📚 GCSE CIE Chemistry: Last-Minute Revision Notes | GCSE CIE 化学：考前冲刺笔记
This set of last-minute revision notes covers essential topics for the CIE IGCSE Chemistry (0620/0971) examination. Focus on key definitions, equations and testing procedures to boost your confidence before the exam. Every main idea is presented in English followed by Chinese to strengthen bilingual recall.
这本考前冲刺笔记涵盖了 CIE IGCSE 化学 (0620/0971) 考试的核心主题。重点关注关键定义、方程式和检验方法，帮助你在考前增强信心。每个重要知识点均以英文在先、中文在后的配对形式呈现，强化双语记忆。
1. Atomic Structure and the Periodic Table | 原子结构与周期表
All matter is made of atoms, each consisting of a tiny nucleus containing protons and neutrons, surrounded by electrons in shells. Protons carry a positive charge, electrons are negative, and neutrons have no charge.
所有物质都由原子组成，每个原子有一个微小的原子核（包含质子和中子），核外有分层排布的电子。质子带正电，电子带负电，中子不带电。
The atomic number (Z) equals the number of protons and defines the element. The mass number (A) is the total number of protons plus neutrons. Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, e.g., ¹²C and ¹⁴C.
原子序数 (Z) 等于质子数，决定了元素的种类。质量数 (A) 是质子数与中子数之和。同位素是具有相同质子数但中子数不同的同种元素原子，例如 ¹²C 和 ¹⁴C。
Electrons are arranged in shells: 2,8,8,2 for calcium (Ca). Elements in the same group of the periodic table have the same number of outer electrons and similar chemical properties. Group I (alkali metals) are soft, reactive metals that form 1⁺ ions; their reactivity increases down the group.
电子分层排布，如钙 (Ca) 的电子排布为 2,8,8,2。周期表中同一族的元素具有相同的最外层电子数和相似的化学性质。第 I 族（碱金属）是质软、反应性强的金属，形成 1⁺ 离子；反应活性向下递增。
Group VII (halogens) are diatomic non‑metals that form 1⁻ ions; reactivity decreases down the group. Group 0 (noble gases) are monatomic and unreactive because they have a full outer shell. Transition metals form coloured compounds and can have variable oxidation states.
第 VII 族（卤素）是双原子非金属，形成 1⁻ 离子；反应活性向下递减。第 0 族（稀有气体）为单原子分子，化学性质稳定，因为最外层电子已满。过渡金属可形成有色化合物并具有可变的氧化态。
2. Chemical Bonding and Structure | 化学键与结构
Ionic bonding occurs between a metal and a non‑metal by the transfer of electrons, forming a giant ionic lattice with strong electrostatic attractions. These compounds have high melting points and conduct electricity only when molten or dissolved in water because the ions are free to move.
离子键由金属和非金属通过电子转移形成，形成具有强静电吸引的巨型离子晶格。这类化合物熔点高，仅在熔融或溶于水时导电，因为此时离子可以自由移动。
Covalent bonding forms between non‑metals by sharing electron pairs. Simple molecular substances (e.g., H₂O, CO₂) have weak intermolecular forces, giving them low melting and boiling points. Giant covalent structures (diamond, graphite, SiO₂) have very high melting points because many strong covalent bonds must be broken throughout the structure.
共价键由非金属之间通过共用电子对形成。简单分子物质（如 H₂O、CO₂）分子间作用力弱，熔点和沸点低。巨型共价结构（金刚石、石墨、SiO₂）由于整个结构含有大量强共价键，熔点非常高。
In diamond each carbon atom forms four bonds in a tetrahedral arrangement, making it extremely hard and an electrical insulator. Graphite has layers of hexagonally arranged carbon atoms; each atom uses three bonds, leaving one delocalised electron per carbon, allowing graphite to conduct electricity and act as a lubricant.
金刚石中每个碳原子形成四个共价键，呈四面体排布，因此极硬且不导电。石墨具有六边形层状结构，每个碳原子形成三个共价键，剩余一个离域电子，使石墨能导电并可用作润滑剂。
Metallic bonding consists of a lattice of positive ions surrounded by a sea of delocalised electrons. This explains why metals are malleable, ductile and good conductors of heat and electricity.
金属键由沉浸在离域电子“海洋”中的阳离子晶格构成，解释了金属具有延展性、可锻性以及优良的导热和导电性。
3. Stoichiometry and the Mole Concept | 化学计量学与摩尔概念
The relative atomic mass (Aᵣ) is the average mass of an atom compared to 1/12 of the mass of a ¹²C atom. The relative molecular mass (Mᵣ) is the sum of the Aᵣ values of all atoms in a molecule.
相对原子质量 (Aᵣ) 是原子的平均质量与一个 ¹²C 原子质量的 1/12 相比的比值。相对分子质量 (Mᵣ) 是分子中所有原子的 Aᵣ 之和。
n = m / Mᵣ
The mole is the amount of substance that contains 6.02 × 10²³ particles (Avogadro constant). Use the equation n = mass / Mᵣ to find moles from mass.
摩尔是含有 6.02 × 10²³ 个微粒（阿伏伽德罗常数）的物质的量。利用公式 n = 质量 / Mᵣ 可从质量求摩尔数。
n = V (dm³) / 24
At room temperature and pressure (r.t.p.), one mole of any gas occupies 24 dm³. For solutions, moles = concentration (mol/dm³) × volume (dm³).
在常温常压 (r.t.p.) 下，1 摩尔任何气体的体积为 24 dm³。对于溶液，摩尔数 = 浓度 (mol/dm³) × 体积 (dm³)。
The empirical formula shows the simplest whole‑number ratio of atoms in a compound. To find it, convert masses (or percentages) to moles, then divide by the smallest mole value.
实验式（最简式）表示化合物中原子个数的最简单整数比。求实验式时，先将质量（或百分比）换算成摩尔，再除以最小摩尔数。
Percentage yield = (actual yield / theoretical yield) × 100. Percentage purity = (mass of pure substance / total mass of sample) × 100.
产率 = (实际产量 / 理论产量) × 100%。纯度 = (纯净物质量 / 样品总质量) × 100%。
4. Electrolysis | 电解
Electrolysis uses direct current to break down ionic compounds. The electrolyte is the molten or aqueous ionic substance. The positive electrode is the anode (attracts anions), and the negative electrode is the cathode (attracts cations).
电解利用直流电分解离子化合物。电解质是熔融或水溶液状态的离子化合物。正极为阳极（吸引阴离子），负极为阴极（吸引阳离子）。
In the electrolysis of molten lead(II) bromide (PbBr₂): at the cathode, Pb²⁺ gains electrons → Pb (grey liquid); at the anode, Br⁻ loses electrons → Br₂ (red‑brown gas).
电解熔融溴化铅 (PbBr₂)：阴极上 Pb²⁺ 得电子 → Pb（灰色液体）；阳极上 Br⁻ 失电子 → Br₂（红棕色气体）。
For aqueous solutions, the products depend on the reactivity of the ions. At the cathode, the less reactive cation (usually H⁺ from water or a metal ion below hydrogen in the reactivity series) is discharged. At the anode, the simplest halide ion is discharged if present, otherwise OH⁻ from water gives oxygen.
对于水溶液，产物取决于离子的反应活性。阴极上，较不活泼的阳离子（通常是来自水的 H⁺ 或活动性在氢之后的金属离子）优先放电。阳极上，如果存在卤离子则优先放电，否则来自水的 OH⁻ 放电产生氧气。
Electrolysis of concentrated aqueous NaCl: cathode produces H₂ gas, anode produces Cl₂ gas, leaving NaOH in solution. Copper purification uses an impure copper anode and a pure copper cathode in CuSO₄ solution; at the anode Cu dissolves, at the cathode pure Cu deposits.
电解浓氯化钠水溶液：阴极产生 H₂，阳极产生 Cl₂，溶液中留下 NaOH。精炼铜时，以不纯铜为阳极，纯铜为阴极，在 CuSO₄ 溶液中进行；阳极铜溶解，阴极上沉积纯铜。
5. Energy Changes in Reactions | 反应中的能量变化
Exothermic reactions release energy to the surroundings (e.g., combustion, neutralisation). Endothermic reactions absorb energy (e.g., photosynthesis, thermal decomposition).
放热反应向环境释放能量（如燃烧、中和反应）。吸热反应从环境吸收能量（如光合作用、热分解反应）。
ΔH = Σ (bond energies of bonds broken) – Σ (bond energies of bonds formed)
Use bond energies to calculate enthalpy change. Bond breaking is endothermic, bond making is exothermic.
利用键能计算焓变。断裂化学键需要吸热，形成化学键会放热。
Energy profile diagrams show the energy change during a reaction. Exothermic profiles go down overall, endothermic profiles go up. The activation energy (Eₐ) is the minimum energy needed for a reaction to occur.
能级图展示反应过程中的能量变化。放热反应总体能量下降，吸热反应上升。活化能 (Eₐ) 是引发反应所需的最小能量。
In a hydrogen‑oxygen fuel cell: 2H₂ + O₂ → 2H₂O, producing electrical energy. The overall reaction is exothermic, and the only waste product is water.
氢氧燃料电池中：2H₂ + O₂ → 2H₂O，产生电能。总反应为放热反应，唯一的废弃物是水。
6. Acids, Bases and Salts | 酸、碱和盐
An acid is a proton (H⁺) donor; a base is a proton acceptor. Alkalis are soluble bases that release OH⁻ ions in water. The pH scale runs from 0 (strongly acidic) to 14 (strongly alkaline). Universal indicator turns through a colour range: red (acid), green (neutral), purple (alkali).
酸是质子 (H⁺) 的给予体；碱是质子接受体。可溶性碱在水溶液中释放 OH⁻ 离子，称为碱液。pH 标度范围 0（强酸性）到 14（强碱性）。通用指示剂颜色变化为：红（酸）、绿（中性）、紫（碱）。
Acid + metal → salt + hydrogen gas. Acid + base (or alkali) → salt + water. Acid + carbonate → salt + water + carbon dioxide.
酸 + 金属 → 盐 + 氢气。酸 + 碱（或碱液）→ 盐 + 水。酸 + 碳酸盐 → 盐 + 水 + 二氧化碳。
Soluble salts are prepared by titration (for alkali + acid) or by adding excess insoluble base/metal/carbonate to acid, then filtering and crystallising. Insoluble salts are made by precipitation: mix two solutions containing the required ions, filter and wash the precipitate.
可溶性盐的制备可通过滴定法（碱液与酸）或将过量的不溶性碱/金属/碳酸盐加入酸中，然后过滤、结晶。难溶性盐通过沉淀法制备：将含有目标离子的两种溶液混合，过滤、洗涤沉淀。
Gas tests: H₂ burns with a squeaky pop; O₂ relights a glowing splint; CO₂ turns limewater milky; Cl₂ bleaches damp blue litmus paper; NH₃ turns damp red litmus paper blue.
气体检验：H₂ 燃烧发出爆鸣声；O₂ 使带火星的木条复燃；CO₂ 使石灰水变浑浊；Cl₂ 使湿润的蓝色石蕊试纸褪色；NH₃ 使湿润的红色石蕊试纸变蓝。
7. The Reactivity Series and Redox | 金属活动性顺序与氧化还原
The reactivity series of metals, from most to least reactive: K, Na, Ca, Mg, Al, (C), Zn, Fe, (H), Cu, Ag, Au. A more reactive metal can displace a less reactive metal from its compound (e.g., Zn + CuSO₄ → ZnSO₄ + Cu).
金属活动性顺序由强到弱：K、Na、Ca、Mg、Al、(C)、Zn、Fe、(H)、Cu、Ag、Au。较活泼的金属能将较不活泼的金属从其化合物中置换出来（如 Zn + CuSO₄ → ZnSO₄ + Cu）。
Redox reactions involve both oxidation and reduction. Remember OIL RIG: Oxidation Is Loss of electrons, Reduction Is Gain of electrons. A reducing agent donates electrons, an oxidising agent accepts electrons.
氧化还原反应同时包含氧化和还原。记住 OIL RIG：氧化是失电子，还原是得电子。还原剂提供电子，氧化剂接受电子。
Rusting of iron requires both oxygen and water
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