Question

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

Answer 1

The oxidation state of `Cr` in chromate ion, `CrO_4^(2-)`, is `VI^+`.

Explanation:

As far as anyone knows, the charge in chromate is localized on the oxygen (i.e `(O=)_2Cr(-O^-)_2`). Chromic acid, `H_2CrO_4` (or `(O=)_2Cr(-OH)_2`), is the precursor; this is a potent oxidant. In each case, the metal oxidation state (`VI^+`) 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.