Q.What are strong field and weak field ligands ? Give one example of each.

Crystal Field Theory (CFT), from Bethe and Van Vleck, treats the metal-ligand bond as purely IONIC/electrostatic (point charges or dipoles), unlike VBT's covalent picture. As ligands approach along real bond directions, the five degenerate d orbitals split into two energy sets. In an OCTAHEDRAL field, orbitals pointing straight at the ligands (dz², dx²-y², the eg set) rise by 3/5 Δ₀, while orbitals pointing between the ligands (dxy, dyz, dxz, the t2g set) fall by 2/5 Δ₀. In a TETRAHEDRAL field the pattern inverts (t2 rises by 2/5 Δt, e falls by 3/5 Δt) and is weaker overall: Δt = 4/9 Δ₀ for the same metal/ligand. …