CBSE Class 12 · 2003 · Foreign · Coordination CompoundsShort Answer

Using the valence bond approach, predict the shape and magnetic behaviour of [CoCl

_{4}

]

^{2 -}

. (Atomic number of Co = 27)

Answer: Tetrahedral (sp³); paramagnetic with 3 unpaired electrons.

Solution

Co oxidation state: x + 4(−1) = −2 ⇒ Co

^{2 +}

= 3d

^{7}

.
Cl

^{-}

is a weak-field ligand — no pairing; the ligands use the 4s and three 4p orbitals: sp

^{3}

hybridisation.
Shape: tetrahedral.
Magnetism: 3d

^{7}

has 3 unpaired electrons → paramagnetic (μ = √15 ≈ 3.87 BM).

CBSE Class 12 Board · 2003 · Foreign · Subjective