# 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?

Jul 7, 2016

There are 4 electron pairs around the nitrogen atom: $3 \times N - H$ bonds, and one nitrogen-centred lone pair. The lone pair is stereochemically active (and hence $N {H}_{3}$ 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.
$N {H}_{3} \left(a q\right) + {H}_{2} O \left(l\right) \rightarrow N {H}_{4}^{+} + H {O}^{-}$
Given 2 inner core electrons, and a half share of the 8 electrons that compose the $4 \times N - H$ 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.