Electronic Spectra of Complexes and Tanabe-Sugano Diagrams · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Reading the colours of metal complexes

Science · Chemistry · ages 20-22
Name ______________________   Date ____________

  1. Which jumps appear as the main bands, and which hide?

    • Forbidden jumps appear and allowed ones hide
    • Every possible jump appears with equal height
    • Spin allowed jumps appear as the main weak bands, while spin forbidden ones hide or vanish

  2. A complex shows three absorption bands but has one splitting energy. What does each band connect?

    • Two whole ion states of the full d shell
    • Two single orbitals and nothing else
    • Two different molecules in the sample

  3. A towering intense band beside tiny ones is the giveaway of a charge transfer transition.

    Circle one:   True   False

  4. Why is manganate(VII) deep purple although the metal has no d electrons?

    • Its colour is an allowed ligand to metal charge transfer, which needs no d electrons
    • It still performs d to d jumps using empty orbitals
    • The colour comes from spin forbidden jumps hiding in the spectrum

  5. How do you read a Tanabe Sugano diagram to get the splitting energy?

    • Read the tallest peak position directly as the gap
    • Find the ratio of band positions, match the ratios on the diagram, then read the gap off the axes
    • Count the bands and multiply by the first band position

  6. An octahedral nickel(II) complex shows three weak bands. How are they assigned?

    • As three charge transfer bands from three different ligands
    • As the three spin allowed jumps from the ground state of the d8 ion
    • As one real band plus two instrument artefacts

  7. Two complexes each show one weak band and one towering band. The towering band sits at higher energy in the second complex. What can you conclude?

    • Both towering bands are spin forbidden d to d jumps
    • Both towering bands are allowed charge transfer, and the second leap needs more energy
    • The weak bands are charge transfer and the towering bands are artefacts

  8. A student labels each band of a cobalt complex as a jump between two single orbitals. What is the error?

    • Single orbital jumps would give exactly one band per complex
    • State labels track the symmetry of the whole ion, so bands link many electron states, not single orbitals
    • Orbital labels are forbidden on any diagram
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Reading the colours of metal complexes W1-mt_GQFMqha0es-s1

  1. Spin allowed jumps appear as the main weak bands, while spin forbidden ones hide or vanish · Selection rules thin the crowd, so you read the state ladder through the allowed jumps.
  2. Two whole ion states of the full d shell · Electron repulsion splits each configuration into several states, and each band jumps between two of them.
  3. True · Charge transfer is fully allowed, so its bands tower over the shy d to d peaks.
  4. Its colour is an allowed ligand to metal charge transfer, which needs no d electrons · With zero d electrons no d to d jump exists, so only charge transfer can explain the intensity.
  5. Find the ratio of band positions, match the ratios on the diagram, then read the gap off the axes · The bands fix the parameters, not the reverse: ratios first, then the gap.
  6. As the three spin allowed jumps from the ground state of the d8 ion · Their weakness confirms d to d character, and their spacing gives the gap.
  7. Both towering bands are allowed charge transfer, and the second leap needs more energy · Height names the type as charge transfer, and position names the leap energy.
  8. State labels track the symmetry of the whole ion, so bands link many electron states, not single orbitals · Letters such as A and T describe whole ion states, and crossings and slopes carry the assignments.
Worksheet · LightMySky