Ammonia is , a pyramidal molecule with a nitrogen lone pair. The lone pair can accept a proton to form ammonium or coordinate a Lewis acid.
In water, the Ammonia-ammonium equilibrium affects pH. Molecular Ammonia and the ammonium ion therefore have different charge states and should not be treated as interchangeable species.[ref]
https://webbook.nist.gov/cgi/cbook.cgi?ID=C7664417&Units=SI. NIST Chemistry WebBook: ammonia, formula and molecular identity
[ref]
Chemistry 2e by Paul Flowers and others. Chapter14, Acid-Base Equilibria: ammonia-ammonium equilibrium and weak bases
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