Transition Metal Ions and their Complexes Ligand Field Theory

The transition metal ions contain an incomplete d shell of electrons and the correlation between the presence of an incomplete d shell and the display of colours by the transition metal ions can be clearly seen from Table 12.L It is to be noted that ions with no d electron or with the maximum number of d electrons are colourless, while those with half-filled d shells exhibit only a very pale colour. 

Total No. of d electrons I j Number of unpaired d electrons j Metal ion 1 Colour i  

5 5 l Mn2+ Fe + Very pale pink Very pale violet  

The colours of the transition metal ions and their complexes are, in fadt, due to electronic transitions involving the d electrons. The d shell in an atom or ion is five-fold degenerate, i.e. there are five d orbitals which are equal in energy in the absence of an external magnetic or electric field. An electron 

of d electrons electrons stabili- electrons j electrons stabili- 

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