High spin or low spin

Science · Chemistry · ages 19-21

Name ______________________ Date ____________

Which pair sits at the strong field end of the series?
- Fluoride and water
- Cyanide and carbon monoxide
- Chloride and bromide
How do you decide between high spin and low spin?
- Compare the splitting energy with the pairing energy
- Count the ligands
- Measure the temperature
Ligand field strength follows directly from ligand charge.
Circle one: True False
The same d5 ion is forced low spin by cyanide. Type its number of unpaired electrons.
Answer: ______________
An octahedral d5 ion is high spin. Type its number of unpaired electrons.
Answer: ______________
A complex has a spin-only moment near 4.90 Bohr magnetons. How many unpaired electrons does it hold?
- Three
- Five
- Four
A tetrahedral cobalt complex is probably low spin.
Circle one: True False
An octahedral iron complex shows one unpaired electron. What do you conclude?
- High spin with a weak field ligand
- Low spin with a strong field ligand
- Tetrahedral with a weak field ligand

Answer key

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

Cyanide and carbon monoxide · Cyanide and carbon monoxide cause big splits and low spin.
Compare the splitting energy with the pairing energy · The cheaper option, spreading out or pairing up, wins.
False · Neutral carbon monoxide outranks fluoride despite having no charge.
1 · Low spin d5 pairs four electrons and leaves one single.
5 · High spin d5 spreads one electron per level with none paired.
Four · Four unpaired electrons give about 4.90 Bohr magnetons.
False · The tetrahedral gap is tiny, so pairing never pays.
Low spin with a strong field ligand · One unpaired d5 means low spin, which needs a strong field ligand.