Abstract:
Pauling (1931) introduced the concept of the hybridisation of (n - 1)d, ns and np orbitals to explain the two classes 'ionic' and 'covalent' into which co-ordination compounds of transition metals appeared to fall. These two classes in general have different numbers of unpaired spins, hence they will be distinguished by their magnetic moments. For a series of ferric salts a moment corresponding to either one or five unpaired spins was found, but not intermediate values. I the 'ionic' case the five d-electrons go into the 3d orbitals with their spins parallel giving a moment corresponding to five unpaired spins. I the octahedral case d2 sp3 hybridisation occurs, leaving three d-orbitals to hours the five d-electrons thus giving rise to a moment corresponding to one unpaired spin.
