📚 Core Chemistry Concepts for Year 7 Cambridge | Year 7 Cambridge 化学：核心知识点梳理
Welcome to your complete revision guide for Year 7 Cambridge Chemistry. This article gathers all the essential topics you need to master, from states of matter and particle theory to elements, compounds, chemical reactions and separation techniques. Every section is presented in a clear bilingual format to help you study and revise effectively.
欢迎阅读 Year 7 剑桥化学完整复习指南。本文汇总了所有你必须掌握的核心知识点，涵盖物质状态、粒子理论、元素、化合物、化学反应以及分离技术。每个部分都以清晰的中英双语形式呈现，帮助你高效学习和复习。
1. States of Matter | 物质的状态
Matter exists in three main states: solid, liquid and gas. Solids have a fixed shape and a fixed volume because their particles are tightly packed in a regular pattern and can only vibrate in fixed positions. Liquids have a fixed volume but take the shape of their container; their particles are close together but can slide past each other. Gases have no fixed shape or volume and will spread out to fill any container; gas particles are far apart and move rapidly in all directions.
物质主要以三种状态存在：固态、液态和气态。固体有固定的形状和体积，因为其粒子紧密排列成规则结构，只能在固定位置振动。液体有固定的体积但会随着容器改变形状；液体粒子聚集在一起，但可以相互滑动。气体没有固定的形状或体积，会扩散并充满整个容器；气体粒子相距很远，并且向各个方向快速运动。
Everyday examples include ice (solid water), liquid water, and water vapour (steam) as a gas. The particle model helps explain why substances behave differently in each state.
日常例子包括冰（固态水）、液态水和水蒸气（气态水）。粒子模型能帮助解释为什么物质在不同状态下表现不同。
2. Particle Theory | 粒子理论
All matter is made up of extremely tiny particles that are in constant motion. The amount of energy these particles have determines whether the substance is a solid, liquid or gas. When a substance is heated, the particles gain kinetic energy and move more vigorously. This extra movement can overcome the attractive forces between them, leading to a change of state.
所有物质都是由不断运动的极小微粒构成的。粒子所具有的能量大小决定了该物质是固态、液态还是气态。物质受热时，粒子获得动能，运动变得更加剧烈。这种额外的运动能够克服粒子间的相互吸引力，从而导致状态改变。
In solids, particles vibrate in fixed positions; in liquids, they move around each other while staying close; in gases, they move randomly and independently at high speeds.
在固体中，粒子在固定位置振动；在液体中，粒子相互围绕运动但仍紧密聚集；在气体中，粒子高速随机独立运动。
3. Changes of State | 状态变化
Substances can change from one state to another through physical processes. Melting turns a solid into a liquid, freezing turns a liquid into a solid, boiling (or evaporation) turns a liquid into a gas, and condensation turns a gas back into a liquid. Sublimation is the direct change from solid to gas, such as solid carbon dioxide (dry ice).
物质可以通过物理过程从一种状态转变为另一种状态。融化使固体变为液体，凝固使液体变为固体，沸腾（或蒸发）使液体变为气体，冷凝使气体变回液体。升华是指固体直接变成气体，例如固态二氧化碳（干冰）的变化。
During a change of state, the temperature of the substance remains constant until the change is complete. The energy supplied is used to break or form the forces between particles, not to raise the temperature. The melting point and boiling point are characteristic physical properties of a pure substance.
在状态变化过程中，物质的温度会保持不变，直到变化完成。此时输入的能量用于打破或形成粒子间的作用力，而不是升高温度。熔点和沸点是纯净物质的特征物理性质。
4. Physical and Chemical Changes | 物理变化与化学变化
A physical change does not produce any new substances and is often easy to reverse. Examples include melting ice, dissolving salt in water, and tearing paper. In a physical change, no chemical bonds are broken or formed.
物理变化不产生新物质，通常容易逆转。例如冰融化、食盐溶于水、撕纸等。在物理变化中，没有化学键断裂或形成。
A chemical change (chemical reaction) produces one or more new substances with different properties from the starting materials. Chemical changes are usually irreversible under simple conditions. Typical signs of a chemical reaction include a colour change, the formation of a gas (bubbles), a temperature change (heat released or absorbed), and the appearance of a precipitate (an insoluble solid).
化学变化（化学反应）会产生一种或多种性质不同于原来物质的新物质。化学变化在简单条件下通常不可逆。化学反应的典型迹象包括颜色变化、产生气体（气泡）、温度变化（放热或吸热）以及沉淀（不溶性固体）的生成。
Examples of chemical changes are burning wood, frying an egg, rusting iron and cooking food.
化学变化的例子有：木材燃烧、煎蛋、铁生锈和烹饪食物。
5. Elements, Compounds and Mixtures | 元素、化合物和混合物
An element is a pure substance made of only one kind of atom. Examples include oxygen (O), hydrogen (H) and iron (Fe). A compound is a pure substance formed when two or more different elements are chemically bonded together. The properties of a compound are different from the elements it contains. For example, water (H₂O) is a liquid, but hydrogen and oxygen are gases. A mixture contains two or more substances that are not chemically combined, so each substance keeps its own properties. Air is a mixture of gases, and seawater is a mixture of water and dissolved salts.
元素是由同一种原子组成的纯净物，例如氧（O）、氢（H）和铁（Fe）。化合物是由两种或多种不同元素通过化学键结合而成的纯净物。化合物的性质与它所含的元素不同。例如，水（H₂O）是液体，而氢和氧都是气体。混合物包含两种或多种未发生化学结合的物质，因此各物质都保持自己的性质。空气是多种气体的混合物，海水是水和溶解盐的混合物。
| Feature | Element | Compound | Mixture |
|---|---|---|---|
| Composition | One type of atom | Two or more different atoms chemically bonded | Two or more substances not chemically bonded |
| Separation | Cannot be broken down by physical methods | Can only be separated by chemical reactions | Easily separated by physical methods |
| Properties | Distinct properties of that element | Totally different from its elements | Each component keeps its own properties |
6. The Periodic Table | 元素周期表
The Periodic Table is a chart that organises all known elements in order of increasing atomic number. Elements are arranged in horizontal rows called periods and vertical columns called groups. Elements in the same group share similar chemical properties because they have the same number of electrons in their outer shell.
元素周期表是一张按原子序数递增排列所有已知元素的图表。元素排成横行称为周期，纵列称为族。同一族的元素具有相似的化学性质，因为它们的原子最外层电子数相同。
Metals are found on the left and in the centre of the table, while non-metals are located on the right. Some important groups for Year 7 include Group 1 (alkali metals, very reactive), Group 7 (halogens, reactive non-metals) and Group 0 or 8 (noble gases, unreactive).
金属位于周期表的左侧和中部，非金属位于右侧。七年级需要了解的一些重要族包括第1族（碱金属，非常活泼）、第7族（卤素，活泼的非金属）和第0族或第8族（稀有气体，不活泼）。
7. Acids and Alkalis | 酸与碱
Acids are substances that have a sour taste and are corrosive. In the laboratory, common acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Acids turn blue litmus paper red. Alkalis are soluble bases that feel soapy and are also corrosive. Common alkalis include sodium hydroxide (NaOH) and potassium hydroxide (KOH). Alkalis turn red litmus paper blue.
酸是有酸味且具有腐蚀性的物质。实验室中常见的酸有盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。酸能使蓝色石蕊试纸变红。碱是可溶于水的碱性物质，有滑腻感且同样具有腐蚀性。常见的碱包括氢氧化钠（NaOH）和氢氧化钾（KOH）。碱能使红色石蕊试纸变蓝。
The pH scale measures how acidic or alkaline a solution is. It ranges from 0 to 14. A pH less than 7 indicates an acidic solution, pH 7 is neutral (like pure water), and a pH greater than 7 indicates an alkaline solution. Universal indicator shows a range of colours across the scale.
pH 值用于衡量溶液的酸碱程度，范围从 0 到 14。pH 小于 7 表示酸性溶液，pH 等于 7 为中性（如纯水），pH 大于 7 表示碱性溶液。通用指示剂能在此范围内显示不同的颜色。
8. Neutralisation | 中和反应
Neutralisation is a chemical reaction between an acid and an alkali (or base) that produces a salt and water. The general word equation is:
中和反应是酸与碱发生反应生成盐和水的化学反应。一般文字表达式为：
acid + alkali → salt + water
酸 + 碱 → 盐 + 水
For example, when hydrochloric acid reacts with sodium hydroxide, the products are sodium chloride (common table salt) and water:
例如，盐酸与氢氧化钠反应时，生成氯化钠（食盐）和水：
HCl + NaOH → NaCl + H₂O
Neutralisation is used in many everyday contexts, such as treating acidic soil with lime (calcium hydroxide) and taking antacid tablets to relieve indigestion caused by excess stomach acid.
中和反应在日常生活中的应用很多，例如用石灰（氢氧化钙）改良酸性土壤，以及服用抗酸药片缓解胃酸过多引起的消化不良。
9. Separation Techniques | 分离技术
Mixtures can be separated into their components using physical methods that exploit differences in physical properties. Filtration is used to separate an insoluble solid from a liquid, for example sand from water. The mixture is poured through filter paper; the solid stays on the paper as the residue while the liquid passes through as the filtrate.
混合物可利用各组分物理性质的差异，通过物理方法进行分离。过滤用来分离不溶性固体和液体，例如从水中分离沙子。将混合物倒入滤纸，固体会留在滤纸上成为残渣，液体则穿过滤纸成为滤液。
Evaporation can be used to obtain a dissolved solid from a solution. Heating the solution causes the solvent (usually water) to evaporate, leaving the solid behind. Distillation goes a step further: the solvent is boiled, and the vapour is cooled and condensed back into a liquid, collecting a pure solvent. This is how pure water is obtained from seawater.
蒸发可用于从溶液中获取溶解的固体。加热溶液使溶剂（通常是水）蒸发，留下固体。蒸馏则更进一步：将溶剂煮沸，使产生的蒸气冷却并冷凝回液体，从而收集到纯净的溶剂。这就是从海水中获取纯水的方法。
Chromatography separates different coloured substances within a mixture, such as the dyes in ink. A small spot of the mixture is placed on chromatography paper, which is dipped in a solvent. As the solvent travels up, the dyes move at different rates and separate. Magnetism can separate magnetic materials like iron from non-magnetic ones.
色谱法用于分离混合物中不同颜色的物质，如墨水中的色素。将一小点混合物点在层析纸上，然后把纸的一端浸入溶剂。随着溶剂向上移动，色素以不同速度移动并实现分离。磁性分离则利用磁铁将铁等磁性材料从非磁性材料中分离出来。
10. Air and Combustion | 空气与燃烧
Air is not a single substance but a mixture of gases. The main components are nitrogen (about 78%) and oxygen (about 21%). The remaining 1% includes carbon dioxide, water vapour and noble gases such as argon. Oxygen is the gas that supports combustion and is essential for life.
空气不是单一物质，而是多种气体的混合物。主要成分是氮气（约占 78%）和氧气（约占 21%）。剩下的 1% 包括二氧化碳、水蒸气和氩等稀有气体。氧气是支持燃烧并维持生命必需的气体。
Combustion, or burning, is a chemical reaction in which a substance reacts rapidly with oxygen, releasing energy in the form of heat and light. For combustion to happen, three things must be present at the same time: a fuel, heat (to reach the ignition temperature) and oxygen. This is often represented by the fire triangle. Removing any one of these stops the fire.
燃烧是一种化学反应，物质与氧气快速反应，以热和光的形式释放能量。发生燃烧必须同时具备三个条件：燃料、热量（达到着火点）和氧气。这通常用燃烧三角来表示。去除三角中的任何一角，燃烧就会停止。
The burning of a hydrocarbon fuel in plenty of oxygen produces carbon dioxide and water:
碳氢燃料在充足氧气中燃烧会生成二氧化碳和水：
fuel + oxygen → carbon dioxide + water
燃料 + 氧气 → 二氧化碳 + 水
11. Metals and Non-metals | 金属与非金属
Metals are found mostly on the left side of the Periodic Table and have characteristic physical properties. They are typically shiny (lustrous), good conductors of heat and electricity, malleable (can be hammered into sheets) and ductile (can be drawn into wires). Most metals are solid at room temperature, except mercury, which is a liquid.
金属主要位于周期表的左侧，具有特征性的物理性质。金属通常有光泽，是热和电的良导体，具有延展性（可锤打成薄片）和韧性（可拉成丝）。绝大多数金属在室温下为固体，只有汞是液体。
Non-metals are generally found on the right side of the Periodic Table. They are often dull, poor conductors of heat and electricity, and brittle if solid. Examples of non-metals include oxygen, carbon, sulfur and chlorine. Many non-metals are gases at room temperature.
非金属一般位于周期表的右侧，通常无光泽，是热和电的不良导体，固体时往往易碎。非金属的例子包括氧、碳、硫和氯。许多非金属在室温下为气体。
Some metals react vigorously with acids, producing hydrogen gas and a salt. This reactivity varies: potassium and sodium react explosively, while copper does not react with dilute acids at all. This idea introduces the concept of the reactivity series, which ranks metals according to their ability to react.
有些金属能与酸剧烈反应，产生氢气和盐。这种活泼性各不相同：钾和钠反应会爆炸，而铜则完全不与稀酸反应。这一概念引出了金属活动性顺序，即根据金属的反应能力强弱排序。
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