ammonium ion vs ammonia

ammonium ion and ammonia both are nouns.

Word	Noun	Adjective	Verb	Adverb
ammonium ion	Yes	No	No	No
ammonia	Yes	No	No	No

As nouns, ammonia is a hypernym of ammonium ion; that is, ammonia is a word with a broader meaning than ammonium ion:

ammonium ion: the ion NH4 derived from ammonia; behaves in many respects like an alkali metal ion
ammonia: a pungent gas compounded of nitrogen and hydrogen (NH3)

ammonium ion (noun)	ammonia (noun)
the ion NH4 derived from ammonia; behaves in many respects like an alkali metal ion	a pungent gas compounded of nitrogen and hydrogen (NH3)
	a water solution of ammonia