Question

Why does $N{H_3}$ act as a Lewis base?

Answer 1

Hint : A Lewis base is a substance that can donate a pair of non bonding electrons. A Lewis base is therefore called electron-pair-donor. In Lewis base molecules the orbitals used to be highly occupied so they have a tendency to donate electrons. The most common Lewis base is ammonia .

Complete answer:

In ammonia the molecule consists of a nitrogen atom as a central metal atom. Ammonia is Lewis base because nitrogen has a lone pair of electrons which can be donated, hence it acts as Lewis base. $N{H_3}$ can give a lone pair of electrons to protons to form ammonium ions . This reaction shows its Lewis base tendency. $N{H_3} + {H^ + } \to N{H^ + }_4$ $\Rightarrow$ Here in this reaction the lone pair on the nitrogen atom is transferred to the hydrogen ion . Hydronium ion acts as a Lewis acid here which accepts electrons from ammonia.
A Lewis acid-base reaction can be done when a Lewis base donates a pair of electrons to an Lewis acid. Lets see an example of Lewis acid-base reaction. In the following reaction each of two ammonia molecules which is a Lewis base donates a pair of electrons to a silver ion which acts as Lewis acid in the reaction.
There are so many reactions that are Lewis acid-base displacement reactions.
Note : Here we learned about Lewis base and also learned why ammonia acts as a Lewis base in any reaction. Ammonia has a filled orbital containing an electron pair which does not involve bonding and Lewis acid contains an empty orbital which is capable of accepting electrons.