Crystal Field Model: True/False Questions for Octahedral Complex Ions

[SamTsui86]

Homework Statement

Which of the following are true for the Crystal Field Model of an octahedral complex ion? Consider ions to be from first-row transition metals.



a) Two of the 3d orbitals point directly at ligands

b) t2 orbitals are less stable than e orbitals

c) A large crystal field splitting energy results in a diamagnetic complex

d) The high-spin case gives maximum unpaired electrons

e) For a given ligand, Fe3+ increases splitting less than Fe2+

f) Cl- causes a greater increase in the crystal field splitting energy than does H2O

g) The splitting of energy (E) of 3d orbitals occurs in the ligands

Homework Equations

The Attempt at a Solution

I put acde and I am pretty sure I am right, what am I doing wrong?

 

[NotMrX]

Homework Statement

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c) A large crystal field splitting energy results in a diamagnetic complex

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g) The splitting of energy (E) of 3d orbitals occurs in the ligands

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The statement c isn't technically right and g is unclearly worded to me.

For statement C if there are an odd number of electrons it is still diamagnetic. By most standards diamagnetic means no unpaired electrons and if there are an odd number electrons it going to have to be unpaired. A large splitting energy makes it hard to move the electons up in energy to the Eg orbitals but the unpaired electron can occur in T2g orbitals

Statement G: Crystal field theory assumes coulombic repulsion. The ligands attach on the axis making a higher electron density on those 2 d orbitals. This increases the repulsion and that is why those two orbitals split and become higher in energy. So in a way the splitting energy does come the ligands

 

[Blueshift5]

Your response is mostly correct, but there are a few errors.

a) True - Two of the 3d orbitals (dx^2-y^2 and dz^2) point directly at ligands in an octahedral geometry.

b) False - t2 orbitals are actually more stable than e orbitals due to their lower energy.

c) True - A large crystal field splitting energy results in a diamagnetic complex, meaning there are no unpaired electrons.

d) False - The low-spin case actually gives maximum unpaired electrons.

e) False - For a given ligand, Fe3+ actually increases splitting more than Fe2+.

f) True - Cl- causes a greater increase in the crystal field splitting energy than H2O due to its smaller size and higher charge.

g) False - The splitting of energy (E) of 3d orbitals occurs in the presence of the ligands, not within them.