Answer: The lone pair of electrons on the nitrogen in ammonia decreases the bond angle between the bonding pairs, giving it a pyramidal structure.
Explanation:
Formula used
[tex]:{\text{Number of electrons}} =\frac{1}{2}[V+N-C+A][/tex]
where, V = number of valence electrons present in central atom
N = number of monovalent atoms bonded to central atom
C = charge of cation
A = charge of anion
1. [tex]NH_3:[/tex]
[tex]{\text{Number of electrons}} =\frac{1}{2}[5+3-0+0]=4[/tex]
The number of electrons is 4 that means the hybridization will be [tex]sp^3[/tex] and the electronic geometry of the molecule will be tetrahedral.
But as there are three atoms around the central carbon, the fourth position will be occupied by lone pair of electrons. The repulsion between lone and bond pair of electrons is more and hence the molecular geometry will be trigonal pyramidal.
2. [tex]BF_3:[/tex]
[tex]{\text{Number of electrons}} =\frac{1}{2}[3+3-0+0]=3[/tex]
The number of electrons is 3 that means the hybridization will be [tex]sp^2[/tex] and the electronic geometry of the molecule will be trigonal planar.
