# How many atoms of nitrogen (N) are found in (NH_4)_2CO_3?

Jan 14, 2016

$2$

#### Explanation:

You're dealing with ammonium carbonate, ("NH"_4)_2"CO"_3, an ionic compound made up of ammonium cations, ${\text{NH}}_{4}^{+}$, and carbonate anions, ${\text{CO}}_{3}^{2 -}$.

Now, it's important to realize that in order for ammonium carbonate to be neutral, you need the overall positive charge of the cation to balance the overall negative charge of the anion.

This is what that $2$ subscript denotes - the $1 +$ charge of the ammonium cation tells you that you need two such cations in order to balance out the $2 -$ charge of the carbonate anion.

Since one ammonium cation contains

• one nitrogen atom, $1 \times \text{N}$
• four hydrogen atoms, $4 \times \text{H}$

it follows that two ammonium cations will contain

• two nitrogen atoms
• eight hydrogen atoms

Therefore, one formula unit of ammonium carbonate will contain two atoms of nitrogen, one from each ammonium cation.