CBSE Class 12-science Answered

Ligands that produce a small Δ are called weak-field ligands and lie at the left end of the series. Ligands that produce a large Δ are called strong-field ligands and lie at the right end of the series. For example in case of octahedral complexes, the weak-field ligands give rise to small Δ_o and thus are high spin while strong-field ligands give rise to large Δ_o and are low spin.

Water always gives rise to small splittings of the enregy of the d-orbitals for first row transition metal ions and hence is referred to as a weak field ligand. Conversely, CN^- is a strong field ligand, since it causes large splittings of the energy of the d-orbitals.