# What is the formal charge of N in NH_4^+?

Apr 26, 2016

The formal charge of $N$ is $+ 1$, i.e. it is the charge of the ion.

#### Explanation:

Consider the ammonia molecule, ${H}_{3} N :$, which is formally neutral Why so? Because it has 2 inner shell electrons, it has a half share of the 6 electrons that comprise the $3 \times N - H$ bonds, and it gets the full contribution from the lone pair of electrons: $2 + 3 + 2 = 7 {e}^{-}$. This electronic charge balances the 7 positively charged protons present in the nitrogen nucleus. In ammonium, it still gets the 2 inner core electrons, but only half of the $4 \times N - H$ electrons, i.e. 6 electrons in total, and thus a formal positive charge.

This can also be seen in the acid-base reaction:

$N {H}_{3} \left(a q\right) + {H}_{2} O r i g h t \le f t h a r p \infty n s N {H}_{4}^{+} + H {O}^{-}$.

Charge is conserved as always.

In liquid ammonia, the amide ion, $N {H}_{2}^{-}$, is known, as well as the imide ion, $N {H}^{2 -}$. By means of the formalisms above, can you tell me where the formal charge lies?