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?

1 Answer
Jul 7, 2016

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

Explanation:

There are 4 electron pairs around the nitrogen atom: 3×NH bonds, and one nitrogen-centred lone pair. The lone pair is stereochemically active (and hence NH3 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.

NH3(aq)+H2O(l)NH+4+HO

Given 2 inner core electrons, and a half share of the 8 electrons that compose the 4×NH 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.