化学键(bonding)

使原子缔合成分子、离子、晶体、金属及其他稳定物质形式的相互作用。一些原子相互接近时，它们的原子核和电子发生相互作用，并有使自己的空间排列方式的总能量小於任何其他排列方式的趋势。如果一个原子团的总能量小於其各组分原子的能量之和，则它们是化学键合的，而所减小的能量就是键能。一个原子可形成的键数，称为原子价或原子价数。一个原子的原子价正好是其价电子壳层（即最外电子壳层）中的不成对电子数。共价键形成分子：原子和其他特定原子间藉共享一对电子而结合。如果共享平均，这个分子就没有极性，如果不平均，这个分子就是电偶极。离子键是共享极不平均的结果：阳离子放弃电子，阴离子拾起电子，所有的离子藉着静电力结合成晶体。在晶体金属中，一个分散的电子把键分给原子共享（金属键）。其他形式包括氢键；芳香族化合物的键；配位共价键；多中心键，以硼烷为例，其中有两个原子以上共享电子对；配位复合体中的键至今仍少有人了解。亦请参阅van der Waals forces。

English version：

bonding

Any of the interactions that account for the association of atoms into molecules, ions, crystals, metals, and other stable species. When atoms' nuclei and electrons interact, they tend to distribute themselves so that the total energy is lowest; if the energy of a group arrangement is lower than the sum of the components' energies, they bond. The physics and mathematics of bonding were developed as part of quantum mechanics. The number of bonds an atom can form, its valence, equals the number of electrons it contributes or receives. Covalent bonds form molecules: Atoms bond to specific other atoms by sharing an electron pair between them. If the sharing is even, the molecule is not polar; if it is uneven, the molecule is an electric dipole. Ionic bonds are the extreme of uneven sharing: Cations give up electrons, anions take them up, and all the ions are held together in a crystal by electrostatic forces. In crystalline metals, a diffuse electron sharing bonds the atoms (metallic bonding). Other types include hydrogen bonding; bonds in aromatic compounds; coordinate covalent bonds; multicenter bonds, exemplified by boranes (boron hydrides), in which more than two atoms share electron pairs; and the bonds in coordination complexes (see transition element), still poorly understood. See also van der Waals forces.

参考文章

• 化学键Bond，Chemical地球科学