Question

How does Sp3 hybridization work for Nitrogen in `NH_2^-` ?

Answer 1

There are formally 4 electron pairs distributed around the nitrogen in the amide molecule; `sp^3` hybridization would be the description.

Explanation:

Of course, there are likewise 4 electron pairs distributed around the nitrogen centre in ammonia, `:NH_3`. `sp^3` hybridization would be the description, and the gross structure (of electron pairs) is that of a tetrahedron. But we describe molecular geometry on the basis of actual atoms, so the structure of ammonia is pyramidal.

Likewise for `H_2N^-`, the amide ion, the 4 electron pairs are distributed around nitrogen as a tetrahedron. Again, we describe structure on the basis of `N-H` bonds only. The structure of the amide ion is thus akin to that of water, that is bent because there are also 2 lone pairs on the central oxygen/nitrogen atom.

Answer 2

Sp3 hybridization for Nitrogen in `NH_2^-` has tetrahedrical geometry

Explanation:

Nitrogen has 5 outer electrons, in `NH_2^-` it gains an extra electron. Of the 6 electrons, 2 are shared with 2 hydrogen atoms to form 2 sigma bonds, the remaining 4 eletrons fill 2 orbitals with 2 lonely electron pairs, similarly to `H_2O`.