📚 Core Knowledge Review for Year 7 CAIE Chemistry | Year 7 CAIE 化学：核心知识点梳理
Entering Year 7 Chemistry under the CAIE framework, students begin to explore the fundamental ideas that explain the material world. This article presents a structured review of the core topics, including the particle model, states of matter, elements and compounds, simple atomic structure, chemical reactions, acids and alkalis, air composition, and separation methods. By mastering these concepts, learners build a solid foundation for future studies in IGCSE Chemistry.
在 CAIE 体系下进入七年级化学学习，学生开始探索解释物质世界的基本概念。本文系统梳理核心主题，包括粒子模型、物态、元素与化合物、简单原子结构、化学反应、酸和碱、空气成分以及分离方法。掌握这些概念将为未来的 IGCSE 化学学习奠定坚实基础。
1. The Particle Model of Matter | 物质的粒子模型
All matter is made up of tiny particles that are constantly moving. In solids, the particles are packed closely in a fixed arrangement and can only vibrate in place. This explains why solids have a definite shape and volume.
所有物质均由不断运动的微小粒子构成。在固体中，粒子紧密排列在固定位置上，只能就地振动。这解释了为什么固体具有固定的形状和体积。
In liquids, the particles are still close together but can slide past each other. They take the shape of the container but keep a constant volume. In gases, the particles are far apart and move rapidly in all directions, so gases have no fixed shape or volume and can be compressed easily.
在液体中，粒子仍然紧密接触，但可以相互滑动。液体呈现容器的形状并保持固定的体积。在气体中，粒子间距很大，朝各个方向快速运动，因此气体没有固定的形状和体积，且容易被压缩。
2. States of Matter and Changes of State | 物态变化
The three common states of matter are solid, liquid and gas. A change of state happens when energy is added or removed. Melting (solid to liquid) and boiling/evaporating (liquid to gas) require heat energy. Freezing (liquid to solid) and condensation (gas to liquid) release heat energy.
常见的物质三种状态为固态、液态和气态。当能量增加或减少时，物质会发生状态变化。熔化（固→液）和沸腾/蒸发（液→气）需要吸收热量。凝固（液→固）和冷凝（气→液）会释放热量。
During a change of state, the temperature of the substance stays constant even though heat is being added or removed. The energy is used to overcome or form the forces between particles rather than to raise the temperature. Sublimation is a special change where a solid turns directly into a gas, like solid carbon dioxide (dry ice).
在物态变化过程中，尽管有热量的吸收或释放，物质的温度却保持不变。这些能量被用来克服或形成粒子间的作用力，而不是升高温度。升华是一种特殊变化，固体直接变为气体，例如固态二氧化碳（干冰）。
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. Examples include oxygen (O), iron (Fe) and gold (Au). Elements cannot be broken down into simpler substances by chemical means. They are listed in the Periodic Table.
元素是由同一种原子组成的纯净物，例如氧（O）、铁（Fe）和金（Au）。元素不能通过化学方法分解成更简单的物质。它们列在元素周期表中。
A compound is a pure substance formed when two or more elements chemically combine in a fixed proportion. Water (H₂O) always contains hydrogen and oxygen in a 2:1 ratio. The properties of a compound are very different from the properties of its constituent elements. A mixture contains two or more substances (elements or compounds) that are not chemically joined and can be separated by physical methods. Air is a mixture of gases, and its composition can vary slightly.
化合物是由两种或两种以上元素按固定比例化合而成的纯净物。水（H₂O）中氢和氧的比例始终为 2:1。化合物的性质与其组成元素的性质大不相同。混合物含有两种或多种未通过化学键结合的物质（元素或化合物），并可通过物理方法分离。空气是一种气体混合物，其成分可略有变化。
4. Atoms and Molecules | 原子与分子
An atom is the smallest particle of an element that can take part in a chemical reaction. Each atom contains a tiny central nucleus made up of protons and neutrons, surrounded by electrons moving around the nucleus. The number of protons determines which element the atom belongs to.
原子是能参与化学反应的元素最小粒子。每个原子含有一个由质子和中子构成的微小中心核，周围有绕核运动的电子。质子数决定了原子属于哪种元素。
A molecule is a group of two or more atoms held together by chemical bonds. Some elements exist as molecules, like oxygen (O₂) and nitrogen (N₂). Compounds such as water (H₂O) and carbon dioxide (CO₂) are also made of molecules. In a chemical formula, subscript numbers show how many atoms of each type are present: CO₂ has one carbon atom and two oxygen atoms.
分子是由化学键连接在一起的两个或多个原子的组合。有些元素以分子形式存在，如氧气（O₂）和氮气（N₂）。水（H₂O）和二氧化碳（CO₂）等化合物也是由分子构成的。在化学式中，下标数字表示每种原子的个数：CO₂ 含有一个碳原子和两个氧原子。
5. Physical Change vs Chemical Change | 物理变化与化学变化
A physical change is one where no new substance is formed. The changes of state (melting, boiling, etc.) are physical changes because the particles remain the same – only their arrangement and motion change. Other examples include dissolving salt in water and cutting paper.
物理变化是指没有新物质生成的变化。状态变化（熔化、沸腾等）属于物理变化，因为粒子本身没有改变，只是排列和运动发生改变。其他例子包括盐溶于水和剪纸。
A chemical change produces one or more new substances with different properties. It is usually difficult to reverse. Chemical changes often involve energy changes – heat, light or sound may be given out or absorbed. Examples include burning wood, rusting iron and cooking food.
化学变化会产生一种或多种性质不同的新物质，通常难以逆转。化学变化常伴随能量变化——可能释放或吸收热、光或声音。例如，木材燃烧、铁生锈和烹煮食物。
6. Signs of a Chemical Reaction | 化学反应的迹象
We can tell a chemical reaction has taken place by observing certain signs. These include: a colour change, the formation of a gas (bubbles in a liquid), the formation of a solid (precipitate) when two solutions are mixed, a temperature change without external heating, and the production of light or sound.
我们可以通过观察某些迹象来判断化学反应是否发生。这些迹象包括：颜色变化、有气体生成（液体中出现气泡）、两种溶液混合后产生固体（沉淀）、无外部加热情况下的温度变化，以及产生光或声音。
It is important to remember that not all changes that produce bubbles or colour changes are chemical. However, in the lab, if several indicators appear together, it is strong evidence of a chemical reaction. For example, when magnesium metal reacts with dilute hydrochloric acid, bubbles of hydrogen gas appear and the magnesium dissolves – a clear chemical change.
需要记住并不是所有产生气泡或颜色变化的变化都是化学变化。但在实验室中，若同时出现多个迹象，便可有力地证明发生了化学反应。例如，镁金属与稀盐酸反应时，出现氢气气泡，镁溶解——这是明显的化学变化。
7. Introduction to Acids and Alkalis | 酸和碱简介
Acids are chemicals that release hydrogen ions (H⁺) in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Many acids taste sour and can be corrosive. Alkalis are bases that dissolve in water, releasing hydroxide ions (OH⁻). Sodium hydroxide (NaOH) and potassium hydroxide (KOH) are common alkalis used in the school lab.
酸是在水中释放氢离子（H⁺）的化学物质。常见的实验室酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。许多酸有酸味且具有腐蚀性。碱是溶于水释放氢氧根离子（OH⁻）的碱性物质。氢氧化钠（NaOH）和氢氧化钾（KOH）是学校实验室常用的碱。
Acids and alkalis can neutralise each other. In a neutralisation reaction, an acid reacts with an alkali to produce salt and water. For instance, hydrochloric acid + sodium hydroxide → sodium chloride + water. This type of reaction is safe enough for early practical work and helps introduce the concept of pH.
酸和碱可以相互中和。在中和反应中，酸与碱反应生成盐和水。例如，盐酸 + 氢氧化钠 → 氯化钠 + 水。这类反应安全性较高，适合早期的实践操作，并有助于引入 pH 概念。
8. pH Scale and Indicators | pH 标度及指示剂
The pH scale is a measure of how acidic or alkaline a solution is. It ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral. Pure water has a pH of 7. Acids have pH values less than 7; the lower the number, the more acidic the solution. Alkalis have pH values greater than 7; the higher the number, the more alkaline the solution.
pH 标度用于衡量溶液酸碱性的强弱。范围由 0（强酸）到 14（强碱），7 为中性。纯水的 pH 值为 7。酸的 pH 值小于 7，数值越小酸性越强。碱的 pH 值大于 7，数值越大碱性越强。
| Indicator | 指示剂 | Colour in acid | 酸性中颜色 | Colour in neutral | 中性中颜色 | Colour in alkali | 碱性中颜色 |
|---|---|---|---|---|---|---|---|
| Litmus | 石蕊 | Red | 红 | Purple | 紫 | Blue | 蓝 |
| Universal indicator | 通用指示剂 | Red, orange or yellow | 红、橙或黄 | Green | 绿 | Blue or purple | 蓝或紫 |
| Phenolphthalein | 酚酞 | Colourless | 无色 | Colourless | 无色 | Pink | 粉红 |
| Methyl orange | 甲基橙 | Red | 红 | Orange | 橙 | Yellow | 黄 |
Indicators are substances that change colour depending on the pH of the solution. Litmus paper and universal indicator solution are commonly used in the Year 7 laboratory. Universal indicator gives a range of colours across the whole pH scale and is very useful for estimating the approximate pH of an unknown solution.
指示剂是能随溶液 pH 改变颜色的物质。石蕊试纸和通用指示剂溶液在七年级实验室里常用。通用指示剂在整个 pH 标度上显示出一系列颜色，很适合用来估测未知溶液的大致 pH 值。
9. Composition of Air | 空气的组成
Air is a mixture of gases, not a compound. The main components are nitrogen (about 78%), oxygen (about 21%), argon (about 0.9%) and carbon dioxide (about 0.04%). There are also trace amounts of other gases and variable amounts of water vapour.
空气是气体混合物，不是化合物。主要成分是氮气（约 78%）、氧气（约 21%）、氩气（约 0.9%）和二氧化碳（约 0.04%）。还含有痕量的其他气体以及变化不定的水蒸气。
Oxygen is the active part of air that supports combustion and respiration. Nitrogen is relatively unreactive and helps to dilute the oxygen so that burning does not happen too quickly. The level of carbon dioxide in the atmosphere has increased over the past century due to human activities, linking this topic to environmental awareness.
氧气是空气中支持燃烧和呼吸的活性组分。氮气相对稳定，能稀释氧气，避免燃烧进行得过快。过去一个世纪，大气中二氧化碳的含量因人类活动而上升，这使得本主题与环境意识联系起来。
| Gas / 气体 | Approximate % by volume / 体积百分比（约） |
|---|---|
| Nitrogen / 氮气 | 78% |
| Oxygen / 氧气 | 21% |
| Argon / 氩气 | 0.9% |
| Carbon dioxide / 二氧化碳 | 0.04% |
| Other gases / 其他气体 | Trace / 痕量 |
10. Basic Separation Techniques | 基本分离技术
Mixtures can be separated using physical methods based on differences in physical properties. Filtration is used to separate an insoluble solid from a liquid. The mixture is poured through filter paper; the solid (residue) stays behind while the liquid (filtrate) passes through.
混合物可以根据物理性质的差异用物理方法分离。过滤用于将不溶性固体与液体分离。混合物倒入滤纸，固体（残渣）被截留，液体（滤液）则通过。
Evaporation and crystallisation separate a soluble solid from a solution. Evaporation quickly removes the solvent, leaving the solid behind, useful for substances that do not decompose on heating. Crystallisation involves gentle heating to concentrate the solution, then cooling to form crystals, which are then dried.
蒸发和结晶可将可溶性固体从溶液中分离出来。蒸发快速去除溶剂留下固体，适用于受热不易分解的物质。结晶则缓缓加热浓缩溶液，再冷却形成晶体，最后将晶体干燥。
Distillation is used to separate a liquid from a solid or two liquids with different boiling points. In simple distillation, the solution is heated; the liquid with a lower boiling point boils first, its vapour is condensed and collected. Chromatography separates different coloured substances or dyes from a mixture. A small spot of the mixture is placed on absorbent paper, which is dipped in a solvent. The components travel at different speeds and separate into spots.
蒸馏用于分离液体与固体或沸点不同的两种液体。在简单蒸馏中，加热溶液，沸点较低的液体先沸腾，其蒸气冷凝并被收集。色谱法用于分离混合物中不同颜色的物质或染料。将少量混合物点样在吸水纸上，纸的一端浸入溶剂，各组分因移动速度不同而分离成不同斑点。
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