📚 IGCSE Chemistry Subject Content | IGCSE 化学学科内容概览
This guide outlines the main IGCSE Chemistry subject content, linking key concepts to common exam tasks. It is designed for revision and a quick check of the syllabus core. Each section pairs the theory you must know with the wording examiners expect, so you can move from understanding to marks.
本指南概述 IGCSE 化学学科主要内容，将关键概念与常见考题联系起来，适合复习和快速检查大纲核心。每一节都把必须掌握的理论与考官期待的表述配对呈现，帮助你从"看懂"走到"拿分"。
The order below follows the way most syllabuses build up ideas: particles first, then atoms, then bonding, then calculations and reactions, and finally the applied topics of electrolysis and organic chemistry. Use it as a checklist: if you can explain each heading aloud in your own words, you are ready for structured questions.
以下顺序遵循大多数大纲构建知识的方式：先讲粒子，再讲原子，再讲化学键，然后是计算与反应，最后是电解与有机化学等应用主题。把它当作清单使用：如果你能用自己的话口头解释每一个标题，那么结构题你已经准备好了。
1. States of Matter | 物质状态
The kinetic particle model explains solids, liquids and gases. Melting, boiling, condensation, freezing, sublimation and diffusion all depend on particle motion and spacing. In this model every substance is made of tiny particles in constant random motion, and the state depends on the balance between the kinetic energy of the particles and the attractive forces between them.
动理粒子模型解释固态、液态和气态。熔化、沸腾、冷凝、凝固、升华和扩散都取决于粒子的运动与间距。在该模型中，一切物质都由不断做无规则运动的微小粒子构成，物质状态取决于粒子动能与粒子间吸引力之间的平衡。
Heating a solid gives particles more kinetic energy until they overcome the attractive forces. Diffusion is faster in gases than liquids because there is more space for particles to travel. Raising the temperature also speeds up diffusion, and lighter particles diffuse faster than heavier ones under the same conditions.
加热固体使粒子获得更多动能，直到克服吸引力。气体中的扩散比液体中快，因为粒子有更多运动空间。升高温度同样会加快扩散，而在相同条件下，较轻的粒子比更重的粒子扩散得更快。
- Solid: fixed shape and volume; particles vibrate in fixed positions.
固态：形状和体积固定；粒子在固定位置振动。 - Liquid: fixed volume but takes the shape of the container; particles slide past one another.
液态：体积固定但形状随容器；粒子相互滑动。 - Gas: no fixed shape or volume; particles move rapidly and are widely spaced.
气态：无固定形状或体积；粒子快速运动且间距很大。
The classic diffusion experiment uses a glass tube with cotton wool soaked in concentrated ammonia solution at one end and concentrated hydrochloric acid at the other. A white ring of ammonium chloride forms nearer the acid end, proving that ammonia molecules are lighter and diffuse faster. State changes are physical changes: the particles themselves do not change, only their arrangement and energy.
经典的扩散实验使用一根玻璃管，一端放浸过浓氨水的棉花，另一端放浸过浓盐酸的棉花。白色氯化铵环出现在靠近盐酸的一端，证明氨分子更轻、扩散更快。物态变化属于物理变化：粒子本身没有改变，改变的只是排列方式与能量。
NH₃(g) + HCl(g) → NH₄Cl(s)
2. Atomic Structure | 原子结构
Atoms contain protons, neutrons and electrons. The atomic number is the proton number; the mass number is protons plus neutrons. Isotopes have the same proton number but different neutron numbers, which is why they have identical chemical properties but slightly different physical ones.
原子含质子、中子和电子。原子序数是质子数；质量数是质子数加中子数。同位素质子数相同但中子数不同，因此它们的化学性质完全相同，物理性质则略有差异。
Electrons occupy shells: 2, 8, 8 for the first three shells. Chemical behaviour depends on outer-shell electrons, so elements in the same group react in similar ways. An atom with a full outer shell, such as a noble gas, is unreactive.
电子排布：前三个电子层可容纳 2、8、8 个电子。化学性质取决于最外层电子，因此同族元素的反应方式相似。最外层为满壳层的原子（如稀有气体）很不活泼。
| Particle | Relative mass | Charge |
| Proton 质子 | 1 | +1 |
| Neutron 中子 | 1 | 0 |
| Electron 电子 | 1/1836 | -1 |
Relative atomic mass is the weighted average of the masses of the isotopes. Chlorine, for example, is about 75% ³⁵Cl and 25% ³⁷Cl, giving a relative atomic mass of 35.5. You may be asked to calculate this from percentage abundances, so practise the arithmetic without a calculator.
相对原子质量是各同位素质量的加权平均值。例如氯约含 75% 的 ³⁵Cl 和 25% 的 ³⁷Cl，其相对原子质量为 35.5。考题可能要求根据丰度百分比计算该值，请练习不依赖计算器完成运算。
Ar = (35 × 75 + 37 × 25) ÷ 100 = 35.5
3. The Periodic Table | 元素周期表
Elements are arranged in order of increasing proton number. The group number equals the number of outer-shell electrons, and the period number equals the number of occupied shells. This is why the table is such a powerful predictive tool: position tells you structure, and structure tells you reactivity.
元素按质子数递增排列。族序数等于最外层电子数，周期序数等于占用的电子层数。这正是周期表如此强大的预测工具的原因：位置告诉你结构，结构告诉你反应性。
Group I metals (lithium, sodium, potassium) are soft, low-density and react vigorously with water to give a metal hydroxide and hydrogen. Reactivity increases down the group because the outer electron is further from the nucleus and lost more easily. Group VII halogens become less reactive down the group for the opposite reason.
第 I 族金属（锂、钠、钾）质软、密度小，与水剧烈反应生成金属氢氧化物和氢气。反应性沿族向下增强，因为最外层电子离核更远、更易失去。第 VII 族卤素则相反，反应性沿族向下减弱。
Group 0 noble gases have full outer shells, so they are inert and are used where a non-reactive atmosphere is needed, such as in filament lamps. A zig-zag line separates metals from non-metals; elements next to it, such as silicon, show intermediate behaviour and are called metalloids.
0 族稀有气体最外层为满壳层，因此惰性，被用于需要不活泼气氛的场合，例如白炽灯泡。一条折线分隔金属与非金属；紧临折线的元素如硅表现出中间性质，称为类金属。
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
4. Chemical Bonding | 化学键
Ionic bonding occurs between metals and non-metals: electrons are transferred from the metal to the non-metal, producing positive and negative ions held by strong electrostatic attraction. Sodium chloride is the standard example, with Na⁺ and Cl⁻ arranged in a giant lattice.
离子键发生在金属与非金属之间：电子从金属转移到非金属，生成正离子和负离子，由强静电引力相互束缚。氯化钠是标准例子，Na⁺ 与 Cl⁻ 排列成巨型晶格。
Covalent bonding occurs between non-metals: atoms share pairs of electrons to complete their outer shells. Simple molecules such as H₂, Cl₂, H₂O, CO₂ and CH₄ have weak forces between molecules, so they have low melting and boiling points and do not conduct electricity.
共价键发生在非金属之间：原子共用电子对以填满最外层。像 H₂、Cl₂、H₂O、CO₂ 和 CH₄ 这样的简单分子，分子间作用力弱，因此熔沸点低且不导电。
- Ionic compounds: high melting points, conduct when molten or dissolved, often soluble in water.
离子化合物：熔点高，熔融或溶解时导电，通常溶于水。 - Simple molecular substances: low melting points, do not conduct, often volatile.
简单分子物质：熔点低，不导电，常易挥发。 - Giant covalent structures (diamond, graphite, silicon dioxide): very high melting points; graphite conducts because of delocalised electrons.
巨型共价结构（金刚石、石墨、二氧化硅）：熔点极高；石墨因离域电子而导电。 - Metals: positive ions in a sea of delocalised electrons, which explains conduction and malleability.
金属：正离子处于离域电子"海洋"中，这解释了导电性与延展性。
When drawing dot-and-cross diagrams, show only outer-shell electrons, use different symbols for electrons from different atoms, and remember that ions must carry square brackets with the charge shown outside.
画点叉图时，只画最外层电子，来自不同原子的电子用不同符号表示，并记住离子要加方括号且电荷写在括号外。
5. Formulae, Equations and the Mole | 化学式、方程式与摩尔
Writing formulae and balancing equations is the basic literacy of chemistry. Balance by adjusting coefficients only, never by changing subscripts, and always include state symbols: (s), (l), (g) and (aq). A balanced equation must have the same number of each type of atom on both sides.
书写化学式和配平方程式是化学的基本功。配平只能调整系数，绝不能改下标，并且始终写出状态符号：(s)、(l)、(g)、(aq)。配平后的方程式两边每种原子的数目必须相等。
ee relationships you need most are amount from mass, amount from concentration and volume, and gas volume at room temperature and pressure.
摩尔是含 6.02 × 10²³ 个粒子的物质的量。最常用的三个关系式是：由质量求物质的量、由浓度与体积求物质的量、以及室温常压下的气体体积。
m ÷ M n = c × V 1 mol gas = 24 dm³ at r.t.p.
Worked example: what volume of oxygen is needed to burn 12 g of magnesium completely? .25 mol of oxygen is required. At room temperature and pressure this is 0.25 × 24 = 6 dm³.
示例：完全燃烧 12 g 镁需要多少体积的氧气？先求镁的物质的量：n = 12 ÷ 24 = 0.5 mol。由 2Mg + O₂ → 2MgO 可知 Mg : O₂ 为 2 : 1，故需要 0.25 mol 氧气。室温常压下体积为 0.25 × 24 = 6 dm³。
Percentage yield compares the actual mass obtained with the theoretical maximum, and is always less than 100% because of incomplete reactions, side reactions and loss during transfer. Atom economy compares the mass of the desired product with the total mass of all products, and is a key idea in green chemistry.
产率把实际得到的质量与理论最大值相比较，由于反应不完全、副反应和转移损失，产率总是低于 100%。原子经济性则把目标产物的质量与所有产物的总质量相比较，是绿色化学的核心概念。
6. Acids, Bases and Salts | 酸碱盐
An acid releases hydrogen ions, H⁺, in aqueous solution; a base accepts them. An alkali is a soluble base. The pH scale runs from 0 to 14, with values below 7 acidic and above 7 alkaline. Universal indicator, litmus, methyl orange and phenolphthalein are the indicators you should be able to name and describe.
酸在水溶液中释放氢离子 H⁺；碱接受氢离子。可溶性碱称为碱液。pH 范围为 0 至 14，低于 7 为酸性，高于 7 为碱性。应能说出并描述通用指示剂、石蕊、甲基橙和酚酞的变色情况。
Strong acids such as hydrochloric and sulfuric acid ionise completely, while weak acids such as ethanoic acid ionise only partially, which is why they react more slowly and have higher pH at the same concentration. Diluting an acid raises the pH towards 7; diluting an alkali lowers it towards 7.
盐酸、硫酸等强酸完全电离，而乙酸等弱酸只部分电离，因此在相同浓度下反应更慢、pH 更高。稀释酸会使 pH 向 7 靠近；稀释碱则使 pH 向 7 降低。
- Acid + metal → salt + hydrogen.
酸 + 金属 → 盐 + 氢气。 - Acid + base → salt + water (neutralisation).
酸 + 碱 → 盐 + 水（中和反应）。 - Acid + carbonate → salt + water + carbon dioxide.
酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。 - Acid + metal oxide → salt + water.
酸 + 金属氧化物 → 盐 + 水。
Oxides can be classified as acidic (CO₂, SO₂), basic (CuO, MgO), amphoteric (ZnO, Al₂O₃) or neutral (CO, H₂O). To prepare a soluble salt, add excess solid metal, insoluble base or carbonate to the acid, filter off the excess, then evaporate and crystallise. Insoluble salts are made by precipitation, for example silver nitrate with sodium chloride.
氧化物可分为酸性（CO₂、SO₂）、碱性（CuO、MgO）、两性（ZnO、Al₂O₃）和中性（CO、H₂O）。制备可溶性盐时，向酸中加入过量的金属、不溶性碱或碳酸盐，过滤除去过量固体，再蒸发结晶。不溶性盐则通过沉淀反应制取，例如硝酸银与氯化钠。
AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
7. Chemical Energetics | 化学反应能量
Exothermic reactions release energy to the surroundings and cause a temperature rise; ΔH is negative. Combustion, neutralisation and respiration are typical examples. Endothermic reactions absorb energy and cause a temperature fall; ΔH is positive. Thermal decomposition is the standard example.
放热反应向环境释放能量，使温度上升，ΔH 为负值。燃烧、中和和呼吸作用是典型例子。吸热反应吸收能量，使温度下降，ΔH 为正值，热分解是标准例子。
The explanation lies in bond energies. Breaking bonds requires energy, while forming bonds releases energy. If the energy released when new bonds form is greater than the energy absorbed in breaking old bonds, the reaction is exothermic overall.
原因在于键能。断键需要吸能，成键则放能。如果形成新键释放的能量大于断开旧键吸收的能量，则整体为放热反应。
On an energy level diagram, the reactants are drawn on the left and the products on the right. A reaction profile also shows the activation energy, the minimum energy colliding particles must have for a successful reaction. A catalyst lowers this barrier without changing the overall energy change.
在能量图中，反应物画在左侧，产物画在右侧。反应能量曲线还要标出活化能，即碰撞粒子发生有效反应所需的最低能量。催化剂能降低这一能垒，但不改变总能量变化。
ΔH = energy in (bond breaking) − energy out (bond forming)
8. Rates of Reaction | 反应速率
The rate of a reaction depends on how often particles collide with enough energy. Four factors change it: concentration, temperature, surface area and the presence of a catalyst. Increasing any of the first three increases the frequency or the energy of collisions, so the rate rises.
反应速率取决于粒子以足够能量碰撞的频率。四个因素会改变速率：浓度、温度、表面积以及是否有催化剂。前三者中任意一个增大，都会提高碰撞频率或碰撞能量，因而速率上升。
Collision theory explains why powdered calcium carbonate reacts faster with acid than the same mass of large chips: the powder exposes a far greater surface area. It also explains why raising the temperature by 10 °C can roughly double the rate, since more particles exceed the activation energy.
碰撞理论解释了为何粉末状碳酸钙比同质量的大块与酸反应更快：粉末暴露的表面积大得多。它同样解释了为何升温 10 °C 可使速率大约翻倍，因为更多粒子超过了活化能。
- Measure gas volume with a syringe or inverted measuring cylinder.
用注射器或倒置量筒测量气体体积。 - Measure mass loss on a balance when a gas escapes.
当有气体逸出时，用天平测量质量损失。 - Time how long a cross becomes invisible through a cloudy solution.
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