Question

In $C{r_2}O_7^{2 - }$ every Cr is linked to:
A.two O atoms
B.three O atoms
C.four O atoms
D.five 0 atoms

Answer 1

Hint: Dichromate salts contain $C{r_2}O_7^{2 - }$ dichromate anion. These are oxoanions of chromium with +6 oxidation state and they are good oxidizing agents as they are linked to oxygen atoms. Two chromium atoms are bonded with a single oxygen atom between them and the rest of the oxygens are bonded to individual chromium atoms in equal ratio.

Complete step by step answer:
Dichromate ion is a divalent inorganic anion .It is a chromium oxoanion and has a molecular formula $C{r_2}O_7^{2 - }$ . It is a conjugate base of hydrogen dichromate. Dichromate ion is obtained by removing both protons from dichromic acid $({H_2}C{r_2}{O_7})$ . It is used as an oxidizing agent. Due to its ionic property it forms many salts which can be used in many oxidation-reduction reactions.
The charge on the dichromate ion is -2 and the oxidation state of chromium in $C{r_2}O_7^{2 - }$ is +6. The $C{r^{6 + }}$ ion has 4s and 3d vacant orbitals . These orbitals combine to give $s{d^3}$ hybrid orbitals. Thus, each $C{r^{6 + }}$ ion in the dichromate $(C{r_2}O_7^{2 - })$ ion is $s{d^3}$ hybridised. Due to this dichromate ion consists of two tetrahedrons sharing an oxygen atom at the common vertex. Therefore, each of the two chromium atoms at the centre of the tetrahedra bond to four oxygen atoms.
 

Hence, option (C) is the correct answer

Note: There are six \[Cr - O\] terminal bonds in dichromate ions. These bonds are equivalent due to resonance. The two \[Cr - O\] bonds which share an oxygen atom are longer than the other six equivalent \[Cr - O\] bonds. This defines the structure of dichromate anion along with bond angles.