“Peter Irks Rhea and Commits Felony” is an easy way to remember the Spectrochemical series. Reply

1. Peter Irks Rhea. Commits Critical Felony. Felony committed at Night is Minimum.

2. Cold Condition. (say) NO 2 Night Halting (for 3 Hrs). Non-Committed-Souls Head 2 Office. Office Hours For Super-Committed-Nerds Closes Before.

In a crystal field the d-orbitals of the metal ions gain degeneracy due to Ligand electrons. (That is the equal energy levels of d-orbitals of metal are now unequal due to electron repulsion from Ligand, depending on in which direction the d-orbitals are pointed to Ligand)

Which ions (or Ligands) are more powerfully degenerated (or degenerative) and which are less? There is an order called Spectro-Chemical series.

So I just thought a little to easily remember the series.

1. When geometry (eg tetrahedral or octahedral) and Ligands are fixed how does it affect the metal ions? More splitting denoted by >.

(strong field) Pt4+ > Ir3+ > Rh3+ > Co3+ > Cr3+ > Fe3+ > Fe2+ > Co2+ > Ni2+ > Mn2+ (weak field)

2. When geometry and metal ions are fixed how are Ligands affecting?

CO (~) CN- > NO2- > NH3 > NCS- > H2O > OH- > F- > SCN- (~) Cl- > Br-


The concept behind Crystal Field Theory (Incidentally developed by Physicists like Hans Bethe as an alternative to Valence Bond theory) is described in detail here.

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