This In-Class Activity is meant to follow up discussions of ligand field theory toward the end of MO theory including the effects of sigma donors, pi donors, and pi acceptors, and how it relates to absorption spectra and observed color of some transition metal complexes. Students have learned crystal field theory and the effects of geometry/symmetry on ∆, then we extend to LFT and how the chemistries of different ligands affect ∆. Specifically, we discuss how sigma donors, pi donors, and pi acceptors (specifically of ML6 complexes) all have different effects on crystal field splitting according to where the MOs fall in energy and how electron filling affects their energies. This activity is meant to tie some practicality and concrete ideas to the concepts of LFT. The activity has students determine the observed and complementary colors of drawings and, with the knowledge that all are Ni2+ with various ligands, assign which ligand corresponds to which color drawing. A YouTube video in which the Ni2+ complexes are made is used as a follow-up/answer key. Accompanying slides are also included.
Since some students may be colorblind, I do this activity in groups and make sure students know any graded work will never rely on their perception of a color; they would always be given a color name or absorption/reflection wavelength or energy for graded work. However, for inclusivity, the Color Blind Pal App linked in the documents allows students who may have trouble seeing color to participate in the activity and see colors as their classmates would.
A student should be able to
- Demonstrate an understanding of how observed color relates to absorbed color/wavelength
- Relate the absorbed color of the complex to the relative ligand field splitting
- Relate the relative ligand field splitting to which ligand is associated with the complex (based on its position in the spectrochemical series)
- A computer with internet access (to access the YouTube video)
- Copies of handout
I have this activity as part of a larger active-learning workbook in my class. I use the accompanying slides to provide answers as students go along (so they have the correct answers before moving on) and have them work on each question in groups for 5-6 minutes before finally playing the video as an "answer key".
This is an informal, ungraded LO that allows me to gauge student understanding of the practical effects of ligand field theory.
I have used this activity once at this point and it seemed to reinforce a somewhat abstract/confusing topic. Students performed well when tested on this material - 70% of students received full points on a related question on the exam following.