Why do #Cu^+# , #Fe^(3+)# and #Mn^(2+)# have colored solutions despite having half filled and full filled d orbitals?
1 Answer
Mn²⁺ and Fe³⁺ have coloured solutions because the water ligands split the d orbitals into different energy levels.
Transition metal ions in solution exist as hydrates, e.g., Cu(H₂O)₆⁺, Mn(H₂O)₆²⁺, and Fe(H₂O)₆³⁺.
The ligands split the d orbitals into two groups — two with a higher energy than the other three.
The colours are caused by electronic transitions from the lower level to the higher level (d → d transitions).
Cu⁺ Colour
The electron configuration of Cu⁺ is [Ar] 3d¹⁰.
All five orbitals are completely filled. No d → d transitions are available, so solutions of Cu⁺ ions are colourless.
Mn²⁺ and Fe³⁺ Colours
The electron configurations of Mn²⁺ and Fe³⁺ are [Ar] 3d⁵.
Those five electrons are in the lower level.
You can have d → d transitions to the higher level, so solutions of these ions are coloured.
Here is a table of the colours of various transition metal ions.
