My Notes
Categories
This is a hands-on introduction to molecular symmetry and point groups. Students are not expected to have any exposure to molecular symmetry before this lab. Students work in pairs to identify symmetry elements in molecules and assign molecules to appropriate point groups.
| Attachment | Size |
|---|---|
| LAB_Symmetry_2023_handout.docx | 51.92 KB |
| LAB_Symmetry_2023_handout.pdf | 158.87 KB |
A student should be able to locate symmetry elements (axes of rotation, planes of reflection, and centers of inversion) in molecules.
A student should be able to predict the movement of individual atoms in a molecule when carrying a molecule through a symmetry operation.
A student should be able to identify all of the symmetry operations that are present in a molecule.
A student should be able to assign a simple molecule to a point group.
One molecular modeling kit/pair of students
I use this exercise during a 2 hr 50 min lab section (my course has both lab and lecture linked), but it is a "dry-lab" experience that could be split over multiple class periods instead.
I begin lab with a short 5-10 minute lecture introducing symmetry elements and symmetry operations. Students work in pairs for the exercise but they each do their own drawings and each turn in their own report. There are a few points where students take a while to puzzle through the exercises. Some students ask for help when they cannot "see" an element immediately. Instead of giving them answers the first time, I will often redirect them or simply encourage them to play with their model more to find the elements on their own.
I walk around and make sure that each partner is able to locate all the symmetry elements on a 3D model for each part (A, B, and C) of exercise 1 before they move on.
When the first group completes exercise 4, I give another ~5 minute mini-lecture to the class introducing point groups and demonstrating how to use the flow chart. I check their answers for parts 5 A–D in class to make sure they are on the right track; I do not check their answers for the rest of exercise 5 until they have turned it in.
I introduce students to symotter.org in class after they complete this exercise as a study tool to further cement their understanding.
Evaluation
They turn in the sketches and answers to the questions posed in each section as a lab report. I grade it using the answer key linked to this LO.
For the past two years, students were further evaluated on their retention of this material using 4 questions on their final exam.
Student grades on the lab report had an average 81% over the past 6 years (~60 students).
Student performance on the four final exam questions had an average of 76% with point group determination being the weakest. (past 2 years, 20 students)