📚 Year 8 CCEA Chemistry: Core Knowledge Review | Year 8 CCEA 化学：核心知识点梳理
This guide covers all the essential topics in Year 8 Chemistry for the CCEA curriculum, providing a clear review of key concepts from particles to reactions. Each section explains the idea in simple terms, with examples and comparisons to help you master the fundamentals.
本指南涵盖 CCEA 课程 Year 8 化学的所有核心主题，清晰梳理从粒子到反应的关键概念。每个部分用简单的语言解释概念，并配有示例和对比，帮助你掌握基础知识。
1. States of Matter | 物质的状态
All substances can exist as solids, liquids or gases. These are called the three states of matter. Each state has different properties because of how the particles are arranged and how they move.
所有物质都能以固体、液体或气体的形式存在，这些被称为物质的三态。每种状态的性质不同，取决于粒子的排列方式和运动情况。
In solids, particles are tightly packed in a regular pattern. They vibrate in fixed positions, which gives solids a definite shape and volume.
在固体中，粒子紧密排列成规则的图案。它们在固定的位置上振动，使固体有确定的形状和体积。
In liquids, particles are still close together but can slide past each other. This means a liquid has a fixed volume but takes the shape of its container.
在液体中，粒子彼此靠近但可以相互滑动。这意味着液体有固定的体积，但形状随容器而变。
In gases, particles are far apart and move rapidly in all directions. Gases have no definite shape or volume and are easily compressed.
在气体中，粒子相距很远，朝各个方向快速运动。气体没有固定的形状和体积，容易压缩。
2. The Particle Theory | 粒子理论
The particle theory (also called the kinetic theory) helps explain the behaviour of solids, liquids and gases. It states that all matter is made of tiny particles that are constantly moving.
粒子理论（也称为动理论）有助于解释固体、液体和气体的行为。它指出所有物质都由微小粒子组成，这些粒子在不停地运动。
The energy of the particles depends on temperature – the higher the temperature, the faster they move. This is why heating a substance can cause a change of state.
粒子的能量取决于温度——温度越高，运动越快。这就是加热物质会导致状态变化的原因。
In solids, strong forces hold particles close together; in liquids, the forces are weaker; in gases, the forces of attraction are very weak, so particles are free to spread out.
在固体中，粒子间作用力强，使它们紧密排列；在液体中，作用力较弱；在气体中，粒子间的吸引力非常弱，因此粒子可以自由扩散。
3. Melting, Freezing, Boiling and Condensation | 熔化、凝固、沸腾和冷凝
zing (liquid → solid), boiling / evaporating (liquid → gas) and condensing (gas → liquid).
状态的变化涉及增加能量（加热）或减少能量（冷却）。主要过程有：熔化（固体→液体）、凝固（液体→固体）、沸腾/蒸发（液体→气体）和冷凝（气体→液体）。
The temperature at which a solid melts is its melting point; the temperature at which a liquid boils is its boiling point. Pure substances have sharp, fixed melting and boiling points.
固体熔化时的温度称为熔点；液体沸腾时的温度称为沸点。纯物质有清晰、固定的熔点和沸点。
During a change of state, the temperature stays constant until the change is complete. The energy supplied goes into overcoming the forces between particles rather than raising the temperature.
在状态变化期间，温度保持不变，直到变化完成。提供的能量用于克服粒子间的相互作用力，而不是升高温度。
4. Diffusion in Gases and Liquids | 气体和液体中的扩散
Diffusion is the net movement of particles from a region of high concentration to a region of low concentration, until they are evenly spread out. It occurs because particles are always in random motion.
扩散是粒子从高浓度区域向低浓度区域的净运动，直到分布均匀。扩散发生的原因是粒子总在随机运动。
Diffusion is fastest in gases, slower in liquids, and does not happen in solids because the particles cannot move freely.
气体中扩散最快，液体中较慢，固体中不会发生扩散，因为粒子不能自由移动。
Increasing temperature speeds up diffusion, because particles gain kinetic energy and move faster.
升高温度会加快扩散，因为粒子获得动能，运动得更快。
Everyday examples include the smell of perfume spreading through a room, or a crystal of potassium permanganate dissolving and colouring water purple.
日常例子包括香水的香味在房间中扩散，或高锰酸钾晶体溶解使水变成紫色。
5. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance that consists of only one type of atom. Examples: oxygen (O₂), iron (Fe), gold (Au).
元素是由同一种原子组成的纯物质。例如：氧气 (O₂)、铁 (Fe)、金 (Au)。
A compound is a pure substance made of two or more different types of atoms chemically bonded together. Examples: water (H₂O), carbon dioxide (CO₂), sodium chloride (NaCl).
化合物是由两种或多种不同种类的原子通过化学键结合而成的纯物质。例如：水 (H₂O)、二氧化碳 (CO₂)、氯化钠 (NaCl)。
A mixture contains two or more substances that are not chemically combined. They can be separated by physical methods such as filtration or distillation. Air is a mixture of gases; sea water is a mixture of water and dissolved salts.
混合物包含两种或多种未通过化学键结合的物质。它们可以用物理方法分离，如过滤或蒸馏。空气是气体混合物；海水是水和溶解盐的混合物。
Compounds have properties different from their elements, whereas mixtures retain the properties of the individual substances.
化合物的性质与其组成元素不同，而混合物保留了各组分物质原有的性质。
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Composition | One type of atom | Two or more elements chemically combined | Two or more substances physically mixed |
| Separation | Cannot be broken down | Only by chemical reactions | By physical methods |
6. The Periodic Table | 元素周期表
The periodic table lists all the known elements in order of increasing atomic number. Rows are called periods and columns are called groups.
元素周期表按原子序数递增的顺序列出了所有已知元素。横行称为周期，纵列称为族。
Elements in the same group have similar chemical properties because they have the same number of electrons in their outermost shells.
同一族的元素具有相似的化学性质，因为它们最外层电子数相同。
Metals are found on the left and centre of the table; non-metals are on the right. A stepped zigzag line separates them.
金属位于表的左侧和中部；非金属在右侧。一条阶梯状的锯齿线将它们分开。
Common elements you should know include:
你需要知道的常见元素有：
| Symbol | English Name | 中文名称 |
|---|---|---|
| H | Hydrogen | 氢 |
| C | Carbon | 碳 |
| N | Nitrogen | 氮 |
| O | Oxygen | 氧 |
| Na | Sodium | 钠 |
| Mg | Magnesium | 镁 |
| Cl | Chlorine | 氯 |
| Fe | Iron | 铁 |
| Cu | Copper | 铜 |
| Zn | Zinc | 锌 |
7. Separation Techniques | 分离技术
Filtration is used to separate an insoluble solid from a liquid. A filter paper lets the liquid pass through but traps the solid particles.
过滤用于分离不溶性固体和液体。滤纸能让液体通过，但截留固体颗粒。
Evaporation removes a solvent (e.g., water) from a solution, leaving the dissolved solid behind. This method is used to obtain salt from seawater.
蒸发是从溶液中去除溶剂（如水），留下溶解的固体。这种方法用于从海水中获取盐。
Simple distillation separates a pure solvent from a solution. The liquid is boiled, and the vapour is condensed back into a liquid in a different container. It can be used to obtain pure water from salt water.
简单蒸馏从溶液中分离出纯溶剂。液体被加热沸腾，蒸汽在另一个容器中冷凝回液体。可用于从盐水获得纯水。
Chromatography separates mixtures of dissolved substances, such as the dyes in inks or food colourings. Different substances move at different speeds
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