# In the polyatomic ion, CrO4 -2, what is the charge on the chromium atom?

The oxidation state of $C r$ in chromate ion, $C r {O}_{4}^{2 -}$, is $V {I}^{+}$.
As far as anyone knows, the charge in chromate is localized on the oxygen (i.e ${\left(O =\right)}_{2} C r {\left(- {O}^{-}\right)}_{2}$). Chromic acid, ${H}_{2} C r {O}_{4}$ (or ${\left(O =\right)}_{2} C r {\left(- O H\right)}_{2}$), is the precursor; this is a potent oxidant. In each case, the metal oxidation state ($V {I}^{+}$) is clear. Note that in this formal representation, the charge on chromium is neutral. The negative charge is borne by the 2 singly bound oxygen atoms.