮助你建立中英双语学科词汇，加深对科学的理解。
1. Law of Conservation of Mass | 质量守恒定律
In any chemical reaction, the total mass of the reactants always equals the total mass of the products. Atoms are rearranged, but none are created or destroyed. This is why chemical equations must be balanced.
在任何化学反应中，反应物的总质量总是等于生成物的总质量。原子只是重新排列，没有被创造或消失。这就是化学方程式必须配平的原因。
When magnesium ribbon burns in air, the mass of the white ash (magnesium oxide) appears greater than the original metal, but that is because oxygen from the air has combined with magnesium. If you weigh the container with the trapped gas, the total mass stays the same.
当镁条在空气中燃烧时，生成的白色粉末（氧化镁）的质量看起来比原来的金属大，但这是因为空气中的氧气与镁结合了。如果将容器连同封闭的气体一起称量，总质量仍然不变。
mass of reactants = mass of products
反应物的质量 = 生成物的质量
2. Atoms, Elements and Compounds – Key Definitions | 原子、元素与化合物的关键定义
An atom is the smallest particle of an element that can take part in a chemical reaction. Each element consists of only one type of atom and is represented by a chemical symbol, such as H for hydrogen, O for oxygen, Fe for iron.
原子是能参与化学反应的元素最小微粒。每种元素只由一种原子组成，并用一个化学符号表示，例如氢用 H、氧用 O、铁用 Fe。
A compound is a substance made of two or more different elements chemically joined in fixed proportions. The properties of a compound are entirely different from the elements it contains. For instance, sodium chloride (NaCl) is a white crystalline solid safe to eat, whereas sodium is a soft, highly reactive metal and chlorine is a poisonous green gas.
化合物是由两种或两种以上不同元素按固定比例结合而成的物质。化合物的性质与它所含的元素完全不同。例如，氯化钠（NaCl）是可食用的白色晶体，而钠是一种柔软、反应剧烈的金属，氯则是有毒的黄绿色气体。
A mixture contains two or more substances that are not chemically combined and can be separated by physical methods such as filtration or distillation.
混合物含有两种或以上未发生化学结合的物质，可以通过过滤、蒸馏等物理方法进行分离。
3. Chemical Formula Writing Rules | 化学式的书写规则
A chemical formula uses symbols and subscript numbers to show the types and numbers of atoms in a compound. The metal (or the less electronegative element) is usually written first. For covalent compounds of two non‑metals, the element closer to the left of the periodic table often comes first (e.g., CO₂, not O₂C).
化学式用符号和下标数字表示化合物中原子的种类和数量。通常金属（或电负性较弱的元素）写在前面。对于两种非金属组成的共价化合物，周期表中靠左的元素通常写在前面（如 CO₂，而不是 O₂C）。
The subscript number is written immediately after the element symbol and tells you how many atoms of that element are present. If there is only one atom, no number is written. Never change the formula to balance an equation; you only adjust the large number in front (the coefficient).
下标数字紧跟在元素符号之后，表示该原子的数目。如果只有1个原子，则不写数字。千万不要通过改变化学式来配平方程式，只能调整化学式前面的系数（化学计量数）。
Example: H₂O means 2 hydrogen atoms and 1 oxygen atom
示例：H₂O 表示 2 个氢原子和 1 个氧原子
4. Balancing Chemical Equations | 配平化学方程式
A balanced chemical equation shows the correct ratio of reactants and products so that the number of atoms of each element is the same on both sides. Follow this step‑by‑step method: first write the word equation, then the correct chemical formulae, and finally add coefficients to balance the atoms.
配平的化学方程式显示了反应物与生成物的正确比例，使每种元素的原子数目在两边相等。按步骤来：先写出文字表达式，再写出正确的化学式，最后添加系数来平衡原子。
Start with the most complex molecule. Balance metallic elements, then non‑metals, then hydrogen, and leave oxygen for last. Finally, check that all coefficients are in the simplest whole‑number ratio.
从最复杂的分子开始。先平衡金属元素，再平衡非金属元素、氢元素，最后平衡氧元素。最后检查所有系数是否为最简整数比。
Unbalanced: H₂ + O₂ → H₂O
Balanced: 2H₂ + O₂ → 2H₂O
未配平：H₂ + O₂ → H₂O
已配平：2H₂ + O₂ → 2H₂O
5. Relative Atomic Mass and Formula Mass | 相对原子质量与式量
The 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. You find Aᵣ values on the periodic table. The relative formula mass (Mᵣ) of a compound is the sum of the Aᵣ values of all the atoms in its formula.
相对原子质量（Aᵣ）是元素原子的平均质量与碳‑12原子质量的1/12的比值，没有单位。在周期表上可以找到 Aᵣ 值。化合物的相对式量（Mᵣ）是其化学式中所有原子的 Aᵣ 值之和。
For example, to find the Mᵣ of water (H₂O): Aᵣ of H = 1, Aᵣ of O = 16, so Mᵣ = (2×1) + 16 = 18. For calcium carbonate (CaCO₃): Ca=40, C=12, O=16×3, total = 100. This number is useful for calculating amounts in reactions later in KS3 and KS4.
例如，计算水（H₂O）的 Mᵣ：H 的 Aᵣ=1，O 的 Aᵣ=16，Mᵣ = (2×1)+16 = 18。碳酸钙（CaCO₃）：Ca=40, C=12, O=16×3，总和=100。这个数值在 KS3 和 KS4 阶段计算反应量时很有用。
Mᵣ = Σ (number of atoms × Aᵣ of the element)
式量 = Σ（原子个数 × 该元素的相对原子质量）
6. State Symbols and Their Meaning | 状态符号及其含义
In chemical equations, state symbols show the physical state of each substance. The four symbols are: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution (the substance dissolved in water). Using the correct state symbol is important because state changes affect energy changes and reaction rates.
在化学方程式中，状态符号表示每种物质的物理状态。共有四种符号：(s) 表示固体，(l) 表示液体，(g) 表示气体，(aq) 表示水溶液（物质溶于水中）。使用正确的状态符号很重要，因为状态变化会影响能量变化和反应速率。
For example, the reaction between hydrochloric acid and limestone can be written as: CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g). Notice that limestone is a solid, the acid and calcium chloride are aqueous, water is liquid, and carbon dioxide is a gas evolved.
例如，盐酸与石灰石的反应可写为：CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)。注意石灰石是固体，酸和氯化钙是水溶液，水是液体，二氧化碳是逸出的气体。
7. Ions and Common Ionic Charges | 离子与常见离子电荷
When atoms gain or lose electrons, they become ions. Metals tend to lose electrons to form positive ions (cations), while non‑metals tend to gain electrons to form negative ions (anions). The charge on an ion is written as a superscript after the symbol, e.g., Na⁺, Cl⁻, Mg²⁺, O²⁻.
当原子获得或失去电子时，就变成了离子。金属倾向于失去电子形成阳离子（正离子），而非金属倾向于获得电子形成阴离子（负离子）。离子电荷写在元素符号的右上角，如 Na⁺、Cl⁻、Mg²⁺、O²⁻。
For Group 1 elements, the ion charge is always 1⁺; Group 2 is 2⁺; Group 7 (halogens) is 1⁻; Group 6 is 2⁻. Many transition metals can form more than one ion, but Year 7 you mainly meet iron Fe²⁺ and Fe³⁺. Polyatomic ions contain more than one atom: hydroxide OH⁻, sulfate SO₄²⁻, nitrate NO₃⁻, carbonate CO₃²⁻, ammonium NH₄⁺.
第1族元素的离子电荷总是 1⁺；第2族是 2⁺；第7族（卤素）是 1⁻；第6族是 2⁻。许多过渡金属能形成不止一种离子，但7年级主要接触铁离子 Fe²⁺ 和 Fe³⁺。多原子离子含有多个原子：氢氧根 OH⁻、硫酸根 SO₄²⁻、硝酸根 NO₃⁻、碳酸根 CO₃²⁻、铵根 NH₄⁺。
8. Naming Compounds from Their Ions | 从离子命名化合物
A compound formed from a metal and a non‑metal is named by writing the metal first, then the non‑metal with the ending changed to ‘‑ide’. For example, sodium and chlorine form sodium chloride; magnesium and oxygen form magnesium oxide. If two non‑metals combine, the one with the lower group number (or the one closer to the left) is named first, and prefixes such as ‘mono‑’, ‘di‑’, ‘tri‑’ are often used: carbon dioxide (CO₂), sulfur trioxide (SO₃).
由金属和非金属形成的化合物命名时，先写金属名称，再将非金属词尾改为“‑ide”。例如，钠和氯形成氯化钠（sodium chloride）；镁和氧形成氧化镁（magnesium oxide）。如果两种非金属结合，族序数较低（或更靠左）的元素先命名，并常使用前缀如“单 ‑”、“二 ‑”、“三 ‑”：二氧化碳（CO₂）、三氧化硫（SO₃）。
Compounds containing a polyatomic ion like sulfate or carbonate keep their ion name: calcium sulfate (CaSO₄), sodium carbonate (Na₂CO₃). When a metal can form more than one ion, Roman numerals show the charge: iron(II) chloride for FeCl₂ and iron(III) chloride for FeCl₃.
含有硫酸根或碳酸根等多原子离子的化合物保留离子名称：硫酸钙（CaSO₄）、碳酸钠（Na₂CO₃）。当一种金属能形成多种离子时，用罗马数字表示电荷：氯化亚铁（FeCl₂）和氯化铁（FeCl₃）。
9. The pH Scale and Neutralisation | pH 值与中和反应
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 (strong acid) to 14 (strong alkali). A pH of 7 is neutral – pure water is the standard. Acids contain H⁺ ions in solution; alkalis contain OH⁻ ions in solution. Universal indicator changes colour through red, orange, yellow, green, blue, violet as pH increases.
pH 值范围用于衡量溶液的酸碱度，从 0（强酸）到 14（强碱）。pH 7 为中性——纯净水是标准。酸在水溶液中含有 H⁺ 离子，碱在水溶液中含有 OH⁻ 离子。通用指示剂随着 pH 升高会依次呈现红、橙、黄、绿、蓝、紫色。
Neutralisation is a reaction between an acid and a base (or alkali) that produces a salt and water. The general word equation is:
中和反应是酸与碱（或碱溶液）反应生成盐和水的反应。通用文字表达式为：
acid + base → salt + water
酸 + 碱 → 盐 + 水
For example, hydrochloric acid + sodium hydroxide → sodium chloride + water. If an alkali reacts with an acid, the ionic equation H⁺ + OH⁻ → H₂O shows the essential process taking place.
例如，盐酸 + 氢氧化钠 → 氯化钠 + 水。如果是碱溶液与酸反应，离子方程式 H⁺ + OH⁻ → H₂O 体现了发生的核心过程。
10. Common Types of Chemical Reaction | 常见化学反应类型
In combustion, a fuel (often a hydrocarbon) reacts with oxygen to release energy, produce carbon dioxide and water. Complete combustion word equation: fuel + oxygen → carbon dioxide + water. Incomplete combustion can produce carbon monoxide (CO) and soot (C).
在燃烧反应中，燃料（通常是碳氢化合物）与氧气反应，释放能量，生成二氧化碳和水。完全燃烧的文字表达式：燃料 + 氧气 → 二氧化碳 + 水。不完全燃烧可能产生一氧化碳（CO）和碳烟（C）。
In a displacement reaction, a more reactive metal pushes a less reactive metal out of its compound. For example: magnesium + copper sulfate → magnesium sulfate + copper. The reactivity series helps predict whether displacement will happen: potassium, sodium, lithium, calcium, magnesium, aluminium, zinc, iron, tin, lead, (hydrogen), copper, silver, gold.
在置换反应中，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。例如：镁 + 硫酸铜 → 硫酸镁 + 铜。活动性顺序有助于预测置换能否发生：钾、钠、锂、钙、镁、铝、锌、铁、锡、铅、（氢）、铜、银、金。
Thermal decomposition breaks down a compound into simpler substances using heat. Metal carbonates decompose to metal oxide and carbon dioxide: copper carbonate → copper oxide + carbon dioxide (green solid → black solid + CO₂ gas).
热分解是利用加热将化合物分解成更简单的物质。金属碳酸盐分解为金属氧化物和二氧化碳：碳酸铜 → 氧化铜 + 二氧化碳（绿色固体 → 黑色固体 + CO₂ 气体）。
11. Separation Techniques and Key Principles | 分离方法与关键原理
Filtration separates an insoluble solid from a liquid. The mixture is poured through filter paper; the solid (residue) stays in the paper, the liquid (filtrate) passes through. Evaporation is used to obtain a soluble solid from a solution by heating until all the water evaporates, leaving the solid behind. Crystallisation is gentler – it gives well‑formed crystals by letting the solution cool slowly.
过滤用于分离不溶性固体与液体。混合物通过滤纸，固体（残渣）留在纸上，液体（滤液）通过。蒸发通过加热使溶液中的水全部蒸发，留下可溶性固体。结晶法更温和——通过让溶液缓慢冷却得到形状规则的晶体。
Distillation separates a solvent from a solution by boiling and condensing. Simple distillation can collect pure water from salt water. Chromatography separates mixtures of dissolved substances, e.g. dyes in ink, based on their different solubilities. A substance with identical Rf value to a known sample under the same conditions is likely the same chemical.
蒸馏通过沸腾和冷凝分离溶液中的溶剂。简单蒸馏能从盐水中收集纯水。色谱法根据溶解物质的不同溶解度分离混合物，如墨水中染料。在相同条件下，Rf 值与已知样品相同的物质很可能是同一种化学物质。
Rf = distance travelled by substance / distance travelled by solvent front
Rf = 物质移动距离 / 溶剂前沿移动距离
12. Key Formulae to Memorise – Air Composition and Water Treatment | 必记的公式与数据——空气组成与水处理
Year 7 students need to recall the approximate composition of air: about 78 % nitrogen (N₂), 21 % oxygen (O₂), 0.9 % argon (Ar), 0.04 % carbon dioxide (CO₂), and variable amounts of water vapour. The atmosphere also contains noble gases in very small amounts.
7年级学生需要记住空气的大致组成：约 78% 氮气（N₂）、21% 氧气（O₂）、0.9% 氩气（Ar）、0.04% 二氧化碳（CO₂），以及可变含量的水蒸气。大气中还含有极少量的稀有气体。
For water purification, the main stages are sedimentation, filtration, and chlorination. Chlorine kills harmful microorganisms. In some areas, fluoride is added to reduce tooth decay. Hard water contains dissolved calcium and magnesium ions; it forms scum with soap, but it can be softened by boiling (for temporary hardness) or by adding washing soda.
水净化主要经历沉降、过滤和氯化消毒。氯能杀灭有害微生物。在一些地区会添加氟化物以减少龋齿。硬水含有溶解的钙离子和镁离子，与肥皂形成浮渣，但可通过煮沸（暂时硬水）或加入洗涤碱软化。
These figures and simple methods are frequently tested in the Edexcel Year 7 Chemistry examination, so commit them to memory.
这些数据和简单方法在爱德思7年级化学考试中经常出现，请牢记。
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