presence of a lone pair distorts the geomatry of covalent molecule. explain.
Yes! The presence of a lone pair distorts the geometry which can be explained on the basis of VSEPR theory.
Actually, according to the theory the shape of a given species (molecule or ion) depends on the number and nature of electron pairs surrounding the central atom/ion of the species.
The shape or geometry of any molecule depends on the bond angle between the participating atoms and it has been shown that, due to presence of lone pairs of electrons, the bond pairs and the lone pairs itself get repulsion which makes some changes or distortion in the bond angles and hence the geometry is also distorted. It has been seen that, lone pair - lone pair repulsion is greater than lone pair - bonding pair repulsion, which in turn is greater than the bonding pair- bonding pair repulsion.
i.e, (l.p - l.p) repulsion > (b.p - l.p) repulsion > (b.p - b.p) repulsion
Hence, we clearly see that, presence of lone pairs highly causes the repulsion and affects the bond angle and geometry.
For ex:
In Methane, CH4 there is no lone pair, so its hybridization is sp3 and structure and shape both are tetrahedral.
But, in ammonia NH3 the N -atom has a lone pair, so its hybridization is sp3 and structure is tetrahedral but shape becomes like a pyramid and called as pyramidal. as:
