# What are the brackets for around the Lewis structure?

##### 1 Answer
Jan 29, 2017

They allow one to unambiguously describe the charge of the overall ion. Here is an example:

For ${\text{NH}}_{4}^{+}$, more accurately ${\left[{\text{NH}}_{4}\right]}^{+}$ (as the positive formal charge does not belong to hydrogen), we have a formal charge on $\text{N}$ of $4 - 3 = + 1$, while each $\text{H}$ has a formal charge of $1 - 1 = 0$. So, the overall charge adds up to be $+ 1$.

(If you recall, formal charge assumes evenly-shared valence electrons and is $\text{FC}$ $=$ $\text{Valence - Owned}$.)