价键理论(VB)与分子轨道理论(MO)是研究分子体系的两种量子力学方法.它是历史上最早发展起来的处理多个化学键分子的量子力学理论.
- 价键理论对于分子定态的性质（键长，键角等）的解释和分子轨道理论相近
- 分子轨道理论在研究和电子激发相关的性质时（分子颜色，光电子能谱等）更为有效
价键理论 (Valence bond theory, VB, 又称电子配对理论)
- lewis理论: 提出化学键、lewis结构式的概念，八隅体规则
- Heitler和London继承了Lewis共用电子对的概念，以QM为基础，原子轨道重叠（原子核间电子概率密度大，吸引原子核而成键），如$\sigma$键（原子轨道延核间连线fang，同号重叠，即头碰头）、$\pi$键（两原子轨道垂直核间连线相互平行，同号重叠，即肩并肩）、配位键（成键原子一方有孤对电子，另一方有空轨道）
- Pauling提出杂化轨道理论，推广了Heilter-London理论: 形成分子的过程中，若干不同类型能量相近的原子轨道重新组成成一组新轨道，这种重新组合的过程称为杂化，所形成的新轨道叫杂化轨道.可参考史上最易理解杂化轨道理论(图解）.
- 价层电子互斥理论 (Valence Shell Electron Pair Repulsion, VSEPR)
分子轨道理论 (Molecular orbital theory, MO)
- VB理论用原子轨道的重组杂化成键来理解化学，而MO理论则注重于分子轨道的了解，即认为分子中的电子围绕整个分子运动(electrons in a molecule are not assigned to individual chemical bonds between atoms, but are treated as moving under the influence of the atomic nuclei in the whole molecule).
- 计算化学中常以原子轨道线性组合近似来计算分子轨道波函数.简单地讲，该方法意即，分子轨道由原子轨道的线性组合(linear combination of atomic orbitals, LACO)而成.原子轨道波函数各乘以某一系数相加或相减，得到分子轨道波函数.组合时原子轨道对分子轨道的贡献体现在系数上，组合前后轨道总数不变.
- 键级B.O=1/2(成键电子书-反键电子数)
晶体场理论 (Crystal field theory, CFT)
- Crystal field theory (CFT) describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution (anion neighbors).
- CFT successfully accounts for some magnetic properties, colors, hydration enthalpies, and spinel structures of transition metal complexes, but it does not attempt to describe bonding.
- CFT was subsequently combined with molecular orbital theory to form the more realistic and complex ligand field theory (LFT), which delivers insight into the process of chemical bonding in transition metal complexes.
配位场力场 (Ligand field theory, LFT)
- Ligand field theory (LFT) describes the bonding, orbital arrangement, and other characteristics of coordination complexes.
- Ligand field theory resulted from combining the principles laid out in molecular orbital theory and crystal field theory, which describes the loss of degeneracy of metal d orbitals in transition metal complexes.
- It represents an application of molecular orbital theory to transition metal complexes. A transition metal ion has nine valence atomic orbitals - consisting of five nd, one (n+1)s, and three (n+1)p orbitals. These orbitals are of appropriate energy to form bonding interaction with ligands. The LFT analysis is highly dependent on the geometry of the complex, but most explanations begin by describing octahedral complexes, where six ligands coordinate to the metal. Other complexes can be described by reference to crystal field theory.
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