Types of Chemical Bonding | 化学键类型

📚 Types of Chemical Bonding | 化学键类型

Chemical bonding is the central idea that explains how atoms and ions combine to form the thousands of substances around us. In Cambridge A-Level Chemistry, you need to understand ionic, covalent and metallic bonding, as well as dative covalent bonds, bond polarity, sigma and pi bonds, and how bonding controls physical properties.

化学键是解释原子和离子如何结合形成我们周围成千上万种物质的核心概念。在剑桥A-Level化学中，你需要理解离子键、共价键和金属键，还要掌握配位共价键、键的极性、σ键和π键，以及化学键如何决定物理性质。

---

1. What is a Chemical Bond? | 什么是化学键？

A chemical bond is an electrostatic attraction that holds atoms or ions together. Atoms form bonds because the bonded arrangement has lower energy and is therefore more stable than separate atoms.

化学键是使原子或离子结合在一起的静电吸引力。原子形成化学键是因为成键后的体系能量更低，因此比单独的原子更稳定。

The three principal types of chemical bonding are ionic bonding, covalent bonding and metallic bonding. In addition, Cambridge A-Level requires you to describe dative covalent bonding as a special case of covalent bonding, and to distinguish sigma and pi bonds in multiple bonds.

化学键的三种主要类型是离子键、共价键和金属键。此外，剑桥A-Level要求你能够把配位共价键描述为共价键的一种特殊情况，并区分多重键中的σ键和π键。

Bonding type is determined by the elements involved and the difference in electronegativity between them. Metals tend to lose electrons, non-metals tend to gain electrons, and two non-metals tend to share electrons.

键的类型由所涉及的元素以及它们之间电负性的差值决定。金属倾向于失去电子，非金属倾向于获得电子，而两个非金属之间倾向于共享电子。

---

2. Ionic Bonding | 离子键

Ionic bonding occurs between a metal and a non-metal. Electrons are transferred from the metal atom to the non-metal atom, forming positive cations and negative anions. The oppositely charged ions are held together by strong electrostatic attraction in a giant ionic lattice.

离子键通常形成于金属与非金属之间。电子从金属原子转移给非金属原子，形成带正电的阳离子和带负电的阴离子。这些带相反电荷的离子通过强烈的静电吸引力结合在巨型离子晶格中。

For example, in sodium chloride, each sodium atom loses one electron and each chlorine atom gains one electron:

例如，在氯化钠中，每个钠原子失去一个电子，每个氯原子得到一个电子：

Na → Na⁺ + e⁻

Cl + e⁻ → Cl⁻

The resulting Na⁺ and Cl⁻ ions attract each other to form the NaCl lattice. The formula of an ionic compound shows the simplest ratio of ions, for example MgO, Na₂O and MgCl₂.

生成的 Na⁺ 和 Cl⁻ 相互吸引形成 NaCl 晶格。离子化合物的化学式表示离子的最简整数比，例如 MgO、Na₂O 和 MgCl₂。

Ionic compounds have high melting and boiling points because the electrostatic forces between oppositely charged ions are strong and extend throughout the lattice. They conduct electricity only when molten or dissolved in water, because the ions become free to move as charge carriers.

离子化合物具有较高的熔点和沸点，因为相反电荷离子之间的静电作用力很强，并且遍布整个晶格。它们只有在熔融或溶于水时才导电，因为此时离子可以自由移动并充当载流子。

---

3. Covalent Bonding | 共价键

Covalent bonding occurs between two non-metal atoms. The atoms share one or more pairs of electrons so that each atom can achieve a stable outer electron configuration.

共价键形成于两个非金属原子之间。原子共享一对或多对电子，使每个原子都能达到稳定的外层电子构型。

A single covalent bond involves one shared pair of electrons, a double bond involves two shared pairs, and a triple bond involves three shared pairs. Common examples include H₂, Cl₂, O₂, N₂, CH₄ and CO₂.

单键涉及一对共享电子，双键涉及两对共享电子，三键涉及三对共享电子。常见的例子包括 H₂、Cl₂、O₂、N₂、CH₄ 和 CO₂。

Covalent bonding can produce simple molecules such as water and carbon dioxide, or giant covalent structures such as diamond, graphite and silicon dioxide. Simple molecules have strong covalent bonds within the molecule but weak intermolecular forces between molecules.

共价键可以形成简单分子，例如水和二氧化碳，也可以形成巨型共价结构，例如金刚石、石墨和二氧化硅。简单分子内部的共价键很强，但分子之间的分子间作用力很弱。

In a dot-and-cross diagram, only outer-shell electrons are shown. A line between two atoms represents one shared pair of electrons.

在电子式和电子点叉图中，只画最外层电子。两个原子之间的一条线表示一对共享电子。

---

4. Dative Covalent Bonding | 配位共价键

A dative covalent bond, also called a coordinate bond, is a covalent bond in which both electrons in the shared pair come from the same atom. Once formed, a dative covalent bond is identical to an ordinary covalent bond.

配位共价键，也叫配位键，是一种共价键，其中共享电子对中的两个电子都来自同一个原子。一旦形成，配位共价键与普通共价键完全相同。

The atom that donates the pair must have a lone pair of electrons, and the accepting atom must have an empty orbital. A classic example is the formation of the ammonium ion:

提供电子对的原子必须具有孤对电子，接受电子的原子必须具有空轨道。一个典型的例子是铵离子的形成：

NH₃ + H⁺ → NH₄⁺

In this reaction, the nitrogen atom in ammonia donates its lone pair to the hydrogen ion, forming a new N–H bond in which both electrons come from nitrogen.

在这个反应中，氨分子中的氮原子把孤对电子提供给氢离子，形成一个新的 N–H 键，该键中的两个电子都来自氮原子。

Other examples include the hydronium ion H₃O⁺, formed when water donates a lone pair to H⁺, and carbon monoxide CO, in which a dative bond is present alongside normal covalent bonding.

其他例子包括水分子把一个孤对电子提供给 H⁺ 形成的水合氢离子 H₃O⁺，以及一氧化碳 CO，其中既存在普通共价键，也存在配位键。

---

5. Metallic Bonding | 金属键

Metallic bonding occurs in metals and alloys. Metal atoms release their outer-shell electrons, forming a regular lattice of positive metal cations surrounded by a sea of delocalised electrons.

金属键存在于金属和合金中。金属原子释放其外层电子，形成排列规则的正金属阳离子晶格，周围被离域电子的“海洋”所包围。

The electrostatic attraction between the positive metal ions and the delocalised electrons holds the metal together. This model explains the key properties of metals.

正金属离子与离域电子之间的静电吸引力把金属结合在一起。这个模型可以解释金属的关键性质。

Mg → Mg²⁺ + 2e⁻

Metals conduct electricity in both solid and liquid states because the delocalised electrons are free to move throughout the structure. Metals are malleable and ductile because layers of cations can slide over one another without breaking the metallic bonding.

金属在固态和液态下都能导电，因为离域电子可以在整个结构中自由移动。金属具有延展性和展性，因为阳离子层可以在不破坏金属键的情况下相互滑动。

The strength of metallic bonding increases with greater positive charge on the metal cation and with smaller ionic radius. This explains why melting points generally increase from Group 1 to Group 3 metals and across transition metals.

金属键的强度随着金属阳离子正电荷的增加和离子半径的减小而增强。这就解释了为什么从第1族到第3族金属以及过渡金属的熔点总体上会升高。

---

6. Electronegativity and Bond Polarity | 电负性与键的极性

Electronegativity is the ability of an atom to attract the bonding pair of electrons in a covalent bond. Fluorine is the most electronegative element, and electronegativity generally increases across a period and decreases down a group.

电负性是原子在共价键中吸引成键电子对的能力。氟是电负性最大的元素，电负性通常在同一周期从左到右增大，在同一族从上到下减小。

When two atoms in a covalent bond have different electronegativities, the electron pair is pulled closer to the more electronegative atom. This creates a polar covalent bond with partial charges.

当成键的两个原子电负性不同时，电子对会被拉向电负性较大的原子。这就产生了带有部分电荷的极性共价键。

For example, in hydrogen chloride, chlorine is more electronegative than hydrogen, so chlorine develops a partial negative charge δ⁻ and hydrogen develops a partial positive charge δ⁺.

例如，在氯化氢中，氯的电负性大于氢，因此氯带部分负电荷 δ⁻，氢带部分正电荷 δ⁺。

H–Cl → H δ⁺ – Cl δ⁻

If the electronegativity difference is very small, the bond is non-polar. If it is moderate, the bond is polar covalent. If it is very large, generally above about 1.7, the bond tends to be ionic.

如果电负性差值很小，则键是非极性的；如果差值适中，则为极性共价键；如果差值很大，通常大于约 1.7，则倾向于形成离子键。

---

7. Sigma and Pi Bonds | σ键与π键

A sigma bond, written as σ, is formed by head-on overlap of atomic orbitals along the line joining the two nuclei. Sigma bonds can form from s-s, s-p or p-p orbital overlap.

σ键是由原子轨道沿着连接两个原子核的直线方向进行头对头重叠形成的。σ键可以由 s-s、s-p 或 p-p 轨道重叠形成。

A pi bond, written as π, is formed by sideways overlap of p orbitals above and below the line between two nuclei. Pi bonds are only found in double and triple bonds.

π键是由 p 轨道在原子核连线上下方进行侧向重叠形成的。π键只存在于双键和三键中。

A single bond is a σ bond. A double bond contains one σ bond and one π bond. A triple bond contains one σ bond and two π bonds.

单键是一个 σ 键；双键包含一个 σ 键和一个 π 键；三键包含一个 σ 键和两个 π 键。

Because pi bonds involve sideways overlap, they are weaker than sigma bonds and they restrict rotation around the double bond. This has important consequences for geometric isomerism in alkenes.

由于 π 键涉及侧向重叠，它比 σ 键弱，并且会限制双键周围的旋转。这对烯烃的几何异构现象有重要影响。

---

8. Bond Length and Bond Strength | 键长与键能

Bond length is the average distance between the nuclei of two bonded atoms. Bond energy, also called bond enthalpy, is the energy required to break one mole of a particular bond in the gaseous state.

键长是两个成键原子核之间的平均距离。键能，也叫键焓，是在气态下破坏 1 摩尔某种特定化学键所需的能量。

Multiple bonds are shorter and stronger than single bonds. For carbon-carbon bonds, typical values are:

多重键比单键更短、更强。对于碳碳键，典型数值如下：

Bond	Type	Bond length / pm	Bond energy / kJ mol⁻¹
C–C	single	154	348
C=C	double	134	614
C≡C	triple	120	839

Short bonds have greater bond energy and are stronger. This trend is useful when comparing the reactivity of alkanes, alkenes and alkynes.

较短的键具有较大的键能，也更牢固。这个规律在比较烷烃、烯烃和炔烃的反应活性时非常有用。

Bond polarity also affects bond strength: polar bonds often have additional electrostatic attraction that can make them stronger than expected from covalent bonding alone.

键的极性也会影响键的强度：极性键通常具有额外的静电吸引力，因此可能比单纯共价键预期的更强。

---

9. Intermolecular Forces vs Chemical Bonds | 分子间作用力与化学键的区别

Intermolecular forces are not chemical bonds. They are weak electrostatic attractions between separate molecules, whereas chemical bonds act within a molecule, ion or lattice.

分子间作用力不是化学键。它们是不同分子之间较弱的静电吸引力，而化学键作用于分子、离子或晶格内部。

The three main types of intermolecular force are London dispersion forces, permanent dipole-dipole forces and hydrogen bonding. London forces exist between all molecules and increase with molecular size and surface contact.

分子间作用力主要有三种类型：伦敦色散力、永久偶极-偶极力和氢键。伦敦色散力存在于所有分子之间，并随分子大小和接触面积增大而增强。

Hydrogen bonding is the strongest intermolecular force. It occurs when a hydrogen atom is covalently bonded to a highly electronegative atom with a lone pair, such as nitrogen, oxygen or fluorine, and is attracted to a lone pair on a neighbouring molecule.

氢键是最强的分子间作用力。当氢原子与具有孤对电子的强电负性原子（如氮、氧或氟）形成共价键，并被邻近分子上的孤对电子吸引时，就产生氢键。

Because intermolecular forces are much weaker than covalent, ionic or metallic bonds, simple molecular substances have much lower melting and boiling points than giant structures.

由于分子间作用力远弱于共价键、离子键或金属键，简单分子物质的熔点和沸点远低于

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）