Provide the structures of the following ions:
$1.$ $CrO_4^{2-}$
$2.$ $Cr_2O_7^{2-}$

(N/A) $1.$ The chromate ion $(CrO_4^{2-})$ has a tetrahedral structure where the central $Cr$ atom is bonded to four oxygen atoms. The bond angles are approximately $109.5^{\circ}$.
$2.$ The dichromate ion $(Cr_2O_7^{2-})$ consists of two $CrO_4$ tetrahedra sharing a common oxygen atom at one corner. The $Cr-O-Cr$ bond angle is approximately $126^{\circ}$.