d-block fundamentals, CFT, magnetism, colour

What does Crystal Field Theory actually assume?

CFT assumes the ligand-metal interaction is purely electrostatic, using unhybridised metal d orbitals to describe the electron arrangement. The notes say it is useful for magnetic behaviour, colour, structure, and thermodynamic properties, but it does not explain bonding itself.

What happens to the d orbitals in an octahedral field?

The five d orbitals split into eg and t2g sets, separated by Δo. The lecture notes show eg raised by 3/5Δo and t2g lowered by 2/5Δo​, with the total d-orbital energy unchanged overall.

Which octahedral d counts can be either high spin or low spin?

Only d4 through d7 can be either high spin or low spin in octahedral complexes. That is the key range to watch for when the question asks you to compare weak-field and strong-field ligands.

What is the tetrahedral splitting rule?

For the same metal-ligand distances,

Δt=4/9Δo

. The notes also stress that tetrahedral splitting is relatively small, so low-spin tetrahedral complexes are rare.

What does the spectrochemical series tell me?

It orders ligands from weak field, small splitting to strong field, large splitting. The lecture slide places ligands such as I− and Br− at the weak-field end and CN− and CO at the strong-field end.

How do I use the magnetic moment equation?

Use μeff= square root n(n+2)​, where n is the number of unpaired electrons. The lecture examples give 2 unpaired electrons as 2.8 BM and 4 unpaired electrons as 4.9 BM.

What should I look for before using the magnetic moment equation?

Count unpaired electrons from the d-electron configuration, then use the spin-only formula. The heavier d-block notes add that experimental values can deviate because spin-orbit coupling alters the simple spin-only picture.

What are the selection rules for d-d transitions?

the key rules are ΔS=0 and the Laporte rule, Δl=±1. In centrosymmetric octahedral complexes, d-d transitions are formally forbidden, while tetrahedral complexes relax the Laporte rule and are generally much more intense.

Why are d-d bands still observed in octahedral complexes?

The notes give two main relaxation mechanisms, vibronic coupling and p-d mixing through π-donor or π-acceptor ligands. That is why octahedral d-d bands are weak rather than absent.

How do I use the energy equation for colour questions?

The lecture slide shows the transition energy as E=hν, so use it when a question links absorption to an electronic transition. In exam wording, look for the absorbed wavelength or wavenumber, then connect higher Δ

with higher-energy light.

What is the exam link between ligand field strength and colour?

Stronger-field ligands give larger d-orbital splitting, so they absorb higher-energy light. The colour notes explicitly tie the spectrochemical series to absorbance energy and complex colour.

What geometry does the folder say is favoured for Ni, Pt, and Pd complexes?

The notes say NiCl4^2− is tetrahedral, while PtCl4^2− is square planar, and Pt and Pd complexes generally favour square planar arrangements because their larger, more diffuse d orbitals and larger splitting make that geometry preferable.