有一个理论。叫做价电子互斥理论。
VSEPR theory
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Valence shell electron pair repulsion (VSEPR) theory (1957) is a model in chemistry, which is used for predicting the shapes of individual molecules, based upon their extent of electron-pair electrostatic repulsion, determined using steric numbers.[1] The theory is also called the Gillespie-Nyholm theory after the two main developers, and VSEPR is sometimes pronounced as "vesper" which is easier to say.
The premise of VSEPR is that to predict the geometric shape and lone-pair behavior of a molecule one must consider : the constructed Lewis structure, expanded to show all lone pairs of electrons, alongside protruding and projecting bonds, as well as consider the total steric number of that molecule.
VSEPR theory is based on the idea that the geometry of a molecule or polyatomic ion is determined primarily by repulsion among the pairs of electrons associated with a central atom.The pairs of electrons may be bonding or nonbonding (also called lone pairs).Only valence electrons of the central atom influence the molecular shape in a meaningful way.
Basic assumptions
Pairs of electrons in the valence shell of a central atom repel each other.
These pairs of electrons tend to occupy positions in space that minimize repulsions and maximize the distance of separation between them.
The valence shell is taken as a sphere with electron pairs localizing on the spherical surface at maximum distance from one another.
A multiple bond is treated as if it is a single electron pair and the two or three electron pairs of a multiple bond are treated as a single super pair.
Where two or more resonance structures can depict a molecule the VSEPR model is applicable to any such structure.
Three types of repulsion take place between the electrons of a molecule:
The lone pair-lone pair repulsion
The lone pair-bonding pair repulsion
The bonding pair-bonding pair repulsion.
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