Why is the ammonia molecule #sp^3-"hybridized"# even though there are only #3xxN-H# bonds?
Because there are 4 electron pairs around the central nitrogen atom.........
Nitrogen has 5 valence electrons, and it forms
Because there are FOUR electron pairs around the central nitrogen atom, VESPER predicts tetrahedral geometry with respect to the disposition of the electron pairs. But because we describe molecular geometry on the basis of atoms NOT on electron pairs.....the geometry of ammonia descends from tetrahedral to trigonal pyramidal, and this treatment is in actual accord with the OBSERVED geometry.