📚 KS3 Chemistry: 12 Key Topics Review | KS3 化学：12 大核心专题复习
Welcome to this complete KS3 Chemistry review. This guide brings together the twelve most important core topics you need to master before advancing to GCSE. Each section pairs a clear English explanation with a matching Chinese translation, so you can build confidence in both languages while revising.
欢迎阅读这份完整的 KS3 化学复习指南。本指南汇集了你在进入 GCSE 阶段之前需要掌握的 12 个核心专题。每个专题都配有清晰的英文讲解与对应的中文翻译，让你在复习过程中同时提升双语信心。
1. States of Matter | 物质的状态
Matter exists in three main states: solid, liquid and gas. The state of a substance depends on the balance between the forces holding its particles together and the kinetic energy of those particles. Heating or cooling changes this balance and causes changes of state.
物质主要有三种状态：固态、液态和气态。物质处于哪种状态，取决于微粒间相互吸引的作用力与微粒自身动能之间的平衡。加热或冷却会打破这种平衡，从而引起状态变化。
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Solids have a fixed shape and a fixed volume. Their particles vibrate around fixed positions and cannot move freely.
固体具有固定的形状和体积。其微粒在固定位置附近振动，不能自由移动。
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Liquids have a fixed volume but no fixed shape. Their particles are close together but can slide past one another.
液体具有固定的体积但没有固定的形状。其微粒排列紧密，但可以相互滑动。
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Gases have neither a fixed shape nor a fixed volume. Their particles are far apart and move rapidly in all directions.
气体既没有固定的形状，也没有固定的体积。其微粒彼此相距很远，并向各个方向快速运动。
Melting, freezing, boiling and condensing are all physical changes. For example, when ice melts at 0 °C, the particles gain energy and break free from their fixed positions, but the substance remains the same material — water.
熔化、凝固、沸腾和凝结都是物理变化。例如，当冰在 0 °C 熔化时，微粒获得能量并脱离固定位置，但物质本身仍然是同一种材料——水。
2. The Particle Model | 微粒模型
The particle model is a simple way of explaining how materials behave. It assumes that all matter is made of tiny, moving particles. The model can explain observable phenomena such as diffusion, pressure and changes of state.
微粒模型是一种解释物质行为方式的简便工具。它假设所有物质都由微小且运动的微粒组成。该模型能够解释扩散、压强和状态变化等可观察的现象。
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Diffusion is the spreading of particles from an area of high concentration to an area of low concentration. It happens fastest in gases because their particles move quickly and freely.
扩散是指微粒从高浓度区域向低浓度区域蔓延的过程。气体中扩散最快，因为气体微粒运动迅速且自由。
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Diffusion also occurs in liquids, but more slowly. A familiar example is the spreading of purple colour from a potassium manganate(VII) crystal placed in water.
液体中也会发生扩散，但速度较慢。一个常见的例子是高锰酸钾晶体放入水中后紫色逐渐扩散开来。
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Heating increases the energy of particles, making them move faster. This is why diffusion is quicker at higher temperatures.
加热会增加微粒的能量，使其运动加快。这就是为什么温度越高，扩散越快。
rate of diffusion ∝ temperature ↑, particle mass ↓
Remember that diffusion does not happen in solids, because their particles cannot move from place to place.
请记住，扩散不会在固体中发生，因为固体微粒无法从一个位置移动到另一个位置。
3. Atoms, Elements and Compounds | 原子、元素与化合物
An atom is the smallest particle of an element that can take part in a chemical reaction. An element contains only one type of atom. A compound contains two or more different types of atom that are chemically bonded together in fixed proportions.
原子是元素中能够参与化学反应的最小微粒。元素只含有一种类型的原子。化合物则含有两种或多种不同类的原子，它们以固定的比例通过化学键结合在一起。
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Elements are represented by chemical symbols, such as O for oxygen, Fe for iron and Na for sodium.
元素用化学符号表示，例如 O 代表氧，Fe 代表铁，Na 代表钠。
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Compounds have completely different properties from the elements that make them. For example, sodium is a reactive metal and chlorine is a toxic green gas, but sodium chloride is a safe white solid we use as table salt.
化合物的性质与其组成元素的性质完全不同。例如，钠是活泼金属，氯是有毒的黄绿色气体，但氯化钠却是我们用作食盐的安全白色固体。
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A chemical formula shows which atoms are in a compound. In H₂O, two hydrogen atoms are bonded to one oxygen atom.
化学式表示化合物中含有哪些原子。在 H₂O 中，两个氢原子与一个氧原子成键。
| Substance | Type | Atoms present |
| O₂ | Element | Oxygen only |
| CO₂ | Compound | Carbon + oxygen |
| NaCl | Compound | Sodium + chlorine |
4. Mixtures and Separation Techniques | 混合物与分离方法
A mixture contains two or more substances that are not chemically joined. The substances in a mixture keep their own properties, and they can usually be separated by physical methods. Choosing the right technique depends on the properties of the substances involved.
混合物含有两种或多种没有发生化学结合的物质。混合物中的各物质保留自身性质，通常可以用物理方法进行分离。选择合适的分离技术取决于所涉及物质的性质。
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Filtration separates an insoluble solid from a liquid. For example, sand can be removed from water using filter paper.
过滤用于分离不溶性固体与液体。例如，可以用滤纸将沙子从水中除去。
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Evaporation removes a liquid from a dissolved solid to leave the solid behind. For example, heating salt water leaves salt crystals.
蒸发是从溶液中除去液体并留下固体溶质的方法。例如，加热盐水可以得到食盐晶体。
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Distillation separates a solvent from a solution by boiling and condensing. Simple distillation can obtain pure water from seawater.
蒸馏通过沸腾和冷凝将溶剂从溶液中分离出来。简单蒸馏可以从海水中获得纯水。
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Chromatography separates different dissolved substances in a mixture, such as the different dyes in ink.
色谱法用于分离混合物中的不同可溶物质，例如墨水中的不同染料。
| Method | Separates | Key idea |
| Filtration | Insoluble solid + liquid | Particles too large to pass through filter paper |
| Evaporation | Dissolved solid + liquid | Liquid turns to vapour and escapes |
| Distillation | Solvent + dissolved solid | Solvent is boiled off and condensed |
| Chromatography | Different dissolved dyes | Substances move at different speeds on paper |
5. Physical and Chemical Changes | 物理变化与化学变化
A physical change is reversible and does not produce a new substance. A chemical change produces one or more new substances and is difficult to reverse. Being able to tell the difference is a key skill in chemistry.
物理变化是可逆的，并且不会产生新物质。化学变化会产生一种或多种新物质，且难以逆转。能够区分二者是化学学习中的关键技能。
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Physical changes include melting, freezing, evaporating and dissolving. The particles stay the same — only their arrangement or spacing changes.
物理变化包括熔化、凝固、蒸发和溶解。微粒本身保持不变，改变的只是它们的排列方式或间距。
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Chemical changes include burning, rusting, cooking and acid–carbonate reactions. New substances with new properties are formed.
化学变化包括燃烧、生锈、烹饪以及酸与碳酸盐的反应。反应后会生成具有新性质的新物质。
The five classic signs that a chemical reaction may have occurred are: a gas is released, a colour change appears, a precipitate forms, heat or light is given out, or the change is difficult to reverse.
判断是否发生化学反应的五个典型标志是：产生气体、出现颜色变化、形成沉淀、释放热或光，以及该变化难以逆转。
physical change: particles unchanged | chemical change: new substances formed
6. Acids and Alkalis | 酸与碱
An acid is a substance with a pH below 7, while an alkali is a soluble base with a pH above 7. The pH scale runs from 0 to 14 and tells us how acidic or alkaline a solution is. Indicators are dyes that change colour in acids and alkalis.
酸是 pH 值低于 7 的物质，而碱是可溶性的碱性物质，pH 值高于 7。pH 标度从 0 到 14，用来表示溶液的酸性或碱性程度。指示剂是在酸和碱中会变色的染料。
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Litmus paper turns red in acid and blue in alkali. Universal indicator gives a full range of colours across the pH scale.
石蕊试纸遇酸变红，遇碱变蓝。万能指示剂在整個 pH 范围内会显示一系列颜色。
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A strong acid such as hydrochloric acid (HCl) has a pH of 1; a weak acid such as vinegar has a pH of about 4.
像盐酸（HCl）这样的强酸 pH 为 1；而像食醋这样的弱酸 pH 约为 4。
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Acids taste sour, can corrode some metals, and turn blue litmus red. Alkalis feel soapy and turn red litmus blue.
酸有酸味，能腐蚀某些金属，并使蓝色石蕊变红。碱有滑腻感，能使红色石蕊变蓝。
0 — 3 strong acid | 4 — 6 weak acid | 7 neutral | 8 — 10 weak alkali | 11 — 14 strong alkali
Pure water is neutral with a pH of exactly 7.
纯水呈中性，pH 值正好为 7。
7. Neutralisation | 中和反应
Neutralisation is the reaction between an acid and a base (or alkali) to form a salt and water. Since the acid provides H⁺ ions and the alkali provides OH⁻ ions, the reaction removes both and produces neutral water.
中和反应是酸与碱（或碱溶液）之间发生的反应，生成盐和水。由于酸提供 H⁺ 离子，碱提供 OH⁻ 离子，反应会将二者同时消耗掉，并生成中性的水。
acid + base → salt + water
For example, hydrochloric acid reacts with sodium hydroxide to give sodium chloride and water.
例如，盐酸与氢氧化钠反应生成氯化钠和水。
hydrochloric acid + sodium hydroxide → sodium chloride + water
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Neutralisation has many everyday uses. Indigestion tablets contain bases such as magnesium hydroxide to neutralise excess stomach acid.
中和反应在日常生活中应用很广。治疗消化不良的药片含有氢氧化镁等碱，可用来中和胃中过多的酸。
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Farmers add lime (calcium oxide or calcium hydroxide) to acidic soil to improve crop growth.
农民会向酸性土壤中添加石灰（氧化钙或氢氧化钙），以改善作物生长。
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Bee stings are acidic and can be treated with a weak alkali; wasp stings are alkaline and can be treated with a weak acid such as vinegar.
蜜蜂蜇伤处呈酸性，可用弱碱处理；黄蜂蜇伤处呈碱性，可用醋等弱酸处理。
8. Metals and Non-metals | 金属与非金属
Elements can be divided into metals and non-metals. On the periodic table, metals appear on the left and in the middle, while non-metals appear on the right. The dividing line is a zig-zag ‘staircase’ that separates the two groups.
元素可以分为金属和非金属。在元素周期表中，金属位于左侧和中部，非金属位于右侧。二者之间有一条锯齿形的“阶梯线”作为分界。
| Property | Metals | Non-metals |
| Appearance | Shiny | Dull |
| Conduction | Good conductors of heat and electricity | Poor conductors (except graphite) |
| Malleability | Malleable and ductile | Brittle when solid |
| State at room temperature | Usually solid (mercury is the exception) | Solid, liquid or gas |
Most metals also have high melting points and high densities. Non-metals such as sulfur and carbon are often dull and brittle. Oxygen, nitrogen and chlorine are gaseous non-metals at room temperature.
大多数金属还具有高熔点和较高的密度。硫和碳等非金属通常无光泽且易碎。氧、氮和氯在室温下是气态非金属。
9. The Reactivity Series | 金属活动性顺序
The reactivity series is a list of metals in order of how readily they react with water, dilute acid and oxygen. A more reactive metal will displace a less reactive metal from its compound. This rule is the basis of many extraction and competition reactions.
金属活动性顺序是将金属按照它们与氧气、水和稀酸反应的难易程度排列而成的序列。较活泼的金属能够将较不活泼的金属从其化合物中置换出来。这一规律是许多提炼反应和竞争反应的基础。
potassium > sodium > calcium > magnesium > aluminium > zinc > iron > copper > gold
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Potassium, sodium and calcium react vigorously with cold water, producing hydrogen gas and a hydroxide.
钾、钠和钙与冷水剧烈反应，产生氢气和相应的氢氧化物。
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Magnesium, zinc and iron react steadily with dilute hydrochloric acid to produce hydrogen; copper and gold do not react.
镁、锌和铁能与稀盐酸平稳反应并产生氢气；铜和金则不与稀盐酸反应。
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If iron is placed in copper sulfate solution, a displacement reaction occurs: iron coats itself with brown copper while iron sulfate forms in the solution.
如果将铁放入硫酸铜溶液中，会发生置换反应：铁的表面会覆盖一层棕色的铜，同时溶液中生成硫酸亚铁。
iron + copper sulfate → iron sulfate + copper
The reactivity series also explains why metals such as gold are found uncombined in the Earth while reactive metals like aluminium must be extracted from their ores using electrolysis.
金属活动性顺序还可以解释：为什么金等金属在自然界中以游离态存在，而铝等活泼金属必须通过电解法从矿石中提取。
10. The Periodic Table | 元素周期表
The periodic table arranges all known elements in order of increasing atomic number. Elements in the same vertical column, called a group, have similar chemical properties because they have the same number of outer electrons. Horizontal rows are called periods.
元素周期表按照原子序数递增的顺序排列所有已知元素。同一纵列（称为“族”）中的元素具有相似的化学性质，因为它们的最外层电子数相同。横排称为“周期”。
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Group 1 elements (lithium, sodium, potassium) are soft, reactive metals that react with water to produce hydrogen. Their reactivity increases going down the group.
第 1 族元素（锂、钠、钾）是柔软且活泼的金属，能与水反应产生氢气。从上到下，它们的活泼性逐渐增强。
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Group 7 elements (fluorine, chlorine, bromine, iodine) are non-metals with coloured vapours. Their reactivity decreases going down the group.
第 7 族元素（氟、氯、溴、碘）是具有有色蒸气的非金属。从上到下，它们的活泼性逐渐减弱。
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Group 0 elements (helium, neon, argon) are called the noble gases. They are very unreactive because their outer electron shells are full.
第 0 族元素（氦、氖、氩）被称为稀有气体。由于它们的最外层电子排布已满，因此非常不活泼。
Knowing the group number helps you predict how an element will behave. For example, all Group 1 metals form 1+ ions and all Group 7 non-metals form 1− ions.
了解族序数有助于预测元素的行为。例如，所有第 1 族金属都形成 1+ 离子，而所有第 7 族非金属都形成 1− 离子。
11. The Earth and Atmosphere | 地球与大气
The Earth has a layered structure: the crust, the mantle and the core. The crust and the top of the mantle form the rigid lithosphere. The atmosphere surrounding the planet is a mixture of gases that has supported life for billions of years.
地球具有分层结构：地壳、地幔和地核。地壳与地幔顶部共同构成坚硬的岩石圈。环绕地球的大气层是一种气体混合物，数十亿年来一直维持着生命活动。
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Today’s air is approximately 78% nitrogen, 21% oxygen and about 1% other gases including argon and carbon dioxide.
当今的空气大约含 78% 的氮气、21% 的氧气，以及约 1% 的其他气体，包括氩气和二氧化碳。
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The greenhouse effect is a natural process in which gases such as CO₂ and methane trap heat in the atmosphere. Without it, Earth would be too cold to support most life.
温室效应是一个自然过程：二氧化碳和甲烷等气体将热量截留在大气中。如果没有它，地球将会过于寒冷，无法维持大多数生命。
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Human activities such as burning fossil fuels increase greenhouse gas levels, which strengthens the greenhouse effect and leads to global warming and climate change.
燃烧化石燃料等人类活动会增加温室气体含量，从而增强温室效应，并导致全球变暖和气候变化。
The carbon cycle describes how carbon moves continuously between the atmosphere, living organisms, oceans and rocks through processes such as photosynthesis, respiration and combustion.
碳循环描述了碳如何通过光合作用、呼吸作用和燃烧等过程，在大气、生物体、海洋和岩石之间持续流动。
12. Energy Changes in Reactions | 反应中的能量变化
All chemical reactions involve energy changes. When bonds are broken, energy is taken in; when bonds are made, energy is released. The overall energy change of a reaction tells us whether it is exothermic or endothermic.
所有化学反应都伴随能量变化。断开化学键时需要吸收能量，形成化学键时会释放能量。一个反应的总体能量变化决定了它是放热反应还是吸热反应。
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Exothermic reactions release energy to the surroundings, usually as heat or light. Burning, neutralisation and respiration are examples. The temperature of the surroundings increases.
放热反应向周围环境释放能量，通常以热或光的形式。燃烧、中和反应和呼吸作用都是例子。反应后周围温度升高。
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Endothermic reactions take in energy from the surroundings. Photosynthesis and thermal decomposition are examples. The temperature of the surroundings decreases.
吸热反应从周围环境吸收能量。光合作用和热分解就是例子。反应后周围温度降低。
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Self-heating cans and hand warmers rely on exothermic reactions, while sports injury cold packs often use an endothermic reaction between ammonium nitrate and water.
自热罐和暖手宝利用的是放热反应，而运动损伤用的冰敷袋通常利用硝酸铵与水的吸热反应。
exothermic
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