Question
Atomic number of $$Cr$$ and $$Fe$$ are respectively 24 and 26, which of the following is paramagnetic with the spin of electron ?
A.
$$\left[ {Cr{{\left( {CO} \right)}_6}} \right]$$
B.
$$\left[ {Fe{{\left( {CO} \right)}_5}} \right]$$
C.
$${\left[ {Fe{{\left( {CN} \right)}_6}} \right]^{4 - }}$$
D.
$${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }}$$
Answer :
$${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }}$$
Solution :
Atoms, ions or molecules having unpaired electrons are paramagnetic. In $${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }},Cr$$ is present as $$Cr\left( {{\text{III}}} \right).$$
$$C{r^{3 + }} = 1{s^2},2{s^2}2{p^6},3{s^2}3{p^6}3{d^3}$$
In excited state
Number of unpaired electrons =3, so it is paramagnetic while rest of the species are diamagnetic.
Atoms, ions or molecules having unpaired electrons are paramagnetic. In $${\left[ {Cr{{\left( {N{H_3}} \right)}_6}} \right]^{3 + }},Cr$$ is present as $$Cr\left( {{\text{III}}} \right).$$
$$C{r^{3 + }} = 1{s^2},2{s^2}2{p^6},3{s^2}3{p^6}3{d^3}$$
In excited state
Number of unpaired electrons =3, so it is paramagnetic while rest of the species are diamagnetic.