CBSE Class 12 · 2003 · Foreign · Coordination CompoundsShort Answer

Using the valence bond approach, deduce the shape and magnetic behaviour of the [Cr(NH

_{3}

)

_{6}

]

^{3 +}

ion. [Atomic number of Cr = 24]

Answer: Octahedral (d²sp³), paramagnetic — 3 unpaired electrons (μ = √15 ≈ 3.87 BM).

Solution

^{3 +}

= [Ar]3d

^{3}

: three unpaired electrons in three 3d orbitals.
Two vacant 3d + 4s + three 4p orbitals hybridise as d

^{2}

^{3}

, accepting six NH

_{3}

lone pairs.
Shape: octahedral (inner-orbital complex).
Magnetism: 3 unpaired electrons → paramagnetic, μ = √15 ≈ 3.87 BM.

CBSE Class 12 Board · 2003 · Foreign · Subjective