📚 KS3 Cambridge Chemistry: Core Knowledge Review | KS3 Cambridge 化学：核心知识点梳理
Chemistry helps us understand the substances that make up everything around us and how they change. In KS3 Cambridge Science, you explore the building blocks of matter, the reactions that transform materials, and the patterns that explain the behaviour of different elements. This article brings together the core knowledge you need, from states of matter to the periodic table, acids and alkalis, and the chemistry of our planet.
化学帮助我们理解构成万物的物质以及它们如何变化。在 KS3 剑桥科学课程中，你会探索物质的基本构成单元、使材料发生转变的化学反应，以及解释不同元素行为的规律。本文汇总了核心知识点，涵盖物质状态、周期表、酸和碱，以及地球的化学。
1. States of Matter and the Particle Model | 物质状态与粒子模型
All substances are made of tiny particles. In solids, particles are packed closely in a fixed arrangement and only vibrate in place. In liquids, particles are still close but can move past each other, so liquids flow and take the shape of their container. In gases, particles are far apart and move quickly in all directions. Changes of state – melting, freezing, boiling, condensing, sublimation – can be explained by how much energy the particles have.
一切物质都由微小粒子构成。固体中，粒子紧密排列在固定位置上，只能原地振动。液体中，粒子仍然靠得很近但可以相互滑动，因此液体会流动并容器的形状。气体中，粒子相距很远，向各个方向快速运动。物质状态的变化——熔化、凝固、沸腾、凝结、升华——都可以用粒子拥有的能量多少来解释。
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. It happens faster in gases than in liquids, and faster at higher temperatures because particles have more kinetic energy. Brownian motion provides evidence for the particle model: large, visible particles such as smoke grains move randomly when bombarded by invisible gas particles.
扩散是粒子从高浓度区域向低浓度区域运动的过程。气体中的扩散比液体中快，温度越高扩散越快，因为粒子具有更大的动能。布朗运动为粒子模型提供了证据：可见的大颗粒（如烟雾颗粒）在被不可见的气体粒子撞击时会发生随机运动。
2. Inside the Atom | 原子内部
Atoms are the smallest part of an element that still has the properties of that element. An atom consists of a central nucleus made of protons and neutrons, surrounded by electrons arranged in shells. Protons have a relative charge of +1, electrons -1, and neutrons 0. Almost all the mass of the atom is in the nucleus. The atomic number (proton number) tells you how many protons an atom has, which determines the element. The mass number is the total number of protons and neutrons. Atoms are neutral because the number of electrons equals the number of protons.
原子是元素保持其性质的最小粒子。原子由中心的原子核（包含质子和中子）以及核外分层排布的电子构成。质子带相对电荷 +1，电子带 -1，中子不带电。原子的质量几乎全部集中在原子核。原子序数（质子数）表示原子所含的质子数，决定了元素种类。质量数是质子与中子的总数。原子不带电，因为电子数等于质子数。
Isotopes are atoms of the same element with different numbers of neutrons, so they have the same atomic number but different mass numbers. Electrons occupy shells: the first shell holds up to 2 electrons, the second and third shells hold up to 8 electrons each. The electronic configuration describes how electrons are arranged, e.g., sodium (Na, atomic number 11) is 2.8.1.
同位素是同一种元素的原子，它们的中子数不同，因此原子序数相同但质量数不同。电子分布在电子层上：第一层最多容纳 2 个电子，第二层和第三层最多容纳 8 个电子。电子排布描述了电子的排列方式，例如钠（Na，原子序数 11）的排布为 2.8.1。
3. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element is a substance made of only one type of atom. A compound is a substance made of two or more different types of atom chemically bonded together. A mixture contains two or more substances that are not chemically combined; each substance keeps its own properties, and they can be separated by physical methods such as filtration, distillation, chromatography, or evaporation.
元素是由同一种原子组成的物质。化合物是由两种或两种以上不同原子通过化学键结合而成的物质。混合物包含两种或多种没有经过化学结合的物质；每种物质保持自身性质，可以通过过滤、蒸馏、色谱或蒸发等物理方法分离。
Compounds have fixed compositions; for example, water is always H₂O (two hydrogen atoms and one oxygen atom). Mixtures, like air (a mixture of nitrogen, oxygen, argon, and other gases) or seawater, can have variable compositions.
化合物有固定的组成；例如水始终是 H₂O（两个氢原子和一个氧原子）。混合物，例如空气（氮气、氧气、氩气和其他气体的混合物）或海水，其组成可以变化。
4. The Periodic Table | 元素周期表
The modern periodic table arranges elements in order of increasing atomic number. The vertical columns are called groups; elements in the same group have the same number of electrons in their outer shell, which gives them similar chemical properties. The horizontal rows are called periods; as you go across a period, the number of outer electrons increases by one each time.
现代周期表按原子序数递增的顺序排列元素。纵列称为族；同一族元素最外层电子数相同，因此具有相似的化学性质。横行称为周期；从左到右，最外层电子数逐次增加一个。
Key groups include: Group 1 – alkali metals (e.g., lithium, sodium, potassium), which are highly reactive, especially with water, and have one outer electron. Group 7 – halogens (e.g., fluorine, chlorine, bromine), which are reactive non-metals with seven outer electrons. Group 0 (or 8) – noble gases (e.g., helium, neon, argon), which are unreactive because they have a full outer shell. Metals are found on the left and centre of the table, and non-metals on the right. The transition metals lie between Groups 2 and 3.
重要族包括：第 1 族——碱金属（如锂、钠、钾），非常活泼，尤其能与水反应，最外层有一个电子。第 7 族——卤素（如氟、氯、溴），是活泼的非金属，最外层有七个电子。第 0 族（或第 8 族）——稀有气体（如氦、氖、氩），通常不反应，因为最外层已满。金属位于周期表左侧和中部，非金属在右侧。过渡金属位于第 2 族与第 3 族之间。
5. Chemical Formulae and Equations | 化学式与化学方程式
oxygen atoms. Word equations describe reactions using the names of reactants and products, e.g., 'methane + oxygen → carbon dioxide + water' atoms of each element is the same on both sides, showing the law of conservation of mass.
化学符号代表元素（如 O 表示氧，Fe 表示铁）。化学式表示化合物中原子的比例：CO₂ 含有一个碳原子和两个氧原子。文字方程式用反应物和生成物的名称描述反应，例如“甲烷 + 氧气 → 二氧化碳 + 水”。符号方程式使用化学式，必须配平，使每种元素的原子数在两边相等，体现质量守恒定律。
), (l), (g), and (aq) indicate solid, liquid, gas, and aqueous solution (dissolved in water).
配平方程式需要在化学式前面加上数字。例如 H₂ + O₂ → H₂O 要配平成 2H₂ + O₂ → 2H₂O。状态符号 (s)、(l)、(g) 和 (aq) 分别表示固体、液体、气体和水溶液（溶于水中）。
6. Acids, Alkalis and Neutralisation | 酸、碱与中和反应
Acids are substances that produce hydrogen ions (H⁺) in water. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃). Alkalis are soluble bases that produce hydroxide ions (OH⁻) in water, such as sodium hydroxide (NaOH). We use indicators to test whether a solution is acidic, neutral, or alkaline. Litmus turns red in acid and blue in alkali. Universal indicator gives a pH number from 0 to 14: pH less than 7 is acidic, pH 7 is neutral, and pH greater than 7 is alkaline.
酸是在水中能产生氢离子（H⁺）的物质。实验室常见的酸有盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。碱是可溶性碱，在水中产生氢氧根离子（OH⁻），如氢氧化钠（NaOH）。我们使用指示剂检测溶液是酸性、中性还是碱性。石蕊在酸中变红，在碱中变蓝。通用指示剂给出从 0 到 14 的 pH 值：pH 小于 7 为酸性，pH 等于 7 为中性，pH 大于 7 为碱性。
um chloride + water. The general pattern is: acid + alkali → salt + water. Acid + metal carbonate → salt + water + carbon dioxide. Acid + metal → salt + hydrogen.
中和反应是酸与碱（或可溶性碱）反应生成盐和水的反应。例如：盐酸 + 氢氧化钠 → 氯化钠 + 水。一般规律为：酸 + 碱 → 盐 + 水；酸 + 金属碳酸盐 → 盐 + 水 + 二氧化碳；酸 + 金属 → 盐 + 氢气。
7. Types of Chemical Reactions | 化学反应的类型
Chemical reactions can be classified in several ways. Combustion is a rapid reaction with oxygen that releases energy as heat and light. Complete combustion of a hydrocarbon produces carbon dioxide and water. Oxidation is gain of oxygen; reduction is loss of oxygen. Thermal decomposition is when a substance breaks down into simpler substances when heated, e.g., calcium carbonate (CaCO₃) decomposes into calcium oxide (CaO) and carbon dioxide (CO₂). Displacement reactions occur when a more reactive element takes the place of a less reactive element in a compound, such as iron displacing copper from copper sulfate solution.
化学反应可以按多种方式分类。燃烧是与氧气发生的快速反应，以热和光的形式释放能量。碳氢化合物的完全燃烧生成二氧化碳和水。氧化是得到氧，还原是失去氧。热分解是物质在加热时分解成更简单物质的过程，例如碳酸钙（CaCO₃）分解为氧化钙（CaO）和二氧化碳（CO₂）。置换反应发生在较活泼的元素从化合物中取代较不活泼的元素时，例如铁从硫酸铜溶液中置换出铜。
Precipitation reactions produce an insoluble solid (a precipitate) when two solutions are mixed. Exothermic reactions transfer energy to the surroundings (temperature increases); endothermic reactions absorb energy (temperature decreases).
沉淀反应是在两种溶液混合时生成不溶性固体（沉淀）的反应。放热反应向周围环境传递能量（温度升高）；吸热反应吸收能量（温度降低）。
8. Metals, Reactivity and Extraction | 金属、活泼性与冶炼
Metals are typically shiny, good conductors of heat and electricity, malleable, and ductile. Most metals are solid at room temperature, except mercury. The reactivity series lists metals in order of their reactivity: potassium, sodium, calcium, magnesium, aluminium, zinc, iron, tin, lead, (hydrogen), copper, silver, gold, platinum. More reactive metals can displace less reactive metals from their compounds.
金属通常有光泽，是良好的导热体和导电体，具有延展性。除汞以外，大多数金属在室温下是固体。金属活动性顺序按活泼性排列：钾、钠、钙、镁、铝、锌、铁、锡、铅、（氢）、铜、银、金、铂。活泼性较强的金属可以从化合物中置换出活泼性较弱的金属。
Reactivity with water and acid helps determine the position: potassium, sodium, and calcium react vigorously with cold water; magnesium reacts slowly with cold water but faster with steam; zinc and iron react with dilute acid. Unreactive metals like gold are found native (as the element). Most metals are extracted from their ores using reduction: carbon can reduce iron oxide to iron, but for metals more reactive than carbon, electrolysis is needed.
与水及酸的反应有助于确定位置：钾、钠、钙与冷水剧烈反应；镁与冷水反应缓慢但与水蒸气反应较快；锌和铁能与稀酸反应。不活泼的金属如金以单质形式存在。大多数金属通过还原从其矿石中提取：碳可将氧化铁还原为铁，但对于比碳更活泼的金属，则需要使用电解法。
9. Earth and Atmosphere Chemistry | 地球与大气的化学
The Earth’s crust is made of rocks and minerals containing elements such as silicon, oxygen, aluminium, iron, and calcium. Igneous rocks form from cooled magma or lava (e.g., granite, basalt). Sedimentary rocks form from compressed sediments, often containing fossils (e.g., limestone, sandstone). Metamorphic rocks form when existing rocks are changed by heat and pressure (e.g., marble from limestone). The rock cycle shows how rocks change between these types over geological time.
地壳由含有硅、氧、铝、铁、钙等元素的岩石和矿物构成。火成岩由冷却的岩浆或熔岩形成（如花岗岩、玄武岩）。沉积岩由压实的沉积物形成，常含有化石（如石灰岩、砂岩）。变质岩是原有岩石在热和压力作用下发生改变而成（如大理岩源自石灰岩）。岩石循环显示了岩石如何在地质时间尺度上互相转变。
The atmosphere today is about 78% nitrogen, 21% oxygen, with small amounts of argon, carbon dioxide, and water vapour. The early atmosphere was mainly carbon dioxide with little oxygen, released by volcanoes. Oxygen levels increased due to photosynthesis by early plants and algae. Carbon dioxide dissolved in oceans, formed carbonate rocks, and was stored in fossil fuels. Human activities, such as burning fossil fuels, increase carbon dioxide levels, contributing to the enhanced greenhouse effect and climate change.
今天的大气约含 78% 氮气、21% 氧气，另有少量氩气、二氧化碳和水蒸气。早期大气主要由火山释放的二氧化碳组成，氧气极少。由于早期植物和藻类的光合作用，氧气含量逐渐升高。二氧化碳溶于海洋，形成碳酸盐岩，并储存于化石燃料中。人类活动，如燃烧化石燃料，正增加二氧化碳浓度，加剧温室效应和气候变化。
10. Practical Skills and Safety | 实验技能与安全
In KS3 chemistry, you learn to use common laboratory apparatus safely: Bunsen burner (with blue flame for heating and yellow safety flame), test tubes, beakers, measuring cylinders, conical flasks, tripod, gauze, and evaporating dish. Always wear safety goggles and follow the teacher’s instructions. When smelling a substance, use the 'wafting' technique. Learn to measure volume and mass accurately, and to read the meniscus at eye level. Filtration separates insoluble solids from liquids; evaporation and crystallisation recover dissolved solids. Chromatography separates dissolved substances based on their solubility.
在 KS3 化学课程中，你将学习安全使用常见实验器材：本生灯（蓝色火焰用于加热，黄色安全火焰）、试管、烧杯、量筒、锥形瓶、三脚架、陶土网和蒸发皿。务必佩戴护目镜并遵循老师指示。闻物质时采用“扇闻法”。学会准确测量体积和质量，并在与液面弯月面水平的位置读取刻度。过滤法分离不溶性固体和液体；蒸发与结晶法回收溶解的固体。色谱法基于溶解性差异分离溶解的物质。
Planning a simple investigation involves identifying variables: independent (the one you change), dependent (the one you measure), and control (everything kept the same). Recording observations clearly and drawing conclusions from data are essential skills. Safety symbols and hazard signs on chemical bottles help you recognise corrosive, flammable, toxic, and irritant substances.
设计简单的探究实验需要识别变量：自变量（你改变的变量）、因变量（你测量的变量）和控制变量（保持不变的所有量）。清晰地记录观察结果，并根据数据得出结论是很重要的技能。化学试剂瓶上的安全符号和危险标志帮助识别腐蚀性、易燃、有毒和刺激性物质。
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