📚 Organic Chemistry Basics | 有机化学基础
Organic chemistry is the branch of chemistry that studies the structure, properties, and reactions of carbon-containing compounds. Almost all organic compounds contain carbon and hydrogen, and many also include oxygen, nitrogen, or halogens. On the GCSE CCEA Chemistry specification, you need to understand the basic families of organic molecules – particularly alkanes and alkenes – their patterns of reactivity, and how they can be used to make useful materials like plastics.
有机化学是研究含碳化合物的结构、性质与反应的分支学科。绝大多数有机化合物都含有碳和氢，许多还含有氧、氮或卤素。在 GCSE CCEA 化学考纲中，你需要掌握基本的有机分子家族——特别是烷烃和烯烃——它们的反应规律，以及如何利用它们制造塑料等有用材料。
1. What Makes Carbon Special | 碳为何特别
Carbon atoms have four electrons in their outer shell, so they can form four strong covalent bonds with other atoms. This allows carbon to build up long chains, branched structures, and rings – forming the backbone of millions of different compounds. The ability of carbon to bond with itself (catenation) is the foundation of organic chemistry.
碳原子最外层有四个电子，因此可以与其他原子形成四个牢固的共价键。这使得碳能够构建长链、支链和环状结构，构成数百万种不同化合物的骨架。碳原子自相结合（链接）的能力是有机化学的基础。
A single covalent bond between two carbon atoms is represented by a single line ( C– double bond by two lines ( C=C ). You will see these in displayed and structural formulas.
两个碳原子之间的单共价键用一条线表示 (C–C)，双键用两条线表示 (C=C)。在完整显示式和结构式中你会看到这些表示。
2. Hydrocarbons: Alkanes and Alkenes | 烃：烷烃与烯烃
A hydrocarbon is a compound made only of carbon and hydrogen atoms. The two main families you need to know are alkanes and alkenes. Alkanes contain only single bonds between carbon atoms – they are saturated hydrocarbons. Alkenes contain at least one carbon-carbon double bond – they are unsaturated.
烃是仅由碳和氢原子组成的化合物。你需要了解两个主要家族：烷烃和烯烃。烷烃的碳原子之间只含单键——它们是饱和烃。烯烃至少含有一个碳碳双键——它们是不饱和烃。
Saturated compounds cannot undergo addition reactions because all carbon bonds are already fully used. Unsaturated compounds, however, have the double bond that can open up to let other atoms join on.
饱和化合物不能发生加成反应，因为所有的碳键都已完全使用。但不饱和化合物的双键可以打开，让其他原子加上去。
3. The Alkane Homologous Series | 烷烃同系物
A homologous series is a family of compounds with the same general formula, similar chemical properties, and a gradual change in physical properties. Alkanes form such a series with the general formula CₙH₂ₙ₊₂. The first four straight-chain alkanes are:
同系物是指具有相同通式、相似的化学性质以及物理性质逐渐变化的一系列化合物。烷烃就形成这样一个同系物系列，通式为 CₙH₂ₙ₊₂。前四个直链烷烃为：
- Methane (CH₄) – 甲烷
- Ethane (C₂H₆) – 乙烷
- Propane (C₃H₈) – 丙烷
- Butane (C₄H₁₀) – 丁烷
As the carbon chain length increases, the boiling point, viscosity, and melting point increase. This is because larger molecules have stronger intermolecular forces (London dispersion forces) that require more energy to overcome.
随着碳链长度增加，沸点、粘度和熔点都升高。这是因为较大的分子具有更强的分子间作用力（伦敦色散力），需要更多能量来克服。
4. Naming Alkanes | 烷烃的命名
The names of organic compounds follow the IUPAC system. For the first four straight-chain alkanes, the prefixes are meth- (1 carbon), eth- (2), prop- (3), but- (4), followed by the suffix -ane. This tells you the compound is an alkane. When naming alkanes, always count the longest continuous carbon chain, and if there are side chains, they are named as alkyl groups like methyl (CH₃–) or ethyl (C₂H₅–).
有机化合物的命名遵循 IUPAC 系统。对于前四个直链烷烃，前缀是 meth-（1个碳）、eth-（2个）、prop-（3个）、but-（4个），后加后缀 -ane，表示该化合物是烷烃。命名烷烃时，始终数最长连续碳链；如果有支链，它们被命名为烷基，如甲基 (CH₃–) 或乙基 (C₂H₅–)。
For example, a four-carbon chain with a methyl group on the second carbon is called 2-methylpropane. The number tells you which carbon the group is attached to. CCEA GCSE expects you to name and draw the first four alkanes and simple branched isomers up to four carbons.
例如，一个四碳链在第二个碳上连有一个甲基，称为 2-甲基丙烷。数字告诉你基团连接在哪个碳上。CCEA 的 GCSE 考试要求能命名并画出前四个烷烃以及最多四个碳的简单支链异构体。
5. Drawing Formulas and Isomers | 画结构式与异构体
You need to be able to represent alkanes using molecular formulas (e.g. C₄H₁₀), displayed formulas (showing all bonds and atoms), and structural formulas (showing groups like CH₃–CH₂–CH₂–CH₃). Butane (C₄H₁₀) has a straight-chain isomer and a branched isomer: 2-methylpropane. Compounds with the same molecular formula but different structural arrangements are called isomers.
你需要能够用分子式（如 C₄H₁₀）、完整显示式（显示所有键和原子）和结构式（如 CH₃–CH₂–CH₂–CH₃）来表示烷烃。丁烷 (C₄H₁₀) 有一个直链异构体和一个支链异构体：2-甲基丙烷。分子式相同但结构排列不同的化合物称为异构体。
Isomers have different physical properties, such as boiling points, because the shape of the molecule affects how closely they can pack together and the strength of intermolecular forces.
异构体具有不同的物理性质，例如沸点，因为分子的形状影响它们堆积的紧密程度以及分子间作用力的强度。
6. Reactions of Alkanes: Combustion | 烷烃的反应：燃烧
Alkanes are relatively unreactive because of the strong C–C and C–H bonds. Their most important reaction is combustion. In a plentiful supply of oxygen (complete combustion), alkanes burn to form carbon dioxide and water, releasing a lot of heat energy. For example, the complete combustion of methane is:
烷烃由于 C–C 和 C–H 强键而相对不活泼。它们最重要的反应是燃烧。在氧气充足的情况下（完全燃烧），烷烃燃烧生成二氧化碳和水，并放出大量热能。例如，甲烷的完全燃烧方程式为：
CH₄ + 2O₂ → CO₂ + 2H₂O
If the oxygen supply is limited (incomplete combustion), poisonous carbon monoxide (CO) and/or soot (carbon particles, C) are formed instead of, or alongside, CO₂. Incomplete combustion is dangerous because CO binds to haemoglobin in blood, reducing oxygen transport.
如果氧气供应有限（不完全燃烧），则生成有毒的一氧化碳 (CO) 和/或碳粒（烟炱，C），代替或伴随 CO₂ 产生。不完全燃烧是危险的，因为 CO 与血液中的血红蛋白结合，降低输氧能力。
Alkanes are useful fuels: methane is the main component of natural gas, while propane and butane are used in camping gas canisters (LPG). Their combustion provides energy for heating and cooking.
烷烃是很有用的燃料：甲烷是天然气的主要成分，丙烷和丁烷用于野营燃气罐（液化石油气）。它们的燃烧为取暖和烹饪提供能量。
7. The Alkene Homologous Series | 烯烃同系物
bond. The general formula for alkenes with one double bond is CₙH₂ₙ. The first two alkenes are ethene (C₂H₄) and propene (C₃H₆). Unlike alkanes, alkenes cannot have a one‑carbon molecule because a double bond requires at least two carbon atoms.
烯烃是含至少一个 C=C 双键的不饱和烃。含一个双键的烯烃通式为 CₙH₂ₙ。前两个烯烃是乙烯 (C₂H₄) 和丙烯 (C₃H₆)。与烷烃不同，烯烃不能有一个碳的分子，因为双键至少需要两个碳原子。
When naming alkenes, the suffix is -ene. The position of the double bond is indicated by a number. For butene (C₄H₈), there are two positional isomers: but-1-ene and but-2-ene, where the numbers show the first carbon of the double bond. You must number the chain from the end nearest the double bond.
命名烯烃时，后缀为 -ene。双键的位置用数字标明。对于丁烯 (C₄H₈)，有两个位置异构体：丁-1-烯和丁-2-烯，数字表示双键的第一个碳。你必须从距离双键最近的一端开始给碳链编号。
8. Addition Reactions of Alkenes | 烯烃的加成反应
lectron density, making alkenes much more reactive than alkanes. Alkenes undergo addition reactions, where the double bond opens up and two new atoms attach across the carbons. The main addition reactions you must know for GCSE are:
C=C 双键是一个电子密度较高的区域，这使得烯烃比烷烃活泼得多。烯烃发生加成反应，双键打开，两个新原子加到这两个碳上。GCSE 必须了解的主要加成反应有：
- Addition of hydrogen (hydrogenation): alkane. This requires a nickel catalyst and heat. Ethene becomes ethane: C₂H₄ + H₂ → C₂H₆.
- 加成氢气（氢化）： 烯烃 + H₂ → 烷烃。需要镍催化剂并加热。乙烯变为乙烷：C₂H₄ + H₂ → C₂H₆。
- Addition of halogens (halogenation): m temperature. Ethene reacts with bromine to form 1,2-dibromoethane: C₂H₄ + Br₂ → C₂H₄Br₂.
- 加成卤素（卤化）： 烯烃 + Br₂ → 二溴代烷。室温即可发生。乙烯与溴反应生成 1,2-二溴乙烷：C₂H₄ + Br₂ → C₂H₄Br₂。
- Addition of steam (hydration): acid catalyst, high temperature and pressure. Ethene becomes ethanol: C₂H₄ + H₂O → C₂H₅OH.
- 加成水蒸气（水化）： 烯烃 + H₂O → 醇。需要磷酸催化剂，高温高压。乙烯变为乙醇：C₂H₄ + H₂O → C₂H₅OH。
These reactions turn an unsaturated compound into a saturated one, which makes addition reactions a useful way to distinguish alkenes from alkanes.
这些反应将不饱和化合物转变为饱和化合物，使得加成反应成为区分烯烃与烷烃的有效方法。
9. Testing for Unsaturation with Bromine Water | 用溴水检验不饱和性
Bromine water is an orange-brown solution. When it is shaken with an alkane, nothing happens – the colour stays. But when shaken with an alkene, the orange-brown colour quickly disappears (decolourises) because the bromine adds across the double bond. This is the standard test for unsaturation.
溴水是一种橙棕色溶液。当它与烷烃一起摇动时，没有变化——颜色保持。但当它与烯烃摇动时，橙棕色迅速消失（褪色），因为溴加成到双键上。这是检验不饱和性的标准方法。
uires UV light. So immediate decolourisation of bromine water indicates a C=C double bond.
对于烯烃，该反应不需要紫外光或加热，而烷烃与卤素的取代反应则需紫外光。所以溴水立即褪色表明存在 C=C 双键。
10. Addition Polymerisation | 加成聚合
Alkenes can join together to form very long chains called polymers. This process is addition polymerisation. Under high pressure and with a catalyst, many small alkene molecules (monomers) open their double bonds and link up to form a saturated polymer chain. No other products are made.
烯烃可以连接在一起形成很长的链，称为聚合物。这一过程是加成聚合。在高压和催化剂作用下，许多小的烯烃分子（单体）打开它们的双键并连接起来，形成饱和的聚合物链。没有其他产物生成。
For example, ethene monomers form poly(ethene) – commonly known as polythene. The reaction can be represented as:
例如，乙烯单体形成聚（乙烯）——俗称聚乙烯。反应可表示为：
n C₂H₄ → –(CH₂–CH₂)–ₙ
Poly(propene) is formed from propene monomers. The repeating unit is the part of the polymer that repeats along the chain, and its formula lacks the double bond. You should be able to draw the repeating unit for a given monomer and vice versa.
聚（丙烯）由丙烯单体形成。重复单元是聚合物链上不断重复的部分，其结构中不含双键。你应该能从给定单体的结构画出重复单元，反之亦然。
11. Plastics and Their Properties | 塑料及其性质
Addition polymers make up a large class of materials called plastics. Their properties depend on the monomer used and the reaction conditions. Poly(ethene) can be made as low-density (LDPE) or high-density (HDPE) by altering pressure and catalyst. LDPE is flexible and used for plastic bags, while HDPE is stiffer and used for bottles and pipes.
加成聚合物构成了一大类称为塑料的材料。它们的性质取决于所用的单体和反应条件。通过改变压力和催化剂，聚（乙烯）可制成低密度 (LDPE) 或高密度 (HDPE) 两种。LDPE 柔韧，用于塑料袋；HDPE 较硬，用于瓶子和管道。
Most addition polymers are non-biodegradable because the strong C–C backbone is resistant to microbial breakdown. This causes disposal problems. Recycling, reusing, and developing biodegradable polymers are ways to reduce plastic waste. CCEA GCSE Chemistry links this to environmental chemistry and sustainability.
大多数加成聚合物不可生物降解，因为强韧的 C–C 主链能抵抗微生物的分解。这导致了处理问题。回收、重复使用和开发可生物降解的聚合物是减少塑料废弃物的途径。CCEA GCSE 化学将此与环境化学和可持续发展联系起来。
12. Summary of Key Comparisons | 关键对比小结
| Property / 性质 | Alkanes / 烷烃 | Alkenes / 烯烃 |
|---|---|---|
| General formula / 通式 | CₙH₂ₙ₊₂ | CₙH₂ₙ |
| Saturation / 饱和度 | Saturated (only C–C) / 饱和 | Unsaturated (C=C) / 不饱和 |
| Reaction with Br₂ water / 与溴水反应 | No immediate change (requires UV) / 无即时变化 | Decolourises quickly / 迅速褪色 |
| Typical reaction / 典型反应 | Combustion / 燃烧 | Addition polymerisation / 加成聚合 |
Understanding these fundamentals will help you tackle the GCSE CCEA Chemistry questions on organic chemistry, including naming compounds, drawing structures, writing equations, and explaining reactions. Remember that organic families obey clear patterns, and once you master the first few members, the rest follow logically.
掌握这些基础知识后，你将能够应对 GCSE CCEA 化学中有机化学的题目，包括命名化合物、画结构式、书写方程式和解释反应。请记住，有机家族遵循清晰的规律，一旦你掌握了前几个成员，其余的也会顺理成章。
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