Question

Why does ammonia molecule shows hybridisation although it does not have vacant d orbitals and have 3 p orbitals?

Answer 1

Structure of NH3 can be explained by sp³ hybridization.

Electronic configuration of nitrogen atom : 1s² 2s² 2p³

One 2s orbital and three 2p orbitals hybridize to form four sp³ hybrid orbitals. One sp³ hybrid orbital houses the lone pair and the other three hybrid orbitals bond with hydrogen atoms.

These reasons that can more justify the hybridization of ammonia molecule.

1. Bond angle: If the molecule did not have hybrid orbits, and instead had unhybridized p-orbitals taking part in the bond formation, then the bond angle between the orbitals would be 90 degrees. And as for the real situation, the bond angle is nearly 107 which makes the molecule more stable, decreasing the bond pair-bond pair and bond pair-lone pair repulsion.

2. Energy: Recalling the definition of hybridization, it is the mixing of the atomic orbitals having slightly different energies to form new orbitals that have equal energies. This stabilizes the molecule. As for ammonia molecule due to hybridization, the energies of the lone pair of electrons and the bond pair of electrons becomes almost equal, thereby increasing the stability of the molecule.

3. Geometry: Thinking about the spatial arrangement of the atoms in the molecule of ammonia if there is no hybridization in the molecule then the size of the orbital containing a lone pair of electrons would be different from that of the orbitals containing a bond pair of electrons. Also if hybridization would not be taking place, explaining the geometry of the molecule, that is its trigonal pyramidal shape, would not be possible.