📚 Covalent Bonding: GCSE OCR Chemistry Key Points | GCSE OCR 化学：共价键 考点精讲
Covalent bonding is a fundamental type of chemical bond that holds together many of the substances we encounter daily, from the water we drink to the gases in the air. This revision guide covers all the essential knowledge you need for the GCSE OCR Chemistry exam, including how covalent bonds form, how to represent them, the contrasting properties of simple molecules and giant covalent structures, and key examples like diamond, graphite, and silicon dioxide.
共价键是一种基础化学键，将我们日常接触的许多物质结合在一起——从饮用水到空气中的气体。这篇复习指南涵盖 GCSE OCR 化学考试所需的所有核心知识，包括共价键的形成方式、如何表示共价键、简单分子与巨型共价结构的性质对比，以及金刚石、石墨和二氧化硅等重要实例。
1. What Is Covalent Bonding? | 什么是共价键？
A covalent bond is a strong electrostatic attraction between the nuclei of two non-metal atoms and the shared pair of electrons between them. Unlike ionic bonding, where electrons are transferred, covalent bonding involves the sharing of electrons so that each atom can achieve a stable full outer shell (or a noble gas configuration).
共价键是两个非金属原子核与它们之间共享电子对之间强烈的静电吸引力。与电子发生转移的离子键不同，共价键通过共享电子使每个原子都能达到稳定的满外层（即惰性气体构型）。
This sharing usually occurs because both atoms have high electronegativity – a strong desire to gain electrons. By pooling their electrons into a shared pair, both nuclei are attracted to the same electrons, effectively satisfying the octet rule (or duet rule for hydrogen).
这种共享通常是因为两个原子都有很高的电负性——非常渴望获得电子。通过将电子汇集到共享电子对中，两个原子核都被同一对电子吸引，从而有效地满足八隅体规则（氢则满足双电子规则）。
2. Formation of Covalent Bonds | 共价键的形成
When two non-metal atoms approach each other, their outer electron shells begin to overlap. Each atom donates one electron to form a shared pair, which then orbits around both nuclei. The electrostatic attraction between the positively charged nuclei and the negatively charged shared pair of electrons holds the atoms tightly together.
当两个非金属原子相互靠近时，它们的外层电子壳开始重叠。每个原子提供一个电子形成共享对，该共享对随后围绕两个原子核运动。带正电的原子核与带负电的共享电子对之间的静电吸引力将两个原子紧紧结合在一起。
The formation of a covalent bond results in a lower overall energy, making the molecule more stable than the separate atoms. The shared pair is localised between the two nuclei, which is why covalent bonds are directional – they hold specific atoms together in a fixed arrangement.
共价键的形成会导致体系总能量降低，因此分子比分离的原子更稳定。共享的电子对定域在两个原子核之间，这就是共价键具有方向性的原因——它们以固定的排列方式把特定的原子连接在一起。
3. Single Covalent Bonds | 单共价键
A single covalent bond involves one shared pair of electrons, represented by a single line in displayed formulae. Many simple molecules contain only single bonds. Common examples include hydrogen (H-H), chlorine (Cl-Cl), water (H₂O), methane (CH₄) and ammonia (NH₃).
单共价键包含一对共享电子，在展示式中用一条短横线表示。许多简单分子仅含有单键，常见例子包括氢气（H-H）、氯气（Cl-Cl）、水（H₂O）、甲烷（CH₄）和氨（NH₃）。
In methane, the carbon atom forms four single covalent bonds with four hydrogen atoms. Carbon has four outer electrons and needs four more to complete its octet, while each hydrogen atom needs one more electron to achieve the stable duet. By sharing one electron each, all atoms reach a stable configuration.
在甲烷中，碳原子与四个氢原子形成四个单共价键。碳原子有四个外层电子，还需要四个来填满八隅体，而每个氢原子需要一个电子来实现稳定的双电子结构。通过各自提供一个电子，所有原子都达到了稳定构型。
4. Double and Triple Bonds | 双键与叁键
When two pairs of electrons are shared between two atoms, a double covalent bond forms. This is represented by two lines ( = ) in displayed formulae. Carbon dioxide (O=C=O) and oxygen gas (O=O) contain double bonds.
当两个原子之间共享两对电子时，就形成了双共价键，在展示式中用两条短线（=）表示。二氧化碳（O=C=O）和氧气（O=O）都含有双键。
A triple covalent bond arises when three pairs of electrons are shared, represented by three lines ( ≡ ). The most important example is nitrogen gas, N₂ (N≡N), where each nitrogen atom contributes three electrons to complete its octet. Triple bonds are very strong and require a large amount of energy to break.
当两个原子之间共享三对电子时，就形成了叁共价键，用三条短线（≡）表示。最重要的例子是氮气 N₂（N≡N），每个氮原子提供三个电子以完成八隅体。叁键非常强，断裂需要大量能量。
5. Dot-and-Cross Diagrams | 点叉图
Dot-and-cross diagrams are a way to model the outer electrons of atoms in a molecule and show which electrons are shared in covalent bonds. Electrons from one atom are drawn as dots ( • ), while electrons from the other atom are drawn as crosses ( × ), ensuring the origin of each shared electron is clear.
点叉图是一种表示分子中原子外层电子以及哪些电子在共价键中被共享的模型。来自一个原子的电子画成点（•），来自另一个原子的电子画成叉（×），这样可以清楚地看出每个共享电子的来源。
For example, in a dot-and-cross diagram of water (H₂O), the oxygen atom provides six valence electrons (dots) and each hydrogen provides one electron (crosses). Two bonding pairs form between O and each H, while the oxygen atom also has two lone pairs of electrons that are not involved in bonding.
例如，在水（H₂O）的点叉图中，氧原子提供六个价电子（点），每个氢原子提供一个电子（叉）。氧与每个氢之间形成一个键合电子对，同时氧原子还有两对未参与成键的孤电子对。
You must be able to draw dot-and-cross diagrams for molecules such as H₂, Cl₂, HCl, H₂O, NH₃, CH₄, O₂, N₂ and CO₂. In an exam, always remember to draw the outer shells as overlapping circles and show all electrons, including lone pairs.
你必须能够画出 H₂、Cl₂、HCl、H₂O、NH₃、CH₄、O₂、N₂ 和 CO₂ 等分子的点叉图。在考试中，记得要画出重叠的外层电子壳圆圈，并标出所有电子，包括孤对电子。
6. Molecular Formulae and Displayed Formulae | 分子式与展示式
A molecular formula tells you the actual number of atoms of each element in a molecule, for example H₂O for water. A displayed formula (or structural formula) shows all the atoms and the covalent bonds between them using lines, helping to show exactly how the atoms are connected.
分子式告诉你分子中各元素原子的实际数量，例如水的分子式是 H₂O。展示式（或结构式）则用线段显示出所有原子以及它们之间的共价键，有助于看清原子之间的确切连接方式。
For a molecule like ethanol (C₂H₅OH), the displayed formula would show all C–C, C–H, C–O and O–H bonds. Displayed formulae are particularly useful when identifying functional groups in organic chemistry.
对于像乙醇（C₂H₅OH）这样的分子，展示式会显示出所有的 C–C、C–H、C–O 和 O–H 键。在有机化学中识别官能团时，展示式尤其有用。
Covalent bonds are also sometimes represented using 3D models, such as ball-and-stick or space-filling models, to illustrate bond angles and molecular geometry. However, for GCSE OCR Chemistry, mastering dot-and-cross and displayed formulae is the primary requirement.
共价键有时也用三维模型来表示，如球棍模型或空间填充模型，以展示键角和分子的几何形状。不过，对于 GCSE OCR 化学，掌握点叉图和展示式是主要要求。
7. Properties of Simple Covalent Molecules | 简单共价分子的性质
Substances made of simple covalent molecules, such as water, carbon dioxide, chlorine and methane, have relatively low melting and boiling points. This is because the covalent bonds within each molecule are strong, but the intermolecular forces between molecules are weak and require little energy to overcome.
由简单共价分子组成的物质，如水、二氧化碳、氯气和甲烷，熔点和沸点相对较低。这是因为每个分子内部的共价键很强，但分子之间的分子间力很弱，克服这些力只需很少的能量。
Most simple molecular substances are gases or liquids at room temperature. They do not conduct electricity because they have no free charged particles – no ions or delocalised electrons – even when molten or dissolved in water (unless they react with water to form ions, as HCl does).
大多数简单分子物质在室温下是气体或液体。它们不导电，因为既没有离子也没有离域电子——无论是在熔融状态还是溶解在水中（除非它们与水反应生成离子，如 HCl）。
Although covalent bonds within the molecules are very strong, the overall structure is held together only by weak intermolecular forces, sometimes called van der Waals’ forces. This explains why small covalent molecules are often volatile and have low viscosity.
尽管分子内部的共价键非常强，但整个结构仅靠微弱的分子间力（有时称为范德华力）维系。这就解释了为什么小共价分子往往易挥发且粘度低。
8. Giant Covalent Structures | 巨型共价结构
In some substances, billions of atoms are joined together by covalent bonds in a continuous three-dimensional network. These are called giant covalent structures or macromolecules. They have very high melting and boiling points because strong covalent bonds must be broken throughout the whole lattice for the substance to melt or boil.
在某些物质中，数亿个原子通过共价键连接成一个连续的三维网络。这些被称为巨型共价结构或大分子。它们的熔点和沸点非常高，因为要使物质熔化或沸腾就必须破坏整个晶格中大量的强共价键。
Unlike simple molecules, giant covalent structures are typically hard, often insoluble in water, and (with the exception of graphite) do not conduct electricity. Examples include diamond, graphite, silicon dioxide (silica), and newer carbon allotropes like graphene.
与简单分子不同，巨型共价结构通常很硬，往往不溶于水，并且（除石墨外）不导电。例子包括金刚石、石墨、二氧化硅（硅石）以及像石墨烯这样的新型碳同素异形体。
9. Diamond | 金刚石
Diamond is a form of carbon where each carbon atom forms four strong single covalent bonds with four other carbon atoms in a tetrahedral arrangement. This rigid three-dimensional giant covalent lattice makes diamond the hardest known natural substance.
金刚石是碳的一种形式，每个碳原子以正四面体的方式与另外四个碳原子形成四个坚固的单共价键。这种刚性的三维巨型共价晶格使金刚石成为已知最硬的天然物质。
Because all four of each carbon’s outer electrons are used in bonding, there are no delocalised electrons or free ions. Diamond therefore cannot conduct electricity – it is an excellent electrical insulator. However, it is an exceptional thermal conductor due to its tightly bonded rigid lattice which transmits vibrations efficiently.
由于每个碳原子的四个外层电子全部用于成键，没有离域电子或自由离子，因此金刚石不能导电——它是一种优良的电绝缘体。但由于其紧密成键的刚性晶格能高效传递振动，金刚石是非常好的导热体。
Diamond also has a very high refractive index and is extremely transparent, which makes it prized both in jewellery and in industrial cutting and drilling tools.
金刚石还具有很高的折射率并且极为透明，因此在珠宝和工业切割及钻探工具中都备受珍视。
10. Graphite | 石墨
Graphite is another giant covalent allotrope of carbon, but its structure is very different from diamond. Each carbon atom forms three strong covalent bonds with three other carbon atoms, creating flat hexagonal layers. The fourth outer electron becomes delocalised and is free to move between the layers.
石墨是碳的另一种巨型共价同素异形体，但其结构与金刚石截然不同。每个碳原子与另外三个碳原子形成三个强共价键，构成扁平的六边形层状结构。第四个外层电子离域，可以自由地在层间移动。
These delocalised electrons allow graphite to conduct electricity along the planes, which is why it is used in electrodes and as a solid lubricant in situations where high temperatures would break down oil-based lubricants. The layers themselves are held together only by weak intermolecular forces, allowing them to slide over each other easily – giving graphite its slippery feel.
这些离域电子使石墨可以沿层平面导电，这就是它被用于电极和在高温下替代润滑油作为固体润滑剂的原因。层与层之间仅靠微弱的分子间力结合，因此可以轻易地相互滑动——这赋予了石墨滑腻的手感。
Like diamond, graphite has a very high melting point because covalent bonds within each layer must be broken to melt it. However, it is softer and more flexible than diamond due to its layered structure.
和金刚石一样，石墨的熔点非常高，因为要熔化它就必须破坏每一层内的共价键。然而，由于其层状结构，石墨比金刚石更软且更具柔韧性。
11. Silicon Dioxide (Silica) | 二氧化硅
Silicon dioxide, commonly known as silica, has a giant covalent structure similar to diamond but with a key difference: instead of carbon atoms, the structure contains both silicon and oxygen atoms. Each silicon atom is covalently bonded to four oxygen atoms, and each oxygen atom is bonded to two silicon atoms, forming a continuous SiO₂ network.
二氧化硅，通常称为硅石，具有与金刚石类似的巨型共价结构，但有一个关键区别：其结构中不是碳原子，而是同时包含硅和氧原子。每个硅原子与四个氧原子形成共价键，每个氧原子又与两个硅原子成键，构成连续的 SiO₂ 网络。
Because of this extensive covalent bonding, silica has a very high melting point (around 1710 °C) and is very hard. It is found naturally as quartz and in sand. It does not conduct electricity, as all electrons are held tightly in covalent bonds or lone pairs.
由于这种广泛的共价键，二氧化硅的熔点非常高（约 1710 °C），并且十分坚硬。它天然以石英和砂子的形式存在。它不导电，因为所有电子都牢牢地固定在共价键或孤对电子中。
Silica is a crucial raw material for making glass and ceramics, and it is also used in the electronics industry due to its insulating properties and its role in producing silicon chips.
二氧化硅是制造玻璃和陶瓷的关键原料，也因其绝缘性能以及在制造硅芯片中的作用而被用于电子工业。
12. Graphene and Fullerenes | 石墨烯与富勒烯
Graphene is a single layer of graphite – a two-dimensional sheet of carbon atoms arranged in hexagons, just one atom thick. It is extremely strong (about 200 times stronger than steel), transparent, and an excellent conductor of electricity because of its delocalised electrons. These properties make it a potentially revolutionary material for flexible electronics, composite materials, and desalination membranes.
石墨烯是单层石墨——一个由碳原子按六边形排列而成的二维薄片，厚度仅为一个原子。它极其坚固（强度约为钢的 200 倍），透明，并因具有离域电子而成为优良的导电体。这些特性使其在柔性电子器件、复合材料和海水淡化膜等领域具有潜在的革命性应用前景。
Fullerenes are molecules of carbon shaped like hollow spheres or tubes. The most famous is buckminsterfullerene (C₆₀), consisting of 60 carbon atoms arranged in a pattern of hexagons and pentagons, resembling a football. Fullerenes have uses in drug delivery, catalysts, and lubricants because they can encase other molecules inside their hollow cage.
富勒烯是形状类似中空球体或管子的碳分子。最著名的是巴克敏斯特富勒烯（C₆₀），由 60 个碳原子以六边形和五边形模式排列而成，形似足球。富勒烯可用于药物递送、催化剂和润滑剂，因为它们能将其他分子包覆在其空心笼状结构内。
Carbon nanotubes are cylindrical fullerenes with exceptional tensile strength and electrical conductivity, and they are used in high-performance sports equipment, miniature transistors, and medical devices. Both graphene and fullerenes highlight the versatility of carbon’s covalent bonding.
碳纳米管是圆柱形的富勒烯，具有卓越的抗拉强度和导电性，可用于高性能运动器材、微型晶体管和医疗设备。石墨烯和富勒烯都凸显了碳元素共价键的多样性。
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