Question

Why is ammonia a Lewis base?

Answer 1

Well what is a `"Lewis base...?"`

Explanation:

Is it not an electron pair `"DONOR..."`?

And of course ammonia CAN behave in this capacity...i.e. consider its Bronsted basicity..

`NH_3(aq) + H_2O(l) rightleftharpoonsNH_4^+ + HO^-`

The equilibrium lies to the left as we face the page. And ammonia is a potent ligand towards transitions metals...

`CoCl_3(aq) + 6NH_3(aq) rarr [Co(NH_3)_6]^(3+)+3Cl^-`

The `"hexamine cobalt(III)"` species is a classic Werner compound.

And thus ammonia fits the description...still pretty smelly tho, and when you open the bottle the neighbours complain if you are a bit careless...