📚 GCSE Chemistry: End-of-Term Revision Guide | GCSE 化学：期末复习提纲
This end-of-term revision guide provides a concise overview of the key topics covered in GCSE Chemistry. Use it to focus your revision on essential concepts, definitions, equations, and practical skills.
本期末复习提纲简要总结了GCSE化学涵盖的关键主题。用它来集中复习基本概念、定义、方程式和实验技能。
1. Atomic Structure and the Periodic Table | 原子结构与周期表
All matter is made of tiny particles called atoms. Each atom has a central nucleus containing protons and neutrons, with electrons moving around the nucleus in shells. The atomic number (Z) equals the number of protons and defines the element. The mass number (A) is the total number of protons and neutrons.
所有物质都由称为原子的微小粒子构成。每个原子有一个由质子和中子组成的中心原子核，电子在核外按壳层排布。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。
Isotopes are atoms of the same element with different numbers of neutrons. They have the same chemical properties but different physical properties (e.g. mass). The relative atomic mass (Ar) is the average mass of an element’s isotopes, weighted by their natural abundance.
同位素是质子数相同、中子数不同的同种原子。它们的化学性质相同但物理性质（如质量）不同。相对原子质量（Ar）是元素各同位素质量的加权平均值，由其天然丰度决定。
The periodic table arranges elements in order of increasing atomic number. Vertical columns are called groups; horizontal rows are called periods. Elements in the same group have the same number of electrons in their outer shell, which gives them similar chemical properties. Group 1 metals (the alkali metals) become more reactive as you go down the group, while Group 7 (the halogens) become less reactive down the group. Group 0 (the noble gases) are unreactive because they have full outer shells of electrons.
周期表按原子序数递增的顺序排列元素。纵列称为族，横行称为周期。同一族元素最外层电子数相同，因此化学性质相似。第1族金属（碱金属）从上到下反应性逐渐增强，而第7族（卤素）从上到下反应性逐渐减弱。第0族（稀有气体）因为最外层电子已满，性质稳定不易发生反应。
2. Bonding, Structure, and Properties | 化学键、结构与性质
Ionic bonding involves a transfer of electrons from a metal atom to a non-metal atom, forming oppositely charged ions that attract each other in a giant ionic lattice. Ionic compounds have high melting and boiling points and conduct electricity when molten or dissolved in water because their ions are free to move.
离子键是金属原子将电子转移给非金属原子，形成带相反电荷的离子，这些离子通过静电吸引力构成巨大的离子晶格。离子化合物熔点和沸点很高，在熔融或溶于水时可以导电，因为此时离子可以自由移动。
Covalent bonding occurs when non-metal atoms share pairs of electrons. Simple molecular substances like H₂O and CO₂ have strong covalent bonds inside the molecules but weak intermolecular forces between molecules, leading to low melting and boiling points. Giant covalent structures, such as diamond (each carbon atom bonded to four others) and graphite (layers of carbon atoms with free electrons), have very high melting points. Graphite conducts electricity because of delocalised electrons between the layers.
共价键是指非金属原子之间共享电子对。像H₂O和CO₂这类简单分子物质，分子内共价键很强，但分子间的分子间作用力很弱，因此熔点和沸点较低。巨分子共价结构如金刚石（每个碳原子与另外四个碳原子成键）和石墨（碳原子层状结构且存在自由电子）则具有很高的熔点。石墨因层间存在离域电子而能够导电。
Metallic bonding describes the attraction between positive metal ions and a sea of delocalised electrons. This structure gives metals the ability to conduct heat and electricity, and it allows metals to be bent and shaped (malleable and ductile). Alloys are mixtures of metals with other elements; their distorted layers make alloys harder than pure metals.
金属键是金属正离子与离域电子的“海洋”之间的吸引力。这种结构赋予金属传导热量和电流的能力，同时使金属具有延展性和可塑性。合金是金属与其他元素的混合物，其扭曲的原子层使得合金比纯金属更坚硬。
3. Quantitative Chemistry | 定量化学
The mole is the unit for amount of substance. One mole contains 6.02 × 10²³ particles (Avogadro’s constant). The mass of one mole of a substance is its relative formula mass (Mᵣ) in grams.
摩尔是物质的量的单位。1摩尔包含6.02 × 10²³个粒子（阿伏伽德罗常数）。1摩尔物质的质量就是以克为单位的相对化学式量（Mᵣ）。
Number of moles = mass (g) / Mᵣ (g/mol)
摩尔数 = 质量（克）/ 相对化学式量（克/摩尔）
The law of conservation of mass states that the total mass of reactants equals the total mass of products in a chemical reaction. Calculations often involve using balanced symbol equations to work out reacting masses. Concentration can be measured in g/dm³ or mol/dm³. Percentage yield and atom economy are important measures of reaction efficiency.
质量守恒定律指出，化学反应中反应物的总质量等于生成物的总质量。计算题常需利用配平的化学方程式来求出反应质量。浓度可用g/dm³或mol/dm³表示。产率和原子经济性是衡量反应效率的重要指标。
Percentage yield = (actual yield / theoretical yield) × 100
产率 =（实际产量 / 理论产量）× 100
4. Chemical Changes | 化学变化
Acids form H⁺ ions in water. Strong acids fully ionise, while weak acids only partially ionise. The pH scale measures the concentration of H⁺ ions: the lower the pH, the more acidic the solution. Bases neutralise acids to form a salt and water. Metal + acid → salt + hydrogen; metal oxide + acid → salt + water; metal carbonate + acid → salt + water + carbon dioxide.
酸在水中产生H⁺离子。强酸完全电离，弱酸仅部分电离。pH标度衡量H⁺离子浓度：pH越小，酸性越强。碱能中和酸生成盐和水。金属 + 酸 → 盐 + 氢气；金属氧化物 + 酸 → 盐 + 水；金属碳酸盐 + 酸 → 盐 + 水 + 二氧化碳。
The reactivity series ranks metals by how readily they form positive ions. More reactive metals can displace less reactive metals from their compounds. Reduction is gain of electrons; oxidation is loss of electrons (OIL RIG). Electrolysis uses electricity to break down ionic compounds. During electrolysis of molten salts, metals form at the cathode (-) and non-metals at the anode (+). In aqueous solutions, the products depend on the reactivity of the ions.
金属活动性顺序根据金属形成正离子的难易程度排序。活动性较强的金属可从化合物中置换出活动性较弱的金属。还原是得到电子，氧化是失去电子（OIL RIG）。电解是利用电流分解离子化合物的过程。电解熔融盐时，金属在阴极(-)生成，非金属在阳极(+)生成。在水溶液中，产物取决于离子的活动性。
5. Energy Changes | 能量变化
Exothermic reactions transfer energy to the surroundings (e.g. combustion, neutralisation). Endothermic reactions absorb energy from the surroundings (e.g. thermal decomposition). The energy change can be shown on a reaction profile diagram, where the overall energy change is the difference between the energy of reactants and products.
放热反应向周围环境释放能量（如燃烧、中和）。吸热反应从周围环境吸收能量（如热分解）。能量变化可用反应过程图表示，图中的总能量变化是反应物与生成物的能量差值。
Bond energy calculations can be used to find the energy change of a reaction: energy absorbed to break bonds minus energy released when new bonds form. A negative value indicates an exothermic reaction.
通过键能计算可得出反应的能量变化：断裂化学键吸收的能量减去形成新化学键释放的能量。若结果为负值，表示反应放热。
ΔH = Σ (bond energies of bonds broken) – Σ (bond energies of bonds formed)
反应焓变 = 反应物断键吸能之和 – 生成物成键释能之和
In a simple electric cell, two different metals in an electrolyte produce a voltage. Fuel cells, such as hydrogen-oxygen fuel cells, convert chemical energy directly into electrical energy and form only water as waste.
在简单的化学电池中，两种不同金属浸入电解液可产生电压。燃料电池，例如氢氧燃料电池，直接将化学能转化为电能，且唯一的排放物是水。
6. Rate and Extent of Chemical Change | 化学反应速率与平衡
The rate of a chemical reaction can be increased by raising the temperature, increasing the concentration of reactants in solution, increasing the pressure of gaseous reactants, increasing the surface area of solid reactants, or adding a catalyst. According to collision theory, particles must collide with sufficient energy (activation energy) and the correct orientation for a reaction to occur.
提高温度、增大溶液中反应物的浓度、增大气体反应物的压强、增大固体反应物的表面积或加入催化剂，都能加快反应速率。根据碰撞理论，粒子必须发生碰撞且具有足够的能量（活化能）和正确的取向，反应才会发生。
Many reactions are reversible. At equilibrium, the forward and backward rates are equal, and the concentrations of reactants and products remain constant. Changing the conditions can shift the equilibrium position. If temperature is increased, the equilibrium shifts in the endothermic direction; if pressure is increased, the equilibrium shifts to the side with fewer moles of gas. Catalysts do not affect the position of equilibrium, but they help the system reach equilibrium faster.
许多反应是可逆的。达到平衡时，正逆反应速率相等，反应物和生成物的浓度保持不变。改变条件可使平衡发生移动。升高温度，平衡向吸热方向移动；增大压强，平衡向气体摩尔数较少的方向移动。催化剂不影响平衡位置，但能加快达到平衡的速度。
7. Organic Chemistry | 有机化学
Crude oil is a mixture of hydrocarbons, mostly alkanes (CnH2n+2). Fractional distillation separates crude oil into fractions based on boiling point. Alkanes are saturated hydrocarbons with single C–C bonds. Alkenes (CnH2n) are unsaturated hydrocarbons with at least one C=C double bond; they turn bromine water colourless. Cracking breaks large alkane molecules into smaller, more useful alkanes and alkenes.
原油是碳氢化合物的混合物，主要成分为烷烃（CnH2n+2）。分馏根据沸点将原油分离为不同的馏分。烷烃是饱和烃，只含C–C单键。烯烃（CnH2n）是含有至少一个C=C双键的不饱和烃，可使溴水褪色。裂解是将长链烷烃分子断裂为较小的、更有用的烷烃和烯烃的过程。
Alcohols, such as ethanol (C₂H₅OH), contain the –OH functional group. Ethanol can be made by fermentation or from ethene. Alcohols react with carboxylic acids (which contain the –COOH group) to form esters in a reversible reaction, producing a sweet smell. Addition polymers are formed from alkenes when many small monomer units join together; condensation polymers form with the elimination of a small molecule such as water.
醇类，例如乙醇（C₂H₅OH），含有羟基（–OH）官能团。乙醇可通过发酵或由乙烯制得。醇与羧酸（含有–COOH官能团）发生可逆反应生成酯，产物具有芳香气味。加聚反应由烯烃单体聚合而成；缩聚反应则在生成聚合物的同时脱去水等小分子。
8. Chemical Analysis | 化学分析
A pure substance has a fixed melting and boiling point, while impurities lower the melting point and widen the melting range. Chromatography separates mixtures by their differing solubilities in a solvent, and Rf values can be used to identify substances.
纯物质具有固定的熔点和沸点，杂质会降低熔点并使熔程变宽。色谱法利用混合物中各组分在溶剂中溶解度的差异实现分离，Rf值可用于鉴定物质。
Rf = distance moved by substance / distance moved by solvent front
Rf = 物质移动距离 / 溶剂前沿移动距离
Common gas tests: oxygen relights a glowing splint; hydrogen produces a squeaky pop with a lighted splint; carbon dioxide turns limewater cloudy; chlorine bleaches damp litmus paper. Metal cations can be identified by flame tests (e.g. Na⁺ gives yellow, K⁺ gives lilac, Ca²⁺ gives orange-red) or by adding sodium hydroxide solution to form coloured precipitates. Anions: carbonates produce CO₂ with acid; halide ions give different coloured precipitates with silver nitrate; sulfate ions give a white precipitate with barium chloride.
常见的气体检验：氧气可使带火星的木条复燃；氢气遇点燃的木条发出爆鸣声；二氧化碳使石灰水变浑浊；氯气使湿润的石蕊试纸褪色。金属阳离子可通过焰色试验鉴定（如Na⁺呈黄色，K⁺呈淡紫色，Ca²⁺呈砖红色），或加入氢氧化钠溶液形成有色沉淀。阴离子：碳酸根加酸产生CO₂；卤素离子与硝酸银生成不同颜色的沉淀；硫酸根离子与氯化钡生成白色沉淀。
9. Chemistry of the Atmosphere | 大气化学
The Earth’s early atmosphere was mainly carbon dioxide with little oxygen, similar to present-day Mars and Venus. Over billions of years, photosynthesis by plants and algae reduced CO₂ levels and increased O₂ levels. Today, the atmosphere is approximately 78% nitrogen, 21% oxygen, and small amounts of other gases including CO₂ and water vapour.
地球早期大气主要是二氧化碳，氧气很少，与今天的火星和金星类似。数十亿年来，植物和藻类的光合作用降低了CO₂含量，增加了O₂含量。如今大气成分大约为78%的氮气，21%的氧气，以及少量其他气体，包括二氧化碳和水蒸气。
Greenhouse gases such as carbon dioxide, methane, and water vapour trap heat in the atmosphere, which keeps the planet warm. However, human activities like burning fossil fuels and farming have increased these gases, enhancing the greenhouse effect and causing global warming. Carbon footprints and mitigation strategies are part of environmental chemistry.
二氧化碳、甲烷和水蒸气等温室气体能够截留大气中的热量，使地球保持温暖。然而，燃烧化石燃料和农业活动等人类行为增加了这些气体的含量，加剧了温室效应，导致全球变暖。碳足迹和减排策略是环境化学的一部分。
10. Using Resources | 资源利用
Natural resources, such as minerals and fossil fuels, are finite. Sustainable development meets present needs without compromising those of future generations. Life cycle assessments (LCAs) evaluate the environmental impact of a product from raw material extraction to disposal. Recycling, reusing, and reducing materials all help conserve resources.
矿产和化石燃料等自然资源是有限的。可持续发展在满足当代需求的同时，不损害后代满足其需求的能力。生命周期评估（LCA）评价产品从原料提取到废弃整个过程的环境影响。回收、重复利用和减少材料使用都有助于节约资源。
Metals can be extracted from ores by reduction with carbon (for less reactive metals) or by electrolysis (for highly reactive metals such as aluminium). Alternative methods like bioleaching and phytomining use microorganisms or plants to extract metals from low-grade ores. Corrosion, especially the rusting of iron, can be prevented by barriers (paint, oil) or by sacrificial protection (e.g. galvanising with zinc). Alloys, ceramics, polymers, and composites are designed to have specific properties for various applications. The Haber process produces ammonia (NH₃) for fertilisers from nitrogen and hydrogen under high pressure and temperature with an iron catalyst.
金属可从矿石中提取：较不活泼的金属用碳还原，活泼金属（如铝）则用电解提取。生物浸出和植物修复等替代方法利用微生物或植物从低品位矿石中提取金属。腐蚀，特别是铁的生锈，可通过隔离层（油漆、油）或牺牲保护（如用锌镀锌）来防止。合金、陶瓷、聚合物和复合材料被设计为具有特定性能以满足不同应用。哈伯法在高温高压和铁催化剂作用下，用氮气和氢气生产化肥原料氨（NH₃）。
N₂ + 3H₂ ⇌ 2NH₃
氮气 + 氢气 ⇌ 氨气
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