This is a short critical thinking exercise that I use to assess whether my students have understood where the d orbital splitting in Octahedral and Tetrahedral geometry comes from. I do it at the beginning of the class after we discuss CFT/LFT in Oh and Td compounds.
The student should be able to
- draw a representation of the three dimensional structure of a coordination complex in a given geometry (in this case trigonal pyramidal)
- Identify the point group of a molecule based on a three dimesional representation of the structure.
- correctly predict/identify the sets of degenerate d orbitals that will exist in a given symmetry
- apply critical thinking to order these sets of degenreate d orbitals in terms of energy based on the electronc repulsion between the d orbital electrons and the ligand field.
- correctly fill in a d orbital splitting MO diagram to determine the ground state, applying Aufbau, Hunds Rules and Pauli exclusion principle, for either high or low spin and for any d electron count provided.
- translate the filled d orbital splitting diagram into an expression of the electron configuration
- use the MO diagram to calculate the spin only value of the magnetic moment.
None required, but student often like to use a model kit. The inorganic organic model kit containing a trigonal bipyramidal central atom could prove useful.
I use this execise as an assessment tool on the lecture day AFTER we cover CFT/LFT for octahedral and tetrahedral complexes in class.
Students get active feedback on their assignment of point group during the exercise.
At the end of the exercise students report out their answrs on the board, or turn in the paper.
I followed up ith a similar exam question for a seesaw shape (to be posted on VIPEr)
In my class of 11 senior chem majors this term (ther first term that I've used this)
- two students incorrectly identified the point group initially, but were able to corrrect once I pointed out the step in the flow chart where they erred. I do not tell students the answer, preferring instead to let them work it out.
- students unanimously selected the dz2 orbital (A1g) as the highest energy, but we had a really nice discussion of the ordering or the two E sets. Without knowing the ligands and Metal, their ordering may not be predicted correctly in any case. This went nicely with the assignment from the previous lecture where I had them read the recent paper by Tobias Ritter et al, explainin this same complication for square planar complexes: http://pubs.acs.org/doi/abs/10.1021/acs.jchemed.5b00542