📚 KS3 Chemistry Unit 9 Review: Matter, Reactions and Earth | KS3化学第九单元复习：物质、反应与地球
Welcome to the Unit 9 chemistry review for KS3. This guide brings together the key ideas you need for tests: from the particle model to elements, compounds, chemical reactions and Earth science.
欢迎使用 KS3 化学第九单元复习。本指南汇集了考试所需的关键概念：从粒子模型到元素、化合物、化学反应和地球科学。
1. The Particle Model | 粒子模型
All matter is made of tiny particles. The particle model explains the properties of solids, liquids and gases by differences in particle arrangement, movement and energy.
所有物质都由微小粒子组成。粒子模型通过粒子排列、运动和能量的差异来解释固体、液体和气体的性质。
In a solid, the particles are tightly packed in a regular pattern. They vibrate in fixed positions but cannot move freely, which is why solids keep their shape.
在固体中，粒子紧密排列成规则结构。它们只能在固定位置振动，不能自由移动，因此固体会保持自己的形状。
In a liquid, the particles are close together but are arranged in a disordered way. They can slide over each other, so liquids can flow and take the shape of a container.
在液体中，粒子彼此靠近，但排列不规则。它们可以相互滑动，因此液体能够流动并呈现容器的形状。
In a gas, the particles are far apart and move quickly in all directions. This is why gases spread out to fill the whole space they are in.
在气体中，粒子相距很远，并向各个方向快速运动。这就是气体会扩散并充满所在空间的原因。
2. States of Matter and Changes of State | 物质状态与状态变化
Changing state is a physical process. Melting, freezing, boiling, condensing and sublimation happen when particles gain or lose energy, not when new substances are formed.
状态变化是物理过程。熔化、凝固、沸腾、冷凝和升华发生时，粒子获得或失去能量，并不是生成新物质。
When a solid is heated, its particles gain energy and vibrate more. At the melting point, the particles have enough energy to break away from their fixed positions and form a liquid.
当固体被加热时，粒子获得能量并振动得更剧烈。达到熔点时，粒子拥有足够的能量脱离固定位置，形成液体。
When a liquid is heated to its boiling point, particles gain enough energy to escape from the surface and throughout the liquid as gas bubbles. This is boiling.
当液体被加热到沸点时，粒子获得足够的能量，从液体表面和内部以气泡形式逸出成为气体。这就是沸腾。
Condensation is the opposite of boiling. Gas particles lose energy, slow down and move closer together to form a liquid.
冷凝是沸腾的相反过程。气体粒子失去能量、运动减慢，彼此靠近形成液体。
3. Atoms, Elements and Compounds | 原子、元素和化合物
An element contains only one type of atom. A compound contains two or more different elements chemically joined in fixed proportions. A mixture contains substances that are not chemically bonded.
元素只含有一种原子。化合物含有两种或两种以上不同元素，以固定比例化学结合。混合物中的物质没有化学键合。
For example, oxygen gas O₂ is an element, water H₂O is a compound, and air is a mixture of gases. Compounds have different properties from the elements they are made from.
例如，氧气 O₂ 是单质，水 H₂O 是化合物，空气是气体混合物。化合物的性质与其组成元素不同。
In a mixture such as salt water, the salt and water keep their own properties and can be separated by physical methods such as evaporation.
在像盐水这样的混合物中，盐和水保持各自的性质，并且可以通过蒸发等物理方法进行分离。
In a compound, the elements are chemically combined. Water is very different from the hydrogen and oxygen gases that make it up.
在化合物中，元素以化学方式结合。水与构成它的氢气和氧气在性质上非常不同。
4. Chemical Symbols and Formulae | 化学符号与化学式
Each element has a chemical symbol, such as H for hydrogen, O for oxygen, Na for sodium and Fe for iron. Symbols with two letters always have a capital first letter and a lower-case second letter.
每种元素都有化学符号，例如 H 代表氢、O 代表氧、Na 代表钠、Fe 代表铁。两个字母的符号首字母必须大写，第二个字母小写。
A formula shows the number of each atom in a compound. H₂O means two hydrogen atoms and one oxygen atom; CO₂ means one carbon atom and two oxygen atoms.
化学式表示化合物中各原子的数目。H₂O 表示两个氢原子和一个氧原子；CO₂ 表示一个碳原子和两个氧原子。
H₂O CO₂ NaCl
These are chemical formulae for water, carbon dioxide and sodium chloride. The small subscript numbers show how many atoms of each element are present.
这些分别是水、二氧化碳和氯化钠的化学式。右下角的小数字表示每种元素原子的个数。
5. Physical and Chemical Changes | 物理变化和化学变化
In a physical change no new substance is made. Changes such as dissolving salt in water, melting ice and cutting paper are usually easy to reverse.
物理变化中没有新物质生成。例如食盐溶于水、冰熔化和剪纸通常容易逆转。
In a chemical change new substances are formed and the change is often difficult to reverse. Signs of a chemical reaction include colour change, gas bubbles, temperature change, precipitate formation or light.
化学变化中会生成新物质，变化通常难以逆转。化学反应的迹象包括颜色变化、气泡、温度变化、生成沉淀或发光。
Examples of chemical reactions are burning magnesium, rusting iron and adding acid to carbonate rocks such as limestone.
化学反应的例子有镁条燃烧、铁生锈和酸与石灰石等碳酸盐岩石反应。
Rusting is a slow chemical reaction between iron, oxygen and water. It produces hydrated iron oxide, which is flaky and weak.
生锈是铁、氧气和水之间发生的缓慢化学反应。它生成水合氧化铁，这种物质呈片状且不牢固。
6. Acids, Alkalis and Indicators | 酸、碱和指示剂
Acids have a pH less than 7, alkalis have a pH greater than 7, and a neutral solution has a pH of 7. Common acids include hydrochloric acid, sulfuric acid and citric acid.
酸的 pH 小于 7，碱的 pH 大于 7，中性溶液的 pH 等于 7。常见酸包括盐酸、硫酸和柠檬酸。
Indicators change colour to show whether a solution is acidic, neutral or alkaline. Litmus turns red in acid and blue in alkali. Universal indicator gives a range of colours from red to violet.
指示剂通过颜色变化来显示溶液是酸性、中性还是碱性。石蕊在酸中变红，在碱中变蓝。通用指示剂呈现从红到紫的一系列颜色。
Alkalis are soluble bases. Common alkalis include sodium hydroxide, potassium hydroxide and calcium hydroxide.
碱是可溶性的碱。常见碱包括氢氧化钠、氢氧化钾和氢氧化钙。
| Indicator | Acid colour | Neutral colour | Alkali colour |
| Litmus | red | purple | blue |
| Universal indicator | red / orange / yellow | green | blue / violet |
The table shows how different indicators change colour in acidic, neutral and alkaline solutions. Use universal indicator to estimate the pH of an unknown solution.
该表显示了不同指示剂在酸性、中性和碱性溶液中的颜色变化。可以使用通用指示剂估计未知溶液的 pH 值。
7. Neutralisation and Salts | 中和反应与盐
When an acid reacts with an alkali, a neutralisation reaction takes place. The general word equation is shown below.
酸与碱发生中和反应。一般文字方程式如下所示。
acid + alkali → salt + water
中文对应：酸 + 碱 → 盐 + 水。
roxide → sodium chloride + water. The pH moves towards 7 when the right amounts are mixed.
例如，盐酸 + 氢氧化钠 → 氯化钠 + 水。当按适量混合时，pH 会向 7 移动。
Acids also react with metal carbonates to produce a salt, water and carbon dioxide gas. This reaction is used to test for carbonate rocks because the gas turns limewater milky.
酸还与金属碳酸盐反应生成盐、水和二氧化碳气体。这个反应可用于检验碳酸盐岩石，因为产生的气体会使石灰水变浑浊。
acid + metal carbonate → salt + water + carbon dioxide
中文对应：酸 + 金属碳酸盐 → 盐 + 水 + 二氧化碳。
8. Metals and Their Reactions | 金属及其反应
Metals are found on the left and centre of the periodic table. They are often shiny, good conductors of heat and electricity, malleable and ductile.
金属位于周期表的左侧和中部。金属通常有光泽，是热和电的良导体，具有延展性和延性。
Metals react with acids to produce a salt and hydrogen gas. A burning splint gives a squeaky pop when hydrogen is present.
金属与酸反应生成盐和氢气。点燃的小木条遇到氢气会发出爆鸣声。
metal + acid → salt + hydrogen
中文对应：金属 + 酸 → 盐 + 氢气。
Different metals react at different rates. Magnesium reacts quickly with dilute acid, zinc reacts steadily, and copper does not react with most dilute acids.
不同金属的反应速率不同。镁与稀酸反应迅速，锌反应平稳，而铜与大多数稀酸不反应。
9. The Reactivity Series and Displacement | 金属活动性顺序与置换反应
The reactivity series lists metals in order of how vigorously they react. A common KS3 order is: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, hydrogen, copper, silver, gold.
金属活动性顺序按金属反应的剧烈程度排列。KS3 常见的顺序是：钾、钠、钙、镁、铝、锌、铁、铅、氢、铜、银、金。
A more reactive metal can displace a less reactive metal from its compound. For example, zinc displaces copper from copper sulfate solution.
较活泼的金属可以从较不活泼金属的化合物中置换出该金属。例如，锌从硫酸铜溶液中置换出铜。
zinc + copper sulfate → zinc sulfate + copper
中文对应：锌 + 硫酸铜 → 硫酸锌 + 铜。
Displacement reactions often show a colour change and a temperature rise. The blue copper sulfate solution fades as copper metal is deposited.
置换反应通常伴有颜色变化和温度升高。随着铜金属析出，蓝色的硫酸铜溶液颜色变浅。
10. Earth's Atmosphere and Resources | 地球大气与资源
Earth's early atmosphere was very different from today's air. Today, dry air is about 78% nitrogen, 21% oxygen and about 1% other gases including argon and carbon dioxide.
地球早期的大气与今天的空气很不同。现在干燥空气约含 78% 氮气、21% 氧气和约 1% 的其他气体，包括氩和二氧化碳。
Carbon dioxide is released by burning fossil fuels, respiration and thermal decomposition of limestone. Excess CO₂ is linked to climate change and ocean acidification.
燃烧化石燃料、呼吸作用和石灰石的热分解都会释放二氧化碳。过
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