📚 IB Chemistry: Types of Chemical Bonds and Bonding Principles | IB化学：化学键类型与成键原理
Chemical bonding is the foundation of chemistry: it explains why atoms group together to form molecules and compounds, and how the resulting structure determines the physical and chemical properties of matter. In IB Chemistry (Topic 4 and the higher-level extensions in Topic 14), you need to master not only the classification of bonds – ionic, covalent and metallic – but also the underlying principles of electron transfer, electron sharing and electrostatic attraction. This article breaks down the key concepts, common calculations and exam traps, so you can approach bonding questions with clarity and confidence.
化学键是化学的基石：它解释了原子为何聚集形成分子和化合物，以及由此产生的结构如何决定物质的物理和化学性质。在 IB 化学（Topic 4 及 Topic 14 的 HL 拓展内容）中，你不仅要掌握化学键的分类——离子键、共价键和金属键，还要理解电子转移、电子共享和静电吸引背后的原理。本文将拆解核心概念、常见计算和考试陷阱，帮助你清晰、自信地应对成键类题目。
1. Why Atoms Bond: The Octet Rule and Stability | 原子为何成键：八隅体规则与稳定性
Atoms bond because the bonded state has lower potential energy than the separated atoms. During bond formation, energy is released (exothermic), making the system more stable. The octet rule states that main-group atoms tend to gain, lose or share electrons so as to achieve a full outer shell of eight electrons (or two electrons for hydrogen and helium), matching the electron configuration of a noble gas.
原子之所以成键，是因为成键态的能量比孤立原子更低。在成键过程中会释放能量（放热），从而使体系更加稳定。八隅体规则指出：主族原子倾向于通过得到、失去或共享电子来获得 8 个电子的满外层（氢和氦为 2 个电子），从而与稀有气体的电子构型一致。
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Only the valence electrons take part in chemical bonding; core electrons remain unchanged.
只有价电子参与化学键；内层电子保持不变。
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The idea of a stable electron arrangement helps predict common ion charges, such as Na⁺, Mg²⁺, O²⁻ and Cl⁻.
“稳定电子排布”的观念有助于预测常见离子电荷，如 Na⁺、Mg²⁺、O²⁻ 和 Cl⁻。
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There are important exceptions to the octet rule (Be, B, expanded octets), discussed in Section 7.
八隅体规则存在重要例外（Be、B、膨胀八隅体），详见第 7 节。
2. Ionic Bonding: Electrostatic Attraction and Lattice Enthalpy | 离子键：静电吸引与晶格焓
Ionic bonding occurs when a metal transfers one or more electrons to a non-metal, producing positive cations and negative anions. The ionic bond is the strong electrostatic attraction between oppositely charged ions. This type of bond is typically observed for elements with a large electronegativity difference, usually greater than 1.8 on the Pauling scale.
离子键发生在金属将电子转移给非金属时，生成正离子（阳离子）和负离子（阴离子）。离子键的本质是带有相反电荷的离子之间的强烈静电吸引。这种键通常出现在电负性差值较大的元素之间，在鲍林标度上一般大于 1.8。
Na(g) → Na⁺(g) + e⁻
Cl(g) + e⁻ → Cl⁻(g)
Na⁺(g) + Cl⁻(g) → NaCl(s) ΔH < 0
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Ionic compounds have high melting and boiling points because the electrostatic forces between ions are strong.
离子化合物的熔点和沸点较高，因为离子间的静电作用力很强。
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They conduct electricity when molten or dissolved in water, because the ions are free to move; in the solid state they do not conduct.
它们在熔融或溶于水时能导电，因为离子可以自由移动；固态时不导电。
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Lattice enthalpy is the energy released when one mole of an ionic solid is formed from its gaseous ions. Smaller ions with higher charges give more negative lattice enthalpies and stronger ionic bonds.
晶格焓是指由气态离子形成 1 mol 离子固体时所释放的能量。离子越小、电荷越高，晶格焓越负，离子键越强。
3. Covalent Bonding: Sharing Electron Pairs | 共价键：共享电子对
Covalent bonding involves the sharing of at least one pair of electrons between two non-metal atoms. Each shared pair constitutes a single covalent bond. The shared electrons are localised in the region between the two nuclei, and the attraction between these electrons and both nuclei holds the molecule together.
共价键是指两个非金属原子之间共享至少一对电子。每一对共享电子构成一个共价单键。共享电子被定域在两个原子核之间的区域，这些电子与两个原子核之间的吸引使分子保持稳定。
H· + H· → H—H
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Single bonds involve one shared pair; double bonds involve two shared pairs; triple bonds involve three shared pairs.
单键含有一对共享电子；双键含有两对；三键含有三对。
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Covalent bonds are directional, which gives rise to specific molecular shapes and bond angles.
共价键具有方向性，因此分子具有特定的空间构型和键角。
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Common examples include diatomic molecules: H₂, O₂, N₂, Cl₂ and so on.
常见例子包括双原子分子：H₂、O₂、N₂、Cl₂ 等。
4. Dative Covalent (Coordinate) Bonds | 配位共价键
In a dative covalent bond, sometimes called a coordinate bond, both electrons in the shared pair come from the same atom. The donor atom must have a lone pair of electrons, and the acceptor atom must have an empty orbital. An arrow is often used to show the direction of donation: A → B.
配位共价键又称坐标键，是指共享电子对中的两个电子都来自同一个原子。给出电子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。通常用箭头表示电子对给予的方向：A → B。
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In NH₄⁺, the lone pair on NH₃ donates to an H⁺ ion.
在 NH₄⁺ 中，NH₃ 上的孤对电子提供给 H⁺。
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In H₃O⁺, the lone pair on H₂O donates to an H⁺ ion.
在 H₃O⁺ 中，H₂O 上的孤对电子提供给 H⁺。
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In H₃N→BF₃, the lone pair on NH₃ is donated to the boron atom in BF₃, because boron has only six valence electrons.
在 H₃N→BF₃ 中，NH₃ 的孤对电子提供给 BF₃ 中的硼原子，因为硼只有 6 个价电子。
Once formed, a dative covalent bond is indistinguishable from a regular covalent bond; its strength and length are essentially the same.
配位共价键一旦形成，便与普通共价键无法区分；其键长和键能基本相同。
5. Metallic Bonding: The Sea of Electrons | 金属键：电子海
Metallic bonding occurs between metal atoms. The valence electrons are delocalised, meaning they move freely throughout the metal lattice. The strong electrostatic attraction between the positive metal ions and the delocalised electrons, often described as a “sea of electrons”, constitutes the metallic bond.
金属键发生在金属原子之间。价电子发生离域，可以在整个金属晶格中自由移动。正金属离子与离域电子（常称为“电子海”）之间的强烈静电吸引构成了金属键。
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Metals conduct electricity and heat well because the delocalised electrons carry charge and thermal energy.
金属导电和导热良好，因为离域电子能携带电荷和
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