📚 IGCSE AQA Chemistry: Last-Minute Revision Notes | IGCSE AQA 化学：考前冲刺笔记
These last-minute revision notes condense the entire IGCSE AQA Chemistry specification into clear, essential points. Focus on key definitions, calculations, reactions and common exam traps to quickly refresh your memory before the final test.
这份考前冲刺笔记将 IGCSE AQA 化学整个考纲浓缩为清晰的核心要点。集中精力掌握关键定义、计算、反应以及常见考试陷阱，在最终考试前快速唤醒你的记忆。
1. Atomic Structure and Periodic Table | 原子结构与周期表
Atoms contain a tiny, dense nucleus of protons and neutrons, surrounded by electrons moving in shells. Proton number defines the element, while the sum of protons and neutrons gives the mass number.
原子包含一个由质子和中子构成的微小致密原子核，核外电子分层排布。质子数决定元素种类，质子数加中子数等于质量数。
Subatomic particles:
| Particle | Relative charge | Relative mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1836 |
亚原子粒子：质子带+1电荷，相对质量1；中子不带电，相对质量1；电子带-1电荷，相对质量极小。
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. For example, carbon-12 (¹²C) has 6 protons and 6 neutrons, while carbon-14 (¹⁴C) has 6 protons and 8 neutrons. They share identical chemical properties because electrons remain unchanged.
同位素是指质子数相同而中子数不同的同种原子。例如碳-12 (¹²C) 含6个质子和6个中子，碳-14 (¹⁴C) 含6个质子和8个中子。由于电子排布相同，它们的化学性质几乎一致。
Electrons fill shells following the 2,8,8 rule up to calcium. The group number equals the number of outer-shell electrons for Groups 1–2 and 13–18. The period number indicates how many shells are occupied. Elements in the same group have similar reactivity.
电子按2,8,8规则排列 (到钙为止)。主族元素的族数等于最外层电子数 (第1–2族和13–18族)。周期数代表已占据的电子层数。同族元素化学性质相似。
2. Chemical Bonding and Structure | 化学键与结构
Ionic bonding occurs between metals and non‑metals by transferring electrons, forming oppositely charged ions held in a giant lattice. The formula of an ionic compound gives the simplest ratio, e.g. NaCl, MgO, CaCl₂. The strong electrostatic forces result in high melting points and electrical conductivity only when molten or dissolved.
离子键存在于金属与非金属之间，通过电子转移形成阴、阳离子，并构成巨大离子晶格。化学式表示最简整数比，如 NaCl、MgO、CaCl₂。强大的静电引力使离子化合物熔点高，只 有在熔融或溶于水时才能导电。
Covalent bonding involves sharing pairs of electrons between non‑metal atoms. Simple molecular substances like H₂O, CO₂ and CH₄ have low melting points because only weak intermolecular forces need to be overcome, even though the covalent bonds inside molecules are strong.
共价键通过非金属原子间共用电子对形成。像 H₂O、CO₂、CH₄ 这样的简单分子物质熔点较低，因为只需克服微弱的分子间作用力，尽管分子内的共价键很强。
Giant covalent structures (diamond, graphite, silicon dioxide) have millions of strong covalent bonds throughout the lattice, giving them extremely high melting points. Diamond is hard because each carbon bonds to four others; graphite is soft and conducts electricity due to delocalised electrons between layers.
巨型共价结构 (金刚石、石墨、二氧化硅) 在整个晶格中拥有不计其数的强共价键，因此熔点极高。金刚石很硬，因为每个碳原子与另外四个碳原子成键；石墨较软且在层间有离域电子，可导电。
Metallic bonding consists of a regular lattice of positive metal ions surrounded by a sea of delocalised electrons. This allows metals to conduct heat and electricity, and to be bent (malleable) without breaking because the layers can slide past each other.
金属键由规则排列的金属阳离子和包围它们的离域电子“海洋”构成，这使得金属能导热、导电，也可以在受力时层与层之间滑动，从而具有延展性而不断裂。
3. Quantitative Chemistry | 定量化学
The relative atomic mass (Aᵣ) is the weighted average mass of an element’s isotopes on a scale where ¹²C = 12. Relative formula mass (Mᵣ) is the sum of Aᵣ values in a formula unit. One mole of a substance contains 6.02 × 10²³ particles and has a mass in grams equal to its Mᵣ.
相对原子质量 (Aᵣ) 是元素同位素的加权平均质量，基准为 ¹²C = 12。相对式量 (Mᵣ) 是化学式中各 Aᵣ 之和。1 摩尔物质含 6.02 × 10²³ 个微粒，其质量以克为单位时数值 等同于 Mᵣ。
moles = mass (g) / Mᵣ (g/mol)
摩尔数 = 质量 (g) / 摩尔质量 (g/mol)
Concentration in mol/dm³ is calculated by moles of solute divided by volume in dm³. If the volume is given in cm³, divide by 1000 first. Gas volumes at room temperature and pressure: one mole of any gas occupies 24 dm³.
浓度 (mol/dm³) 由溶质摩尔数除以溶液体积 (dm³) 得到。若体积以 cm³ 给出，需先除以 1000。常温常压下，1 摩尔任何气体体积约为 24 dm³。
volume of gas (dm³) = moles × 24
气体体积 (dm³) = 摩尔数 × 24
Empirical formula is the simplest whole‑number ratio of atoms; molecular formula shows the actual number. Percentage yield = (actual yield / theoretical yield) × 100. Atom economy = (Mᵣ of desired product / sum of Mᵣ of all reactants) × 100.
经验式是各原子最简整数比；分子式则给出实际原子个数。产率 = (实际产量 / 理论产量) × 100。原子经济性 = (目标产物 Mᵣ / 所有反应物 Mᵣ 总和) × 100。
4. Chemical Energetics | 化学能量学
Exothermic reactions transfer thermal energy to the surroundings, causing a temperature rise (e.g. combustion, neutralisation). Endothermic reactions absorb energy from the surroundings, causing cooling (e.g. photosynthesis, thermal decomposition).
放热反应向环境释放热能，导致温度升高 (如燃烧、中和)。吸热反应从环境吸收能量，导致温度下降 (如光合作用、热分解)。
Reaction profiles show energy changes. The activation energy (Eₐ) is the minimum collision energy needed. In an exothermic profile, products have lower energy than reactants; in an endothermic profile, products have higher energy.
反应剖面图展示能量变化。活化能 (Eₐ) 是发生有效碰撞所需的最低能量。放热反应中产物总能量低于反应物；吸热反应中产物总能量高于反应物。
Bond energy calculations: ΔH = sum of energy absorbed to break bonds – sum of energy released when making bonds. A negative ΔH means the reaction is exothermic overall.
键能计算：ΔH = 断裂化学键吸收的总能量 – 形成化学键释放的总能量。若 ΔH 为负值，反应整体放热。
5. Rates of Reaction | 反应速率
Rate is how quickly reactants are used up or products are made. It can be measured by recording change in mass, gas volume or turbidity over time. For a graph of product volume vs time, the steeper the slope, the faster the rate.
反应速率指反应物消耗或产物生成的快慢。可通过记录质量变化、气体体积变化或浊度随时间的变化来测量。产物体积–时间图中，斜率越大，反应越快。
Collision theory: particles must collide with sufficient energy (≥ Eₐ) and with the correct orientation. Increasing temperature gives particles more kinetic energy, so a greater proportion of collisions exceed Eₐ. Increasing concentration or pressure increases the frequency of collisions.
碰撞理论：粒子必须以足够的能量 (≥ 活化能) 和合适的取向碰撞。升温使粒子动能增大，因此超过活化能的碰撞比例上升。增大浓度或压强可提高碰撞频率。
Catalysts provide an alternative pathway with lower activation energy, speeding up both forward and backward reactions equally. They are not used up. Enzymes are biological catalysts.
催化剂提供一条活化能较低的反应路径，同等程度地加快正、逆反应速率，本身不被消耗。酶是生物催化剂。
6. Reversible Reactions and Equilibrium | 可逆反应与平衡
A reversible reaction is shown by the symbol ⇌. At equilibrium in a closed system, the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant but not necessarily equal.
可逆反应用符号 ⇌ 表示。在密闭体系中达到平衡时，正、逆反应速率相等，各物质浓度不再改变，但不一定相等。
Dynamic equilibrium: rate forward = rate reverse
动态平衡：正反应速率 = 逆反应速率
Le Chatelier’s principle: if a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts to counteract the change. Increasing temperature favours the endothermic direction; increasing pressure favours the side with fewer gas molecules; increasing concentration of a reactant shifts equilibrium to make more product.
勒夏特列原理：如果改变影响平衡的条件，平衡会向减弱这种改变的方向移动。升温向吸热方向移动；加压向气体分子总数较少的方向移动；增加反应物浓度会使平衡向生成物方向移动。
Haber process for NH₃: N₂ + 3H₂ ⇌ 2NH₃, exothermic. Conditions: 450 °C, 200 atm, iron catalyst. A compromise temperature is used to balance yield and rate.
哈伯法合成氨：N₂ + 3H₂ ⇌ 2NH₃，放热。条件：450 °C、200 atm、铁催化剂。工业上采用折中温度，以兼顾产率和速率。
7. Acids, Bases and Salts | 酸、碱和盐
Acids are proton (H⁺) donors; alkalis are soluble bases that release OH⁻ ions. The pH scale runs from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral. pH can be measured with universal indicator or a pH meter.
酸是质子 (H⁺) 的给予体；碱是可溶性的能释放 OH⁻ 的物质。pH 范围 0 (强酸性) 到 14 (强碱性)，7 为中性。pH 可用通用指示剂或 pH 计测量。
Neutralisation: H⁺(aq) + OH⁻(aq) → H₂O(l)
中和反应：H⁺(aq) + OH⁻(aq) → H₂O(l)
Making soluble salts: acid + metal → salt + hydrogen; acid + metal oxide → salt + water; acid + metal carbonate → salt + water + CO₂. Crystals are obtained by filtration and evaporation/crystallisation.
可溶性盐的制备：酸 + 金属 → 盐 + 氢气；酸 + 金属氧化物 → 盐 + 水；酸 + 金属碳酸盐 → 盐 + 水 + 二氧化碳。通过过滤和蒸发/结晶可获得晶体。
Titration allows accurate determination of unknown concentrations using a standard solution and a suitable indicator. Repeat until concordant titres are obtained (within 0.1 cm³). Burette readings are always recorded to two decimal places.
滴定法利用标准溶液和适当指示剂准确测定未知浓度。需重复操作直到获得符合平行要求的滴定数据 (相差不超过 0.1 cm³)。滴定管读数必须记录至小数点后两位。
8. Electrolysis | 电解
Electrolysis splits an ionic compound into its elements using direct current. The electrolyte is the molten or aqueous ionic compound. Cations (positive) migrate to the cathode (negative electrode) and gain electrons (reduction). Anions (negative) migrate to the anode (positive electrode) and lose electrons (oxidation).
电解是利用直流电分解离子化合物的过程。电解质是熔融或溶液状态的离子化合物。阳离子向阴极 (负极) 移动，获得电子 (还原)；阴离子向阳极 (正极) 移动，失去电子 (氧化)。
In molten electrolysis, metal is produced at the cathode and non‑metal at the anode. For aluminium extraction: Al³⁺ + 3e⁻ → Al (cathode); 2O²⁻ → O₂ + 4e⁻ (anode). Cryolite is added to lower the melting point of Al₂O₃.
熔融电解时，阴极生成金属，阳极生成非金属。铝的冶炼：阴极 Al³⁺ + 3e⁻ → Al；阳极 2O²⁻ → O₂ + 4e⁻。加入冰晶石可降低氧化铝的熔点。
In aqueous electrolysis, the products depend on relative reactivity and concentration. At the cathode, if the metal is less reactive than hydrogen, the metal is deposited; otherwise hydrogen gas forms. At the anode, halide ions (if present) are discharged in preference to OH⁻, giving Cl₂ or Br₂; otherwise oxygen is produced.
在水溶液电解中，产物取决于离子的相对活泼性及浓度。阴极：若金属比氢不活泼，金属析出；否则放出氢气。阳极：卤离子 (若存在) 优先于 OH⁻ 放电，生成 Cl₂ 或 Br₂；否则产生氧气。
9. Organic Chemistry | 有机化学
Hydrocarbons contain only carbon and hydrogen. Alkanes (CₙH₂ₙ₊₂, e.g. CH₄) have single bonds and are saturated; alkenes (CₙH₂ₙ, e.g. C₂H₄) contain a C=C double bond and are unsaturated. The functional group determines characteristic reactions.
烃只含碳和氢。烷烃 (通式 CₙH₂ₙ₊₂，如 CH₄) 只有单键，是饱和烃；烯烃 (通式 CₙH₂ₙ，如 C₂H₄) 含有 C=C 双键，是不饱和烃。官能团决定了物质的特征反应。
Alkenes decolourise bromine water by addition across the double bond; this is a test for unsaturation. Addition polymerisation: many monomer molecules (e.g. ethene) join to form a long chain with no other products.
烯烃能使溴水褪色，因为发生了双键上的加成反应；这用于检验不饱和键。加聚反应：许多单体分子 (如乙烯) 连接成长链，无其他副产物。
Alcohols contain the –OH group (e.g. ethanol C₂H₅OH). They burn, can be oxidised to carboxylic acids, and react with sodium. Carboxylic acids (–COOH) are weak acids; they react with alcohols to form esters with a fruity smell.
醇含有 –OH 羟基 (如乙醇 C₂H₅OH)。醇能燃烧，可被氧化成羧酸，也能与钠反应。羧酸 (–COOH) 是弱酸；它们与醇反应生成具有果香味的酯。
10. Chemical Analysis | 化学分析
Gas tests: oxygen relights a glowing splint; hydrogen gives a squeaky pop with a lit splint; carbon dioxide turns limewater milky; chlorine bleaches damp litmus paper.
气体检验：氧气使带火星木条复燃；氢气点燃有爆鸣声；二氧化碳使石灰水变浑浊；氯气使湿润的石蕊试纸漂白。
Flame tests identify metal ions: lithium (crimson), sodium (yellow), potassium (lilac), calcium (orange‑red), copper (green). Sodium hydroxide precipitation can confirm Cu²⁺ (blue), Fe²⁺ (green), Fe³⁺ (brown), Al³⁺ (white, dissolves in excess NaOH) and Ca²⁺ / Mg²⁺ (white).
焰色反应可检验金属离子：锂 (深红)、钠 (黄)、钾 (淡紫)、钙 (橙红)、铜 (绿)。用氢氧化钠溶液产生沉淀可鉴定：Cu²⁺ (蓝色)、Fe²⁺ (绿色)、Fe³⁺ (红褐色)、Al³⁺ (白色，溶于过量 NaOH)、Ca²⁺ / Mg²⁺ (白色)。
Anion tests: carbonate (+ acid → CO₂); sulfate (+ HCl, then BaCl₂ → white BaSO₄); halides (+ HNO₃, then AgNO₃ → AgCl white, AgBr cream, AgI yellow).
阴离子检验：碳酸根 (加酸产生 CO₂)；硫酸根 (加盐酸和 BaCl₂ 产生白色 BaSO₄)；卤离子 (加稀硝酸和 AgNO₃ 产生 AgCl 白色、AgBr 奶油色、AgI 黄色)。
Chromatography separates mixtures based on differences in solubility. Rf = distance moved by spot / distance moved by solvent front. Pure substances give a single spot.
色谱法利用溶解度的差异分离混合物。比移值 Rf = 斑点移动距离 / 溶剂前沿移动距离。纯物质只显示一个斑点。
11. Chemistry of the Atmosphere | 大气化学
Today’s atmosphere is about 78 % N₂, 21 % O₂, 0.9 % Ar and 0.04 % CO₂. Photosynthesis by early algae and plants reduced CO₂ and increased O₂ over billions of years. Oceans formed, absorbing CO₂ and forming carbonate rocks.
现今大气大致含 78 % N₂、21 % O₂、0.9 % Ar 和 0.04 % CO₂。早期藻类和植物的光合作用在数十亿年间降低了 CO₂ 浓度，提升了 O₂ 含量。海洋形成并吸收 CO₂，产生碳酸盐岩石。
The greenhouse effect: CO₂, methane and water vapour absorb infrared radiation emitted by Earth, trapping heat. Human activities (burning fossil fuels, deforestation, agriculture) increase greenhouse gas levels, leading to global warming and climate change.
温室效应：CO₂、甲烷和水蒸气吸收地表发出的红外辐射，将热量截留。人类活动 (燃烧化石燃料、砍伐森林、农业) 使温室气体浓度上升，导致全球变暖与气候变化。
Combustion of fuels can produce pollutants: incomplete combustion gives CO (toxic) and soot; sulfur impurities produce SO₂ (acid rain); high temperatures in engines form NOₓ, which also causes acid rain and respiratory problems.
燃料燃烧会产生污染物：不完全燃烧生成有毒的 CO 和炭黑；含硫杂质生成 SO₂ (导致酸雨)；发动机高温生成氮氧化物 NOₓ，同样引发酸雨和呼吸道疾病。
12. Exam Techniques & Common Pitfalls | 考试技巧与常见陷阱
Always show your working in calculations; include units. Write balanced symbol equations when asked, and ensure state symbols (s), (l), (g), (aq) where required. Check that equations satisfy conservation of mass.
计算题务必写出计算过程并标注单位。按要求写出配平的化学方程式，并在需要时注明物质状态 (s)、(l)、(g)、(aq)。务必确认方程式符合质量守恒。
When describing trends, compare the extremes and mention what the trend shows. In ‘explain’ questions, use scientific terms like ‘activation energy’, ‘collision frequency’, ‘delocalised electrons’ – never just repeat the question.
描述变化趋势时，要对比两端并指出整体走向。在“解释”类问题中，使用科学术语如“活化能”、“碰撞频率”、“离域电子”——不要只重复题目中的话。
Watch out for confusion between intermolecular forces and covalent bonds in melting point explanations. For simple molecules, it is the weak intermolecular forces that are broken, not the strong covalent bonds.
解释熔点时注意区分分子间作用力和共价键。简单分子物质熔化时断裂的是微弱的分子间作用力，而非牢固的共价键。
In electrolysis, remember that OH⁻ is discharged at the anode only when halide ions are absent. In equilibrium questions, clearly state the shift of equilibrium and the resulting change in yield.
电解中，只有在不存在卤离子时，OH⁻ 才会在阳极放电。平衡问题中，要先明确指出平衡移动的方向，再说明产率如何变化。
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