Ligand Field Theory and Pi Bonding in Complexes · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

From dots to orbitals in metal complexes

Science · Chemistry · ages 20-21
Name ______________________   Date ____________

  1. In ligand field theory, each ligand group orbital mixes only with a metal orbital of the same symmetry label.

    Circle one:   True   False

  2. What does crystal field theory get right, and where does it fail?

    • It gets the two up three down pattern right but cannot explain pi effects
    • It explains pi bonding but gets the pattern wrong
    • It explains everything about every complex

  3. How does a pi donor ligand such as fluoride move the splitting gap?

    • It pushes the lower set up and narrows the gap
    • It pulls the lower set down and widens the gap
    • It leaves every level exactly where it was

  4. Cyanide gives a much larger splitting than fluoride. What is the orbital reason?

    • Fluoride is smaller, so it must always split more
    • Both ligands are pure sigma donors with no pi role
    • Cyanide accepts pi density while fluoride donates it, so their gaps move opposite ways

  5. Why does carbon monoxide sit at the strong end of the series although it is neutral?

    • Its large size crushes the metal orbitals together
    • It accepts metal density back into empty pi orbitals, which widens the gap
    • It refuses all sigma bonding and binds purely by charge

  6. How do you build the octahedral orbital diagram in ligand field theory?

    • Build ligand group orbitals, mix them with matching metal orbitals, and read the gap between the resulting levels
    • Place dots around the metal and read off their charges
    • Count the ligands and multiply by the metal charge

  7. Replacing water ligands with cyanide widens the gap of a complex. Which level moves and how?

    • The upper set drops while the lower set stays fixed
    • Both sets rise together by the same amount
    • The lower set is pulled down by back donation, so the space above it grows

  8. A student explains the series order using ligand charges alone. What breaks in that argument?

    • Nothing breaks, since charge predicts the whole series
    • Neutral ligands such as CO would rank low, yet CO tops the series through back donation
    • Charged ligands would all rank identically, which they do
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Answer key

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

From dots to orbitals in metal complexes W1-mt_Gq3JG7F7Nl-s1

  1. True · That symmetry matching is the machine that rebuilds the gap from overlap.
  2. It gets the two up three down pattern right but cannot explain pi effects · Point charges reproduce the shape of the split while saying nothing about donation or acceptance.
  3. It pushes the lower set up and narrows the gap · Filled ligand pi orbitals shove extra density at the metal lower set from above.
  4. Cyanide accepts pi density while fluoride donates it, so their gaps move opposite ways · Acceptance stretches the gap while donation compresses it, which orders the pair.
  5. It accepts metal density back into empty pi orbitals, which widens the gap · The return gift of back donation stabilises the lower set and stretches the gap wide.
  6. Build ligand group orbitals, mix them with matching metal orbitals, and read the gap between the resulting levels · Mixing by symmetry splits the levels, and pi effects then shift the rungs.
  7. The lower set is pulled down by back donation, so the space above it grows · Swapping a donor for an acceptor flips the pi shift from pushing up to pulling down.
  8. Neutral ligands such as CO would rank low, yet CO tops the series through back donation · Charge language cannot see pi acceptance, so it misplaces the neutral acceptor CO.
Worksheet · LightMySky