📚 Mastering Covalent Bonding for GCSE CCEA Chemistry | GCSE CCEA 化学：共价键考点精讲
Covalent bonding is a fundamental concept in GCSE CCEA Chemistry. It explains how non-metal atoms join together by sharing electrons to form molecules or giant structures. This revision guide covers everything you need to know about covalent bonding, from simple dot-and-cross diagrams to the properties of diamond and graphite, helping you to master the key points confidently.
共价键是 GCSE CCEA 化学中的核心概念。它解释了非金属原子如何通过共享电子结合在一起，形成分子或巨型结构。本复习指南涵盖共价键的方方面面，从简单的点叉图到金刚石与石墨的性质，助你全面掌握考点，自信应试。
1. What is a Covalent Bond? | 什么是共价键？
A covalent bond forms when two non-metal atoms share one or more pairs of electrons. The shared electrons are attracted to the positively charged nuclei of both atoms, creating a strong electrostatic attraction that holds the atoms together.
共价键形成于两个非金属原子之间，它们共享一对或多对电子。共享电子同时被两个原子的带正电原子核吸引，产生强大的静电引力，将原子牢牢结合在一起。
Atoms form covalent bonds to achieve a stable electron configuration similar to that of a noble gas. For most atoms, this means completing an outer shell of eight electrons (the octet rule). Hydrogen is an exception; it only needs two electrons to become stable like helium.
原子形成共价键是为了达到与惰性气体类似的稳定电子构型。对大多数原子而言，这意味着最外层填满八个电子（八隅体规则）。氢是例外，它只需要两个电子即可像氦一样稳定。
2. Formation of Covalent Bonds: Sharing Electrons | 共价键的形成：共享电子
In a covalent bond, each atom contributes at least one electron to a shared pair. This shared pair is often represented as a line between atoms in structural formulas. Before bonding, atoms may have unpaired electrons that pair up when orbitals overlap.
在共价键中，每个原子至少提供一个电子形成共享电子对。这一对电子在结构式中常被表示为原子之间的一条短线。成键前，原子可能有未成对电子，在轨道重叠时这些电子配对形成共价键。
For example, a hydrogen molecule (H₂) forms when two hydrogen atoms each provide one electron. The shared pair gives both atoms a helium-like configuration (1s²). The bond can be written as H–H or H:H.
例如，氢分子 (H₂) 形成时，两个氢原子各提供一个电子。共享电子对使两个原子都达到了类似氦的构型 (1s²)。该键可写作 H–H 或 H:H。
A chlorine molecule (Cl₂) is another classic example. Each chlorine atom has seven valence electrons. By sharing one electron each, both atoms complete their octet. The covalent bond is shown as Cl–Cl, with the remaining electrons represented as lone pairs in a dot-and-cross diagram: each chlorine atom ends up with three lone pairs and one bonding pair.
氯分子 (Cl₂) 是另一个典型例子。每个氯原子有七个价电子。通过各提供一个电子共享，两个原子都完成了八隅体。共价键表示为 Cl–Cl，在点叉图中，其余的电子表示为孤对电子：每个氯原子最终有三对孤对电子和一对成键电子。
3. Single, Double and Triple Bonds | 单键、双键与三键
When atoms share one pair of electrons, a single covalent bond forms. If they share two pairs, a double bond results (often shown with =). Sharing three pairs gives a triple bond (≡). The bond strength increases from single to triple, while the bond length decreases.
当原子共享一对电子时，形成单键。共享两对电子形成双键（常用 = 表示）。共享三对电子形成三键（≡）。从单键到三键，键能增大，键长缩短。
Oxygen gas (O₂) contains a double bond: O=O. Each oxygen atom shares two electrons, so both atoms complete their octets. Nitrogen gas (N₂) features a very strong triple bond: N≡N. Carbon dioxide (CO₂) exhibits two double bonds: O=C=O, making the molecule linear.
氧气 (O₂) 含有一个双键：O=O。每个氧原子共享两个电子，使两者都完成八隅体。氮气 (N₂) 含有一个非常强的三键：N≡N。二氧化碳 (CO₂) 有两个双键：O=C=O，这使分子呈直线形。
Carbon can form multiple bonds in organic compounds and in allotropes. Ethene (C₂H₄) has a carbon-carbon double bond, while ethyne (C₂H₂) has a carbon-carbon triple bond. Knowing how to count shared pairs is essential for drawing correct Lewis structures.
碳在有机化合物和同素异形体中可形成多重键。乙烯 (C₂H₄) 有一个碳碳双键，乙炔 (C₂H₂) 有一个碳碳三键。能够正确计算共享电子对的数量，对于画出正确的路易斯结构至关重要。
4. Drawing Dot-and-Cross Diagrams | 绘制点叉图
Dot-and-cross diagrams are used to show the outer-shell electrons of atoms in a molecule. Electrons from different atoms are shown using different symbols (dots for one, crosses for another) so that the origin of each electron can be identified.
点叉图用来表示分子中原子的最外层电子。不同原子的电子用不同符号表示（一个用点，另一个用叉），以便区分每个电子的来源。
Steps to draw a diagram: (1) Count the total valence electrons. (2) Arrange the atoms – usually the atom with the most unpaired electrons or the least electronegative goes in the centre. (3) Place bonding pairs between atoms. (4) Distribute remaining electrons as lone pairs to satisfy the octet rule (or duet for H).
绘制步骤：(1) 计算总的价电子数。(2) 排列原子——通常未成对电子最多或电负性最小的原子放在中心。(3) 在原子之间放置成键电子对。(4) 将余下的电子作为孤对电子分配，以满足八隅体规则（氢满足二电子规则）。
Example: water (H₂O). Oxygen is central. Oxygen has six valence electrons; each hydrogen has one. Two bonding pairs are formed between O and each H, giving four shared electrons. The remaining four electrons on oxygen form two lone pairs. The shape is bent due to lone pair repulsion.
例子：水 (H₂O)。氧为中心原子。氧有六个价电子，每个氢有一个。氧与每个氢之间形成两个成键电子对，共用四个电子。氧上剩余的四个电子形成两对孤对电子。由于孤对电子地排斥，分子形状为弯曲形。
5. Simple Molecular Substances: Structure and Properties | 简单分子物质：结构与性质
Substances made of small molecules, such as H₂O, CO₂, CH₄ and I₂, are called simple molecular substances. Their atoms are held together by strong covalent bonds inside the molecules, but between the molecules there are only weak intermolecular forces (van der Waals’ forces or hydrogen bonds).
由小分子组成的物质，如 H₂O、CO₂、CH₄ 和 I₂，称为简单分子物质。分子内部原子通过强共价键结合，但分子之间仅存在微弱的分子间作用力（范德华力或氢键）。
Because little energy is needed to overcome these weak intermolecular forces, simple molecular substances have low melting and boiling points. They are often gases or liquids at room temperature. Their volatility increases with lower molecular mass and simpler shapes.
由于克服这些微弱分子间作用力所需能量很少，简单分子物质具有较低的熔点和沸点。它们在室温下常为气体或液体。分子质量越小、形状越简单，越易挥发。
Simple molecular substances do not conduct electricity in any state because they have no mobile charged particles – molecules are neutral and electrons are locked in covalent bonds or lone pairs. Even when dissolved in water, most simple molecules (except those that react with water) remain as neutral entities and do not carry current.
简单分子物质在任何状态下都不导电，因为它们没有可移动的带电粒子——分子是中性的，电子被锁定在共价键或孤对电子中。即使溶于水，大多数简单分子（与水反应的除外）仍保持中性，不传导电流。
6. Giant Covalent Structures (Macromolecules) | 巨型共价结构（高分子）
Some non-metal elements and compounds form giant covalent structures, also known as covalent networks or macromolecules. In these structures, billions of atoms are joined by strong covalent bonds in a continuous three-dimensional (or two-dimensional) lattice. There are no separate molecules; the whole crystal is essentially one gigantic molecule.
某些非金属元素和化合物形成巨型共价结构，也称共价网络或高分子。在这些结构中，数十亿个原子通过强共价键连接成一个连续的三维（或二维）晶格。不存在单独的分子；整个晶体基本上就是一个巨大的分子。
Common examples include diamond, graphite, silicon dioxide (silica) and silicon carbide. The bonding in these substances gives them very different properties from simple molecular substances. They usually have very high melting and boiling points because strong covalent bonds must be broken throughout the lattice for the substance to melt or boil.
常见例子包括金刚石、石墨、二氧化硅（石英）和碳化硅。这些物质中的键合使得它们的性质与简单分子物质截然不同。它们通常具有极高的熔点和沸点，因为要熔化或沸腾必须破坏整个晶格中的强共价键。
Giant covalent structures are generally insoluble in water and most solvents. Some, like graphite, can conduct electricity, while others are insulators. Their hardness varies widely depending on the bonding arrangement.
巨型共价结构通常不溶于水和大多数溶剂。有些（如石墨）可以导电，而另一些则是绝缘体。它们的硬度因键合排列方式而有很大差异。
7. Diamond: Structure and Properties | 金刚石：结构与性质
Diamond is a form of pure carbon where each carbon atom forms four strong single covalent bonds with four neighbouring carbon atoms in a tetrahedral arrangement. This three-dimensional network extends throughout the crystal.
金刚石是纯碳的一种形式，其中每个碳原子与四个相邻碳原子形成四个强共价单键，呈四面体排列。这个三维网络贯穿整个晶体。
Because all valence electrons are used in bonding, diamond does not have free electrons or mobile ions. Consequently, diamond does not conduct electricity – it is an excellent electrical insulator.
由于所有价电子都用于成键，金刚石没有自由电子或可移动离子。因此，金刚石不导电——它是一种优良的电绝缘体。
Diamond is the hardest known natural substance. Its rigid, strongly bonded framework makes it extremely resistant to scratching and deformation. It has a very high melting point (above 3500°C) and is an excellent thermal conductor because lattice vibrations transmit heat efficiently.
金刚石是迄今已知最坚硬的天然物质。其刚性、强键合的框架使其极耐刮擦和形变。它具有极高的熔点（超过 3500°C），并且由于晶格振动能高效传热，它还是优良的热导体。
8. Graphite: Structure and Properties | 石墨：结构与性质
Graphite is another allotrope of carbon. In graphite, each carbon atom forms three covalent bonds with three other carbon atoms within a flat two-dimensional layer. This leaves one delocalised electron per carbon atom, which can move freely between the layers.
石墨是碳的另一种同素异形体。在石墨中，每个碳原子与同一平面内的三个其他碳原子形成三个共价键，剩下一个离域电子可在层间自由移动。
The layers are held together by weak van der Waals’ forces, allowing them to slide over each other easily. This explains why graphite feels slippery and is used as a lubricant and in pencil “lead”. Graphite can conduct electricity along its layers because of the mobile delocalised electrons, making it useful for electrodes and batteries.
层与层之间通过微弱的范德华力结合，使它们能够轻易滑动。这解释了为什么石墨手感滑腻，可用作润滑剂和铅笔“芯”。由于存在可移动的离域电子，石墨可沿层面导电，因此常用于电极和电池。
Like diamond, graphite has a very high melting point because the covalent bonds within each layer are strong. However, its anisotropy means that its properties differ sharply in directions parallel to and perpendicular to the layers.
与金刚石相似，石墨具有极高的熔点，因为每层内的共价键很强。然而，其各向异性意味着平行于层面和垂直于层面方向上的性质截然不同。
9. Silicon Dioxide (Silica) and Its Properties | 二氧化硅（硅石）及其性质
Silicon dioxide (SiO₂), commonly found as quartz or sand, has a giant covalent structure similar to diamond, but with silicon and oxygen atoms. Each silicon atom is bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a continuous network with the overall formula SiO₂.
二氧化硅 (SiO₂)，常见于石英或沙子中，具有与金刚石类似的巨型共价结构，但包含硅原子和氧原子。每个硅原子与四个氧原子键合，每个氧原子与两个硅原子键合，形成一个连续网络，整体化学式为 SiO₂。
Silicon dioxide is very hard, has a very high melting point (about 1710°C) and does not conduct electricity under normal conditions. Like diamond, all electrons are localised in covalent bonds, so there are no free charged particles.
二氧化硅非常坚硬，熔点极高（约 1710°C），在正常条件下不导电。与金刚石一样，所有电子都定域在共价键中，因此没有自由带电粒子。
It is insoluble in water but can react with alkalis and hydrofluoric acid. Its hardness and thermal stability make it useful in glassmaking, ceramics and as a semiconductor when processed (but pure silica is an insulator in the GCSE context).
它不溶于水，但能与碱和氢氟酸反应。其硬度和热稳定性使其在玻璃制造、陶瓷及加工后用作半导体方面有重要用途（但在 GCSE 范畴内，纯二氧化硅是绝缘体）。
10. Comparing Bonding and Structure | 比较化学键与结构
Understanding the differences between covalent, ionic and metallic bonding is vital for explaining trends in properties. Covalent substances can be simple molecular (low mp, non-conducting) or giant covalent (high mp, variable conductivity).
理解共价键、离子键和金属键之间的差异，对于解释性质变化趋势至关重要。共价物质可以是简单分子（低熔点，不导电）或巨型共价结构（高熔点，导电性各异）。
Below is a summary table of common substances and their bond types:
| Substance | Bonding | Structure type | Melting point | Electrical conductivity |
|---|---|---|---|---|
| Oxygen (O₂) | Covalent (double bond) | Simple molecular | Very low | None |
| Water (H₂O) | Covalent (single bonds) | Simple molecular | Low (0°C) | None (pure) |
| Diamond (C) | Covalent (single bonds) | Giant covalent | Very high (>3500°C) | None |
| Graphite (C) | Covalent (single bonds) + delocalised electrons | Giant covalent layered | Very high | Yes (along layers) |
| Silicon dioxide (SiO₂) | Covalent (single bonds) | Giant covalent | Very high (1710°C) | None |
When answering exam questions, always link the observed property to the type of structure and bonding. For example: “Diamond has a high melting point because it is a giant covalent lattice and disruptive melting requires breaking many strong covalent bonds.”
回答考题时，务必将观察到的性质与结构和键合类型联系起来。例如：“金刚石具有高熔点，因为它是一个巨型共价晶格，要破坏其结构熔化需要断裂大量强共价键。”
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