📚 Before You Start IGCSE Chemistry | IGCSE 化学开篇基础
Welcome to IGCSE Chemistry. Before you dive into atomic structure, bonding and reactions, it is important to build a secure foundation. This opening guide covers laboratory safety, measurement, the particle model of matter and the classification of substances, so you can begin the course with confidence.
欢迎学习 IGCSE 化学。在深入学习原子结构、化学键和化学反应之前，打下扎实的基础非常重要。本篇开篇指南涵盖实验室安全、测量、物质粒子模型以及物质分类，帮助你有信心地开始这门课程。
1. Why Before You Start Matters | 为什么开篇准备很重要
IGCSE Chemistry is not just about memorising facts; it is about understanding how particles behave, how measurements are made, and how evidence is collected safely. Without these foundations, later topics such as stoichiometry, electrolysis and organic chemistry become much harder. Starting with clear definitions and practical habits gives you a strong platform for the whole course.
IGCSE 化学不只是记忆事实，而是理解粒子如何运动、如何测量以及如何安全地收集证据。没有这些基础，后续的化学计量、电解和有机化学等内容会困难得多。从清晰的定义和良好的实验习惯开始，能为整个课程打下扎实的平台。
Many exam questions test practical vocabulary and safety awareness before testing chemical theory. Examiners expect you to name apparatus, read scales correctly, and explain observations using the particle model. This introductory topic therefore carries hidden marks that students often ignore.
许多考题在考查化学理论之前，会先考查实验词汇和安全意识。考官希望你能够说出仪器名称、正确读数，并用粒子模型解释观察到的现象。因此这个入门主题含有学生经常忽略的隐性得分点。
2. Laboratory Safety Rules | 实验室安全规则
Always wear safety goggles and a lab coat during practical work. Tie back long hair, do not eat or drink in the lab, and wash your hands after handling chemicals. If a chemical spills, report it to the teacher immediately rather than trying to clean it up yourself without guidance.
实验过程中始终佩戴护目镜和实验服。长发要束起，不得在实验室饮食，接触化学品后要洗手。如果化学品溢出，立即报告老师，而不是未经指导自行清理。
Never point a test tube at yourself or others while heating it, because the contents may suddenly boil and spray out. Use a blue Bunsen flame for heating unless the procedure specifies otherwise, and always turn off the gas tap when the Bunsen burner is not in use.
加热试管时切勿将管口朝向自己或他人，因为管内物质可能突然沸腾喷出。除非操作说明另有规定，加热使用蓝色本生焰；不使用本生灯时要关闭气阀。
Read hazard symbols on reagent bottles. Common signs include flammable, corrosive, toxic and oxidising. Understanding these symbols helps you choose the correct handling method and reduces the risk of accidents.
阅读试剂瓶上的危险标志。常见标志包括易燃、腐蚀性、有毒和氧化性。理解这些符号有助于选择正确的操作方式，降低事故风险。
3. Common Apparatus and Measurement | 常用仪器与测量
You will use a measuring cylinder for approximate volumes, a burette or pipette for accurate volumes, a balance for mass, and a thermometer for temperature. Each instrument has a different precision, and you must read the bottom of the meniscus when measuring a liquid in a narrow tube.
量筒用于粗略测量体积，滴定管或移液管用于精确测量体积，天平用于称量质量，温度计用于测温。每种仪器的精密度不同，在细管中测量液体时必须读取弯月面的底部。
Digital instruments usually give a direct reading, but analogue scales require you to estimate between divisions. Always record the correct number of significant figures, including the final estimated digit, because this shows the reliability of your measurement.
数字仪器通常直接给出读数，但模拟刻度需要你在刻度之间进行估读。始终记录正确位数的有效数字，包括最后一位估读数字，因为这体现了测量结果的可靠程度。
u should be able to convert between units, for example 1000 cm³ = 1 dm³ and 1000 g = 1 kg.
化学中的温度通常以摄氏度（°C）计量。体积可以用 cm³ 或 dm³ 表示，质量以克（g）为单位。你应能进行单位换算，例如 1000 cm³ = 1 dm³，1000 g = 1 kg。
4. SI Units and Prefixes | 国际单位制与词头
IGCSE Chemistry uses SI units: kilogram (kg) for mass, metre (m) for length, second (s) for time, and kelvin (K) for thermodynamic temperature. In practice, we often use grams (g), cubic centimetres (cm³) and degrees Celsius (°C) because they are convenient for the laboratory.
IGCSE 化学使用国际单位制：质量用千克（kg），长度用米（m），时间用秒（s），热力学温度用开尔文（K）。实际实验中常用克（g）、立方厘米（cm³）和摄氏度（°C），因为它们在实验室中更方便。
nd 1 mg = 0.001 g. Being confident with these conversions prevents errors in calculations.
词头如 kilo-（10³）、centi-（10⁻²）、milli-（10⁻³）和 micro-（10⁻⁶）用于改变单位的大小。例如，1 kg = 1000 g，1 cm = 0.01 m，1 mg = 0.001 g。熟练掌握这些换算可以避免计算错误。
density = mass ÷ volume
ume. If a solid has a mass of 10 g and a volume of 5 cm³, its density is 10 ÷ 5 = 2 g/cm³.
一个有用的关系是密度。公式为密度 = 质量 ÷ 体积。如果某固体质量为 10 g，体积为 5 cm³，其密度为 10 ÷ 5 = 2 g/cm³。
5. States of Matter | 物质的三态
Matter exists mainly as solid, liquid or gas. In a solid, particles are closely packed in a regular arrangement and can only vibrate about fixed positions. In a liquid, particles are still close but can slide past one another, so the substance takes the shape of its container.
物质主要以固态、液态或气态存在。在固体中，粒子紧密排列，有规则的结构，只能在固定位置附近振动。在液体中，粒子仍然接近但可以相互滑动，因此物质会呈现容器的形状。
In a gas, particles are far apart and move rapidly in random directions. This explains why gases are easily compressed and completely fill their container. Changes between these states are physical processes: melting, freezing, boiling, condensation, sublimation and deposition.
在气体中，粒子相距很远，快速随机运动。这就解释了为什么气体容易被压缩并能完全充满容器。三态之间的变化是物理过程：熔化、凝固、沸腾、凝结、升华和凝华。
The table summarises particle arrangement, movement and spacing for each state.
下表总结了每种状态下粒子的排列方式、运动方式及间距。
- Solid: closely packed, regular, vibrate only.
- 固体：紧密排列、规则、只振动。
- Liquid: close, irregular, slide past each other.
- 液体：接近、不规则、相互滑动。
- Gas: far apart, random, fast movement.
- 气体：间距大、无规则、快速运动。
6. Kinetic Particle Theory | 粒子动理论
Kinetic particle theory states that all matter is made of tiny particles in constant motion. The higher the temperature, the greater the average kinetic energy of the particles. This theory can explain diffusion, expansion, and changes of state without needing to change the particles themselves.
粒子动理论指出，所有物质都由不断运动的微小粒子组成。温度越高，粒子的平均动能越大。该理论可以解释扩散、膨胀和状态变化，而这些过程不需要改变粒子本身。
Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. It occurs most quickly in gases, slowly in liquids, and almost imperceptibly in solids because of the differences in particle spacing and motion.
扩散是粒子从浓度较高的区域向浓度较低的区域运动。扩散在气体中最快，液体中较慢，固体中几乎难以察觉，这是由粒子间距和运动方式的差异造成的。
When a substance is heated, its particles gain kinetic energy and move farther apart, causing expansion. When cooled, particles lose kinetic energy and move closer together, causing contraction. This is a physical change because no new substance
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