Question

What is the oxidation number of Cr In CrO5? Why?

Answer 1

If we want to find out Oxidation no. of Cr in CrO5 by general method it would be +10  which is wrong   as in its real structure one Cr atom is attached  to to 4 oxygen atoms & double-bonded with two O-atoms & single bonded with the rest two O-atoms .Oxygen being more electronegative attracts the shared electron towards itself. The double-bonded O-atoms retains 4 electrons while the single-bonded retains 2  that case one Cr-atom loses 6 electrons & it retains a charge of positive 6+

Answer 2

Answer:

This cannot be true as maximum O. N. of Cr cannot be more than + 6. Since Cr has only five electrons in 3d orbitals and one electron in 4s orbital. This exceptional value is due to the fact that four oxygen atoms in CrO5are in peroxide linkage. The chemical structure of CrO5 is.

Therefore, the evaluation of o.n. of Cr should be made as follows

x + 1 × (– 2) + 4 (–1) = 0

(for Cr) (for O) (for O–O)

or x – 2 – 4 = 0 or x = + 6.