Question

If an atom of nitrogen binds with three hydrogen atoms to form a molecule of ammonia, how many lone pairs of electrons does nitrogen have?

Answer 1

The nitrogen atom in ammonia has a formal lone pair of electrons.

Explanation:

There are 4 electron pairs around the nitrogen atom: `3xxN-H` bonds, and one nitrogen-centred lone pair. The lone pair is stereochemically active (and hence `NH_3` is a trigonal pyramid, but tetrahedral with respect to its ELECTRONIC geometry), and we conceive that the lone pair can bind to `H^+` or `C` to form a quaternary nitrogen centre, i.e. an ammoniium salt.

`NH_3(aq) + H_2O(l) rarr NH_4^+ + HO^-`

Given 2 inner core electrons, and a half share of the 8 electrons that compose the `4xxN-H` bonds, the nitrogen has 6 electrons associated with the atom rather than 7, and thus a representation as a formal cation, i.e. quaternized nitrogen.