Transition and Inner Transition Elements — Chemistry STD 12 Science — Question
Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryTransition and Inner Transition Elements3 Marks
Question
Explain different oxidation states of chromium.
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Answer
The observed electronic configuration of chromium is, ${ }_{24} \operatorname {Cr}[ Ar ] 3 d ^5 4 s ^1$..
Different possible oxidation states of $Cr$ are $4-1 \left(3 d^5\right),+2\left(3 d^4\right),+3\left(3 d^3\right),+4\left(3 d^2\right)$ + $5\left(3 d^1\right)$ and $+6\left(3 d^{\circ}\right)$.
Although in $+1$ state, $Cr$ gets extra stability of half$-$filled $3 d^5 \ -$orbital, it does not exhibit $+1$ state in common except with pyridine.
$Cr^{+2}$ has few stable salts like $CrCl_2, CrSO_4$ while $Cr^{+3}$ forms very stable salts like $CrCl_3.$
$Cr^{+4}$ and $Cr ^{+ 5}$ are unstable oxidation states.
$Cr^{+6}$ is the most stable state due to inert gas $[Ar]$ electronic configuration and form the salts like $K_2Cr_2O_7.$
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