Where does the lone pair comes from while drawing the flower stucture of NH3? Why does the one of the two electron does not move in the d-orbital in the exited state of NH3? Can you please explain it with the structures.

Diagrammatic Representation:

 

 

                                                                                  

                                                                                  Ammonia molecule

Orbital Overlap:

• Out of the four sp³ hybrid orbitals, one contains a lone pair of electrons and other three are half filled.
• The three half-filled sp³ hybrid orbitals of N atom overlap axially with half-filled 1s orbitals of three hydrogen atoms to form three N- h (sp³-s) sigma covalent bonds.
• In NH₃ molecule, there are three bonding pairs of electrons and one lone pair (non-bonding pair) of electrons.
• The forces of repulsion between lone pair and bond pair of electrons decrease in the following order:
• Lone pair-Bond pair > Bond pair- Bond pair
• Due to this, bonding pair of electrons are pushed together and hence H-N-H bond angle is reduced from 109⁰28’ to 107⁰18’.

       Nitrogen does not have vacant d-orbitals.