定义Definition
化学键是使原子或离子结合在一起的强相互作用，主要有离子键、共价键和金属键三类。化学反应的本质是旧化学键断裂和新化学键形成。分子之间的范德华力和氢键比化学键弱得多，一般不称为化学键。
A chemical bond is a strong attraction holding atoms or ions together; the main types are ionic, covalent and metallic. A chemical reaction breaks old bonds and forms new ones. Van der Waals forces and hydrogen bonds between molecules are much weaker and are not usually called chemical bonds.
三种主要类型The three main types
离子键：阴、阳离子间的静电吸引，如 NaCl；共价键：原子间共用电子对，如 H₂、H₂O；金属键：金属阳离子与离域电子“海”之间的吸引，如 Cu、Na。
Ionic bonding: electrostatic attraction between oppositely charged ions, as in NaCl. Covalent bonding: shared electron pairs between atoms, as in H₂ and H₂O. Metallic bonding: attraction between metal cations and a 'sea' of delocalised electrons, as in Cu and Na.
键型是连续变化的A continuum of bond types
两原子电负性差越大，键的离子性越强：H–H 是纯共价键，H–Cl 是极性共价键，NaCl 主要为离子键。许多化合物介于两者之间，如 AlCl₃ 的键具有明显共价性。
The greater the electronegativity difference, the more ionic the bond: H–H is purely covalent, H–Cl is polar covalent and NaCl mainly ionic. Many compounds lie in between; the bonds in AlCl₃ have considerable covalent character.
年表Timeline
- 1916
路易斯提出共价键是共用电子对
Lewis describes the covalent bond as a shared electron pair
- 1939
鲍林出版《化学键的本质》
Pauling publishes The Nature of the Chemical Bond