How is NH_3 acting in the reaction H^++:NH_3 ->[H:NH_3]^+according to the Lewis definition?

1 Answer
Jan 4, 2015

NH_3 is acting as an electron donor, so by definition it is a Lewis base.

The lone pair of elctrons from the N-atom is (mainly) donated to, are shared with, the proton (H^+), after which all four H's fill up a nice tetrahedron around the N.

The representation of [H:NH_3]^+ is not really correct, as all H-atoms are completely equal, and the electron deficit (the overall +) is shared around the whole [NH_4]^+ ammonium -ion.

If the ammonium-ion is dissociated (e.g. in hot alkalic surroundings), there is no telling which of the four H's will leave.