试论价层轨道的杂化——兼论杂化轨道理论与价层电子对互斥理论的统一

Valence Shell Orbital Hybridization Theory

在分子结构理论中,杂化轨道理论在多原子分子的空间构型被实验确定后,能够根据一定的假设给出合理的解释;价层电子对互斥理论主要用于预测分子或离子的空间构型,但其假设有些生硬、推理不够严密,对VP与电子对空间构型之间关系的推导比较繁琐,不易理解,也不能很好地解释一些多原子分子(如PF5、IF7等分子)中存在键长不等的现象。两种理论在各自的领域都取得了很大的成功,也各有其不足之处,一直未能统一。价层轨道杂化理论正是在综合了这两种理论的优点之后得到的。该理论在假设较少———即假设中心原子的价层轨道在成键时都要发生杂化,该假设与实验事实完全相符———的前提下,利用立体几何学原理对多原子分子的空间构型进行了非常简洁的推导,其结果不仅可全部继承前两种理论的成功之处,而且还能解释多原子分子中出现的键长不同、存在异构体等现象,这是其独到之处,也是其创新之处。

In the modern molecular structure theory, the hybridization theory can be applied to explain the structure of polyatomic molecules after it has been determined by experiment. The VSEPR theory is mainly applied to predict the geometries of molecules and ions and it is surprisingly useful, but its rules appear somewhat arbitary and its deduction to the relation between VP and the geometry of the electron pairs is troublesome and hard to justify in a rigorous quantum - mechanical formulation, and it cannot explain the difference of the bend length in some molecules such as PF5 and IF7, etc. These two theories has gained great achievement in their very field while their shortcomings exist and haven＇ t been combined to a synthetic theory which can be applied anywhere. Valence shell orbital hybridization theory is exactly a synthetic theory that it has absorbed the advantages of these two theories. In this paper, a concise deduction has been given to the relation between VP and its molecular structure by means of stereo - geometry from little assumption, which assumes the valence shell orbitals of the central atom will be hybridized when bonding, which tally with experimental facts very well. It can not only carry on the achievement of the former theoties, but also explain the difference of the bend length and isomerism in some molecules, and that is the originality and innovation of the theory.