📚 Year 7 OCR Chemistry: Key Knowledge Revision | 7年级OCR化学：核心知识点梳理
Welcome to your essential Year 7 OCR Chemistry revision guide. Chemistry is the science that explains what substances are made of, how they behave and how they change. This article brings together all the core ideas you need to understand, from the tiny particles that make up everything around you, to acids, alkalis and important chemical reactions. Read through each section carefully, check your understanding and build a strong foundation for further study.
欢迎来到你必备的7年级OCR化学复习指南。化学是解释物质组成、性质及其变化方式的科学。本文汇总了你需要理解的所有核心概念，从构成万物的微小粒子，到酸、碱和重要的化学反应。请仔细阅读每一部分，检查你的理解，为进一步的学习打下坚实基础。
1. States of Matter and Particle Model | 物质的状态与粒子模型
All matter is made up of tiny, constantly moving particles. The way these particles are arranged and how they move determines whether a substance is a solid, liquid or gas.
所有物质都由微小且不断运动的粒子构成。这些粒子的排列方式和运动状态决定了物质是固体、液体还是气体。
In solids, particles are packed tightly in a regular, fixed arrangement. They can only vibrate in place, so a solid has a definite shape and a fixed volume.
在固体中，粒子紧密、规则地排列并固定不动。它们只能在原位振动，因此固体具有确定的形状和固定的体积。
In liquids, particles are still close together but can slide past one another. A liquid has a fixed volume but takes the shape of the bottom of its container.
在液体中，粒子仍然紧密相依，但可以相互滑动。液体有固定的体积，但形状随容器底部改变。
In gases, particles are far apart and move rapidly in all directions. A gas has no fixed shape or volume and can spread out to fill any space. Gases can be easily compressed because there is lots of space between the particles.
在气体中，粒子相距很远，并向各个方向快速运动。气体没有固定形状或体积，会扩散充满任何空间。由于粒子间有大量空隙，气体容易被压缩。
2. Changes of State | 状态变化
When a substance is heated or cooled, it can change from one state to another. These are physical changes — no new substance is made, and the change can usually be reversed.
物质受热或冷却时，可以从一种状态变为另一种状态。这些变化是物理变化——没有新物质生成，且变化通常可逆。
Melting (solid to liquid) and boiling or evaporating (liquid to gas) need energy to be supplied. Freezing (liquid to solid) and condensing (gas to liquid) release energy to the surroundings.
熔化（固体变液体）和沸腾或蒸发（液体变气体）需要吸收能量。凝固（液体变固体）和冷凝（气体变液体）向周围释放能量。
Sublimation is when a solid turns directly into a gas without passing through the liquid state, such as solid carbon dioxide (dry ice) turning into carbon dioxide gas.
升华是指固体不经过液态直接变为气体，例如固态二氧化碳（干冰）变成二氧化碳气体。
Mass is conserved during all changes of state. The total number of particles does not change; they simply become arranged differently.
在所有状态变化过程中，质量守恒。粒子总数不变，只是排列方式发生改变。
3. Atoms, Elements and Compounds | 原子、元素和化合物
An atom is the smallest particle of an element that can exist. Everything in the universe is built from about 100 different types of atoms.
原子是元素能够存在的最小粒子。宇宙万物都由大约100种不同类型的原子构成。
An element is a substance made from only one type of atom. Examples are oxygen (O), iron (Fe) and helium (He). All known elements are listed on the Periodic Table.
元素是只由一种原子组成的物质。例如氧（O）、铁（Fe）和氦（He）。所有已知元素都列在元素周期表中。
A compound forms when atoms of two or more different elements chemically combine in fixed ratios. The compound has different properties from the elements that make it. For example, water (H₂O) is a liquid, but hydrogen and oxygen are gases.
当两种或更多不同元素的原子以固定比例化学结合时，就形成了化合物。化合物的性质与组成它的元素不同。例如，水（H₂O）是液体，而氢和氧是气体。
A chemical reaction is needed to break the bonds in a compound and free the separate elements. Simple heating usually isn't enough.
要打破化合物中的化学键并分离出元素，通常需要发生化学反应。单纯加热往往不够。
4. The Periodic Table | 元素周期表
The Periodic Table organises all elements in order of increasing atomic number (the number of protons in the nucleus). It is an incredibly useful tool for chemists.
元素周期表按原子序数（原子核中质子的数量）递增的顺序排列所有元素。它是化学家极其实用的工具。
Horizontal rows are called periods. Vertical columns are called groups. Elements in the same group have similar chemical properties because they have the same number of electrons in their outer shell.
横排称为周期，纵列称为族。同一族的元素化学性质相似，因为它们最外层电子数相同。
Metals are found on the left and centre of the table; they are shiny, conduct heat and electricity, and are often malleable. Non-metals are on the right and tend to be dull and brittle. A stepped line helps separate the two.
金属位于周期表左侧和中部；它们有光泽、能导热和导电，通常具有延展性。非金属位于右侧，往往暗淡而脆。一条阶梯线将两者大致分开。
5. Chemical Symbols and Formulae | 化学符号与化学式
Every element is given a unique chemical symbol, usually one or two letters. The first letter is always a capital letter. If a second letter is used, it is always lowercase. Examples: C for carbon, O for oxygen, Na for sodium, Fe for iron.
每种元素都有一个独特的化学符号，通常由一个或两个字母组成。第一个字母总是大写。如果有第二个字母，则始终小写。例如：C代表碳，O代表氧，Na代表钠，Fe代表铁。
A chemical formula uses symbols and subscript numbers to show the types and numbers of atoms in a compound. For instance, H₂O tells us there are two hydrogen atoms and one oxygen atom in a water molecule.
化学式使用符号和下标数字来表明化合物中原子的种类和数量。例如，H₂O告诉我们一个水分子中有两个氢原子和一个氧原子。
If a formula has no subscript, it means there is one atom of that element. In CO₂, there is one carbon atom and two oxygen atoms. In NaCl, there is one sodium ion for each chloride ion.
如果化学式中没有下标，则表示该元素有一个原子。在CO₂中，有一个碳原子和两个氧原子。在NaCl中，每个氯离子对应一个钠离子。
6. Pure Substances and Mixtures | 纯净物与混合物
A pure substance consists of only one type of particle — either a single element or a single compound. Pure substances melt and boil at specific, fixed temperatures.
纯净物只含有一种粒子——要么是单一元素，要么是单一化合物。纯净物在特定的固定温度下熔化和沸腾。
A mixture contains two or more different substances that are not chemically bonded together. The components can be present in any proportion and keep their own individual properties.
混合物包含两种或更多没有通过化学键结合的不同物质。各组分可按任意比例存在，并保持各自原有的性质。
Air is a mixture of gases, mainly nitrogen (N₂), oxygen (O₂) and small amounts of others. Seawater and soil are also mixtures. Mixtures melt and boil over a range of temperatures, not at one exact point.
空气是气体混合物，主要有氮气（N₂）、氧气（O₂）及少量其他气体。海水和土壤也是混合物。混合物在一个温度范围内熔化或沸腾，而不是在精确的某一温度。
7. Separation Techniques | 分离技术
Because mixtures are not chemically combined, their parts can be separated using physical methods. The choice of technique depends on the properties of the substances in the mixture.
由于混合物中各组分没有化学结合，可以使用物理方法将其分离。选择何种技术取决于混合物中物质的性质。
Filtration separates an insoluble solid from a liquid. The mixture is poured through filter paper; the solid is trapped as the residue, and the liquid that passes through is called the filtrate.
过滤用于分离不溶性固体和液体。将混合物倒在滤纸上，固体被拦截成为残渣，通过的液体叫作滤液。
Evaporation removes a solvent from a solution, leaving the solid solute behind. If careful, slow cooling is used, crystals of the solid can be obtained — this is crystallisation.
蒸发从溶液中除去溶剂，留下固态溶质。如果采用小心的缓慢冷却，则可获得该固体的晶体——这就是结晶法。
Simple distillation separates a liquid from a solution by boiling the liquid and then condensing the vapour back into liquid. The pure liquid collected is the distillate. Chromatography can separate coloured mixtures, such as inks, based on how well each dye dissolves in a solvent and sticks to paper.
简单蒸馏通过煮沸液体然后冷凝蒸气将液体从溶液中分离出来。收集到的纯液体是馏出液。色谱法可以根据不同染料在溶剂中的溶解度及其在纸上的吸附程度来分离有色混合物，例如墨水。
8. Acids and Alkalis | 酸与碱
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Many fruits contain natural acids, such as citric acid in lemons.
酸是溶于水时释放出氢离子（H⁺）的物质。常见的实验室酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。许多水果含有天然酸，例如柠檬中的柠檬酸。
Alkalis are soluble bases that release hydroxide ions (OH⁻) in water. Examples are sodium hydroxide (NaOH) and potassium hydroxide (KOH). Household alkalis include soap, bleach and bicarbonate of soda.
碱是可溶性碱，在水中会释放出氢氧根离子（OH⁻）。例如氢氧化钠（NaOH）和氢氧化钾（KOH）。家用碱包括肥皂、漂白剂和小苏打。
Both acids
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