📚 Covalent Bonding for IGCSE AQA Chemistry | IGCSE AQA 化学：共价键考点精讲
Covalent bonding is a core topic in IGCSE AQA Chemistry, explaining how non-metal atoms share electrons to achieve stable noble gas configurations. Mastering covalent bonding is essential for understanding the structures, properties, and real-world applications of countless substances, from water and carbon dioxide to diamond and graphite. This article provides a detailed, exam-focused breakdown of all key concepts you need to know.
共价键是 IGCSE AQA 化学的核心主题，它解释了非金属原子如何通过共享电子达到稳定的惰性气体电子构型。掌握共价键对于理解从水、二氧化碳到金刚石和石墨等无数物质的结构、性质及实际应用至关重要。本文将对所有需要掌握的关键概念进行详细的考点分解。
1. What is a Covalent Bond? | 什么是共价键？
A covalent bond is a strong chemical bond formed when two atoms share one or more pairs of electrons. This type of bonding typically occurs between non-metal atoms. By sharing electrons, each atom can achieve a full outer shell, attaining the stable electron configuration of a noble gas (the ‘octet rule’).
共价键是一种强化学键，当两个原子共享一对或多对电子时形成。这种键合通常发生在非金属原子之间。通过共享电子，每个原子都能获得完整的最外层，达到惰性气体的稳定电子构型（“八隅体规则”）。
2. Formation of Covalent Bonds | 共价键的形成
When non-metal atoms approach each other, their positively charged nuclei attract the shared pair(s) of negatively charged electrons. This electrostatic attraction between the nuclei and the shared electrons holds the atoms together, forming the covalent bond. Energy is released when a covalent bond is formed, making the bonded atoms more stable than separate atoms.
当非金属原子彼此靠近时，它们带正电的原子核吸引共享的带负电的电子对。原子核与共享电子之间的这种静电吸引力将原子结合在一起，形成共价键。形成共价键时会释放能量，使得成键原子比单独存在的原子更稳定。
3. Single, Double and Triple Bonds | 单键、双键和三键
Covalent bonds can be classified by the number of electron pairs shared. A single bond involves one shared pair of electrons (e.g., H – H, Cl – Cl). A double bond involves two shared pairs (e.g., O = O, in CO2). A triple bond involves three shared pairs (e.g., N ≡ N). Double and triple bonds are shorter and stronger than single bonds, which influences the reactivity and properties of molecules.
共价键可以根据共享电子对的数量分类。单键涉及一对共享电子（如 H – H，Cl – Cl）。双键涉及两对共享电子（如 O=O，CO2 中的键）。三键涉及三对共享电子（如 N≡N）。双键和三键比单键更短、更强，这会影响到分子的反应活性和性质。
4. Dot-and-Cross Diagrams | 点叉图
Dot-and-cross diagrams are used to represent covalent bonding. In these diagrams, only the outer shell electrons are shown. The electrons from one atom are drawn as dots and those from the other atom as crosses. This clearly shows which electrons are shared and which are lone pairs. For example, in methane (CH4), carbon shares four electron pairs with four hydrogen atoms; carbon’s outer electrons can be shown as dots and hydrogens’ as crosses. Always show all outer electrons, even those not involved in bonding.
点叉图用于表示共价键。在这些图中，只显示最外层电子。一个原子的电子用点表示，另一个原子的电子用叉表示。这样能清晰地显示哪些电子是共享的，哪些是孤对电子。例如，在甲烷（CH4）中，碳与四个氢原子共享四对电子；碳的最外层电子可以用点表示，氢的电子用叉表示。务必画出所有外层电子，即使是那些未参与成键的电子。
5. Simple Molecular Substances | 简单分子物质
Simple molecules include H2, Cl2, O2, N2, H2O, CH4, NH3, HCl, and CO2. These molecules contain a small number of atoms held together by strong covalent bonds within the molecule. However, between molecules, there are only weak intermolecular forces (van der Waals forces). It is vital to distinguish between the strong covalent bonds inside a molecule and the weak forces between molecules – a common exam pitfall.
简单分子包括 H2、Cl2、O2、N2、H2O、CH4、NH3、HCl 和 CO2。这些分子内含有少量原子，原子间通过强共价键结合在一起。然而，分子之间仅存在微弱的分子间作用力（范德华力）。区分分子内部的强共价键和分子间的微弱作用力至关重要——这是常见的考试陷阱。
6. Properties of Simple Molecular Compounds | 简单分子化合物的性质
Simple molecular substances have low melting and boiling points because only the weak intermolecular forces need to be overcome for melting or boiling. They are usually gases or liquids at room temperature but can be solids (e.g., iodine, I2, which has enough intermolecular forces to be solid). They do not conduct electricity in any state because they have no free-moving ions or electrons; the molecules are neutral. Many are insoluble in water but soluble in organic solvents.
简单分子物质具有较低的熔点和沸点，因为熔化或沸腾时只需克服微弱的分子间作用力。它们在室温下通常为气体或液体，但也可能是固体（如碘 I2，其分子间作用力足够大而呈固态）。它们在任何状态下都不导电，因为没有自由移动的离子或电子；分子是电中性的。许多简单分子不溶于水，但可溶于有机溶剂。
7. Giant Covalent Structures: Diamond | 巨型共价结构：金刚石
Diamond is a giant covalent structure. Each carbon atom forms four strong covalent bonds with four other carbon atoms, creating a rigid, three-dimensional tetrahedral network. This structure makes diamond the hardest natural substance, with a very high melting point (over 3500 °C). Diamond does not conduct electricity because all electrons are fixed in bonds; there are no delocalised electrons or free ions.
金刚石是一种巨型共价结构。每个碳原子与其他四个碳原子形成四个强共价键，形成刚性的三维四面体网络。这种结构使金刚石成为最硬的天然物质，熔点极高（超过 3500 °C）。金刚石不导电，因为所有电子都被固定在化学键中，没有离域电子或自由离子。
8. Giant Covalent Structures: Graphite | 巨型共价结构：石墨
Graphite is also a giant covalent structure but with a different arrangement. Each carbon atom bonds to three others, forming flat hexagonal layers. The layers are held together by weak intermolecular forces, allowing them to slide over each other – this makes graphite soft and slippery, useful as a lubricant and in pencils. Graphite conducts electricity because each carbon atom has one delocalised electron that can move freely between the layers, carrying charge.
石墨也是一种巨型共价结构，但排列不同。每个碳原子与另外三个碳原子成键，形成扁平的六边形层。层与层之间通过微弱的分子间作用力结合，这使得它们可以相互滑动——因此石墨柔软且具有润滑性，可用作润滑剂和铅笔芯。石墨能导电，因为每个碳原子有一个离域电子，可在层间自由移动，携带电荷。
9. Silicon Dioxide (Silica) | 二氧化硅（硅石）
Silicon dioxide (SiO2) has a giant covalent structure similar to diamond. Each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a continuous tetrahedral network. It has very high melting and boiling points (over 1600 °C), is hard, and does not conduct electricity. It is the main component of sand and quartz. Exam boards often ask you to compare its structure with diamond or explain its high melting point.
二氧化硅（SiO2）具有类似金刚石的巨型共价结构。每个硅原子与四个氧原子结合，每个氧原子与两个硅原子结合，形成连续的四体网络。它具有极高的熔点和沸点（超过 1600 °C），质地坚硬，不导电。它是沙子和石英的主要成分。考试时常要求你将其结构与金刚石进行比较，或解释其高熔点的原因。
10. Comparing Diamond and Graphite | 金刚石与石墨的比较
A common exam question asks to compare diamond and graphite. Both are allotropes of carbon, have giant covalent structures, and very high melting points. However, they differ in bonding, hardness, and electrical conductivity. The following table summarises the key differences.
常见的考试题目要求比较金刚石和石墨。二者都是碳的同素异形体，具有巨型共价结构及极高的熔点。但是，它们在成键、硬度和导电性上存在差异。下表总结了关键的区别。
| Property | Diamond | Graphite |
|---|---|---|
| Bonding per C | 4 covalent bonds | 3 covalent bonds + 1 delocalised electron |
| Structure | 3D tetrahedral network | Hexagonal layers |
| Hardness | Very hard | Soft and slippery |
| Electrical conductivity | No (no free electrons) | Yes (delocalised electrons between layers) |
| Melting point | Very high (~3550 °C) | Very high (sublimes ~3650 °C) |
下表用中文表述相同差异：
| 特性 | 金刚石 | 石墨 |
|---|---|---|
| 每个碳原子成键 | 4 个共价键 | 3 个共价键 + 1 个离域电子 |
| 结构 | 三维四面体网络 | 六边形层状结构 |
| 硬度 | 非常硬 | 软而滑 |
| 导电性 | 不导电（无自由电子） | 导电（层间有离域电子） |
| 熔点 | 极高（约 3550 °C） | 极高（升华约 3650 °C） |
11. Intermolecular Forces | 分子间作用力
In simple molecular substances, the forces of attraction between molecules are known as intermolecular forces (van der Waals forces). These are much weaker than covalent bonds. The strength of these forces increases with the size of the molecule (larger molecules have more electrons and thus stronger intermolecular forces), leading to higher melting and boiling points among similar substances. For example, iodine (I2) is a solid while chlorine (Cl2) is a gas, because I2 molecules have many more electrons and therefore stronger intermolecular forces.
在简单分子物质中，分子之间的吸引力被称为分子间作用力（范德华力）。这些力比共价键弱得多。这些力的强度随分子大小的增加而增加（较大的分子具有更多的电子，因此分子间作用力更强），在相似物质中导致熔点和沸点更高。例如，碘（I2）是固体，而氯（Cl2）是气体，因为 I2 分子具有多得多的电子，因此分子间作用力更强。
12. Common Exam Mistakes & Tips | 常见考试错误与提示
Students often confuse intermolecular forces with covalent bonds. Remember: covalent bonds are strong and within molecules; intermolecular forces are weak and between molecules. When asked to explain the properties of diamond or graphite, always refer to their giant covalent structure and the strong covalent bonds throughout (or delocalised electrons in graphite). Avoid saying that simple molecular substances conduct electricity when melted – they do not, because there are no ions. When drawing dot-and-cross diagrams, show only outer shell electrons, use different symbols for different atoms, and show bonding pairs as well as lone pairs. Finally, be precise with terminology: ‘intermolecular forces’ not ‘weak bonds’.
学生经常混淆分子间作用力与共价键。记住：共价键很强，存在于分子内部；分子间作用力很弱，存在于分子之间。当要求解释金刚石或石墨的性质时，一定要提到其巨型共价结构及贯穿整个结构的强共价键（或石墨中的离域电子）。不要错误地说简单分子物质在熔化时会导电——它们不导电，因为没有离子。在绘制点叉图时，只显示最外层电子，对不同原子使用不同的符号，并画出成键电子对和孤对电子。最后，术语要准确：‘分子间作用力’，而不是‘弱键’。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导Cancel reply