Valence shell electron pair repulsion (VSEPR) theory is a model in chemistry, which is used to predict the molecular structure as well as their shapes, based on electron pair-electron pair electrostatic repulsion with the help of steric numbers. The basic assumptions of VSEPR theory are-
- Electron pairs in a valence shell repel each other.
- The electron pairs try to minimize this repulsion to the best and accordingly they orient themselves in such a manner in three dimensional spaces.
- The valence shell is considered to be a sphere where the electron pairs are remain oriented on the surface of that sphere maintaining the highest possible repulsion.
- A multiple bond is generally treated as a single electron pair and the two or three electron pairs of a multiple bond are treated as a single electron pair.
- For two or more canonical structures of a molecule, the VSEPR model is equally applicable to any such structure. Three types of repulsive interaction take place between the electrons of a molecule:
- Lone pair-lone pair repulsion
- Lone pair-bonding pair repulsion
- Bonding pair-bonding pair repulsion.
A molecule must avoid these repulsions to remain stable. When repulsion cannot be avoided, the weaker repulsion (i.e. the one that causes the smallest deviation from the ideal shape) is preferred.
The lone pair-lone pair (lp-lp) repulsion is considered to be stronger than the lone pair-bonding pair (lp-bp) repulsion, which in turn is stronger than the bonding pair-bonding pair (bp-bp) repulsion. Hence, the weaker bp-bp repulsion is preferred over the lp-lp or lp-bp repulsion.
- Two electron pairs in the valence orbital are arranged linearly and the central atom is sp
- Three electron pairs are organized in a trigonal planar arrangement and the central atom is sp2
- Four electron pairs are organized in a tetrahedral arrangement and the central atom is sp3
- Five electron pairs are arranged in a trigonal bipyramid structure and the central atom is sp3d
- Six electron pairs are organized in an octahedral arrangement and the central atom is sp3d2
- Seven electron pairs are organized in an octahedral arrangement and the central atom is sp3d3
Here is a GAMSAT type question from this topic. Check it and try to solve it yourself.
What is the hybridization of the central atom in AX5 type molecule (A: Pentavalent, B: Univalent)?