📚 Year 7 CAIE Chemistry: Core Knowledge Review | Year 7 CAIE 化学：核心知识点梳理
This revision guide covers the key concepts in Year 7 CAIE Chemistry. Each topic is explained clearly with essential facts, followed by a Chinese translation to help bilingual learners master the fundamentals. Use this to reinforce your understanding and prepare effectively for assessments.
这本复习指南涵盖了 Year 7 CAIE 化学的核心概念。每个主题都用基本要点清晰解释，并附有中文翻译，帮助双语学习者掌握基础知识。用它来巩固理解，高效备考。
1. States of Matter | 物质的状态
Matter exists in three main states: solid, liquid and gas. The state depends on how the particles are arranged and how they move.
物质存在三种主要状态：固态、液态和气态。物质的状态取决于粒子的排列方式和运动方式。
In solids, particles are tightly packed in a fixed, regular pattern. They can only vibrate in place, which gives solids a definite shape and volume.
在固体中，粒子紧密排列成固定的规则图案。它们只能在原地振动，因此固体有确定的形状和体积。
In liquids, particles are still close together but not in a fixed arrangement. They can slide past each other, so liquids take the shape of their container but have a fixed volume.
在液体中，粒子彼此仍然靠近，但排列不固定。它们可以相互滑动，因此液体会呈现容器的形状，但体积固定。
In gases, particles are far apart and move randomly at high speeds. Gases have no fixed shape or volume and will spread out to fill any container.
在气体中，粒子相距很远，随机高速运动。气体没有固定的形状或体积，会扩散并充满整个容器。
2. Particle Theory | 粒子理论
The particle theory states that all matter is made of tiny particles that are constantly moving. The amount of movement depends on temperature.
粒子理论指出，所有物质都是由不断运动的微小粒子构成的。运动程度取决于温度。
Heating a substance makes its particles gain energy and move faster. This can cause a change of state, such as melting or boiling.
加热物质会使粒子获得能量，运动加快。这可能导致状态改变，例如熔化或沸腾。
The melting point is the temperature at which a solid turns into a liquid. The boiling point is the temperature at which a liquid turns into a gas.
熔点是固体变成液体的温度。沸点是液体变成气体的温度。
Diffusion is the movement of particles from an area of high concentration to an area of low concentration. It happens faster in gases than in liquids because gas particles move more freely.
扩散是粒子从高浓度区域向低浓度区域的运动。它在气体中比在液体中发生得更快，因为气体粒子的运动更自由。
3. Atoms, Elements and the Periodic Table | 原子、元素和周期表
An atom is the smallest particle of an element that can take part in a chemical reaction. Everything is made of atoms.
原子是能参与化学反应的元素的最小粒子。万物都由原子构成。
An element is a pure substance made of only one type of atom. Examples include oxygen (O), hydrogen (H) and iron (Fe).
元素是由同一种原子组成的纯净物。例如氧（O）、氢（H）和铁（Fe）。
The Periodic Table organises all known elements in order of increasing atomic number. Elements are arranged in rows (periods) and columns (groups) with similar properties.
周期表按原子序数递增的顺序排列所有已知元素。元素按周期（行）和族（列）排列，同一族的元素性质相似。
Each element has a unique chemical symbol. Metals are found on the left side of the table, while non-metals are on the right.
每种元素都有独特的化学符号。金属位于周期表左侧，非金属位于右侧。
4. Compounds and Mixtures | 化合物与混合物
A compound is formed when two or more different elements chemically combine in a fixed ratio. The properties of a compound are different from the elements that make it up.
化合物由两种或多种不同元素以固定比例化合而成。化合物的性质与组成它的元素性质不同。
For example, water (H₂O) is a compound made of hydrogen and oxygen. Sodium chloride (NaCl) is a compound made of sodium and chlorine.
例如，水（H₂O）是由氢和氧组成的化合物。氯化钠（NaCl）是由钠和氯组成的化合物。
A mixture contains two or more substances that are not chemically joined. They keep their own properties and can be separated using physical methods.
混合物含有两种或多种未发生化学结合的物质。它们保持各自的性质，可以通过物理方法分离。
Air is a mixture of gases; soil is a mixture of organic matter and minerals. Salt water is a mixture, not a compound.
空气是气体混合物；土壤是有机物和矿物的混合物。盐水是混合物，不是化合物。
5. Separation Techniques | 分离技术
Filtration is used to separate an insoluble solid from a liquid. The mixture is poured through filter paper, which traps the solid while the liquid passes through.
过滤用于将不溶性固体从液体中分离。混合物通过滤纸，滤纸截留固体，液体通过。
Evaporation removes a soluble solid from a solution by heating. The liquid evaporates, leaving the solid behind. This works well for substances like salt from salt water.
蒸发通过加热将可溶性固体从溶液中分离。液体蒸发，留下固体。这适用于从盐水中提取盐等物质。
Distillation separates a liquid from a mixture by boiling it and then condensing the vapour back into a liquid. It is useful for obtaining pure water from ink or salt solution.
蒸馏通过将液体煮沸再将蒸汽冷凝回液体，从而将液体从混合物中分离。它可用于从墨水或盐溶液中获得纯水。
Chromatography separates different dissolved substances based on how quickly they move through a medium, like paper. It can separate coloured dyes in ink.
色谱法根据不同溶解物质在介质（如纸张）中的迁移速度将其分离。它可以分离墨水中的有色染料。
6. Acids and Alkalis | 酸和碱
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They taste sour and turn blue litmus paper red. Common acids include hydrochloric acid, sulfuric acid and citric acid.
酸是溶于水时释放氢离子（H⁺）的物质。它们有酸味，使蓝色石蕊试纸变红。常见的酸有盐酸、硫酸和柠檬酸。
Alkalis are soluble bases that release hydroxide ions (OH⁻) in water. They feel soapy and turn red litmus paper blue. Examples include sodium hydroxide and calcium hydroxide.
碱是可溶的碱性物质，在水中释放氢氧根离子（OH⁻）。它们有滑腻感，使红色石蕊试纸变蓝。例如氢氧化钠和氢氧化钙。
A neutralisation reaction occurs when an acid and an alkali react together to produce a salt and water. The pH moves towards 7.
中和反应是酸和碱反应生成盐和水的过程。pH值趋向7。
Hydrochloric acid + sodium hydroxide → sodium chloride + water (HCl + NaOH → NaCl + H₂O)
盐酸 + 氢氧化钠 → 氯化钠 + 水 (HCl + NaOH → NaCl + H₂O)
7. Indicators and the pH Scale | 指示剂与pH值
An indicator is a substance that changes colour to show whether a solution is acidic or alkaline. Litmus is a common indicator.
指示剂是一种通过颜色变化显示溶液是酸性还是碱性的物质。石蕊是一种常见的指示剂。
Litmus paper turns red in acidic solutions and blue in alkaline solutions. Universal indicator gives a range of colours across the pH scale.
石蕊试纸在酸性溶液中变红，在碱性溶液中变蓝。万能指示剂在整个pH范围内显示不同的颜色。
olution is. It runs from 0 to 14: pH < 7 is acidic, pH = 7 is neutral, pH > 7 is alkaline.
pH值是衡量溶液酸碱性强弱的尺度。范围从0到14：pH < 7为酸性，pH = 7为中性，pH > 7为碱性。
The lower the pH, the stronger the acid; the higher the pH, the stronger the alkali.
pH值越低，酸性越强；pH值越高，碱性越强。
8. Metals and Non-metals | 金属与非金属
Metals are usually shiny, good conductors of heat and electricity, malleable (can be hammered into sheets) and ductile (can be drawn into wires). Most have high melting points.
金属通常有光泽，是热和电的良导体，具有可锻性（可锤打成薄片）和延性（可拉成细丝）。大多数金属熔点较高。
Non-metals are typically dull, poor conductors, and brittle when solid. They often have lower melting points and can be gases or solids at room temperature.
非金属通常暗淡，是热和电的不良导体，固态时易碎。它们通常熔点较低，室温下可为气体或固体。
Metals form basic oxides, while non-metals form acidic oxides. For example, magnesium oxide is basic; sulfur dioxide is acidic.
金属形成碱性氧化物，非金属形成酸性氧化物。例如，氧化镁是碱性的；二氧化硫是酸性的。
9. Chemical Reactions | 化学反应
A chemical reaction happens when atoms are rearranged to form new substances. The starting substances are called reactants, and the new substances are called products.
化学反应是原子重新排列形成新物质的过程。起始物质称为反应物，新物质称为生成物。
Signs of a chemical reaction include a colour change, bubbles of gas, a temperature change, or a solid (precipitate) forming when two solutions mix.
化学反应的迹象包括颜色变化、产生气泡、温度变化，或两种溶液混合时生成固体（沉淀）。
Combustion is a rapid reaction with oxygen that releases energy as heat and light. Burning fuels like methane is an example.
燃烧是与氧气发生的快速反应，以热和光的形式释放能量。甲烷等燃料的燃烧就是一个例子。
In a reaction, the total mass of reactants equals the total mass of products. This is called conservation of mass.
在化学反应中，反应物的总质量等于生成物的总质量。这称为质量守恒。
10. Physical and Chemical Changes | 物理变化与化学变化
Physical changes do not produce new chemical substances. They are often easy to reverse. Examples include changes of state (melting, freezing), cutting paper and dissolving sugar in water.
物理变化不产生新的化学物质。它们通常容易逆转。例子包括状态变化（熔化、凝固）、剪纸和糖溶于水。
Chemical changes produce one or more new substances with different properties. They are usually harder to reverse. Examples include rusting of iron, cooking an egg and burning wood.
化学变化产生一种或多种性质不同的新物质。它们通常较难逆转。例子包括铁生锈、煮鸡蛋和燃烧木材。
During a chemical change, bonds between atoms are broken and new bonds are formed. Energy is often taken in or given out.
在化学变化过程中，原子间的化学键断裂并形成新的化学键。能量通常被吸收或释放。
11. Earth's Structure and Resources | 地球结构与资源
The Earth has a layered structure: a thin rocky crust, a thick mantle, a liquid outer core and a solid inner core. These layers vary in composition and temperature.
地球具有层状构造：薄的岩石地壳、厚的地幔、液态外核和固态内核。这些层的成分和温度各不相同。
The atmosphere surrounding Earth is mainly nitrogen (about 78%) and oxygen (about 21%), with small amounts of argon, carbon dioxide and water vapour.
环绕地球的大气主要由氮气（约78%）和氧气（约21%）组成，另有少量氩气、二氧化碳和水蒸气。
Rocks are natural mixtures of minerals. The rock cycle describes how igneous, sedimentary and metamorphic rocks form and change over millions of years.
岩石是矿物的天然混合物。岩石循环描述了岩浆岩、沉积岩和变质岩如何形成以及在数百万年间发生变化。
Fossil fuels such as coal, oil and natural gas are non-renewable energy resources formed from the remains of ancient plants and animals. Burning them releases carbon dioxide.
煤、石油和天然气等化石燃料是由古代动植物遗骸形成的不可再生能源。燃烧它们会释放二氧化碳。
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