Q6(b). Pale colours and line-like spectra of lanthanide ions
Why are 4f metal ions (lanthanide ions) generally pale in colour? Why do they show line-like electronic spectra?
Answer in brief
The colour comes from 4f–4f transitions, which are Laporte forbidden; the 4f shell is buried under the filled 5s²5p⁶ shell, so the bands stay very weak (pale) and are not broadened by ligands (sharp lines).
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Coverslanthanide colourf–f transitionsLaporte ruleshielding of 4f orbitalsline-like spectralanthanide spectra
All parts of Question 6
- 6(a) Metal–metal bonds in Cp₂Fe₂(CO)₄; structure of Bi₅³⁺10 marks
- 6(b) Pale colours and line-like spectra of lanthanide ions10 marks
- 6(c) Neutral mixed sandwich compound of a d⁶ centre10 marks
- 6(d) Separating XeF₆; diborane with NH₃ and with Me₃N10 marks
- 6(e) Origin of the yellow colour of aqueous FeCl₃10 marks