Introducing the Quantum Mechanical Model using Photoelectron Spectroscopy

After taking two courses with American Modeling Teachers Association (AMTA) I gained more insight and appreciation for evidence driven teaching. In the AMTA curriculum students are provided ionization energy values to help them construct Bohr diagrams and explain why multiple energy levels are required in the Bohr model.

In years past I have always taught the atomic structure unit separate from the periodicity unit and ionization energy didn’t come up unit the periodicity unit. I made the shift to using ionization energy values during the atomic structure unit last year and it was so helpful in constructing Bohr models and connecting the atomic and periodicity units. My state level classes only briefly discuss the Quantum Mechanical Model of the atom (QMM) by mentioning what an orbital is and that the model is modern and complicated. However, my honors level classes always take a deeper dive into the QMM, approaching the Advanced Placements level of understanding. This year I decided to try to create a lesson that would use evidence to drive the instruction that would allow the students to identify the limitations of the Bohr model and introduce the QMM. Like using the ionization energies to identify energy levels within the Bohr model, I chose to use Photoelectron Spectroscopy (PES) as my evidence.

I used the attached activity as I would a POGIL activity. Students worked in teams of four (with roles such as manager, reader, recorder, and analyst) to complete the activity. At stop signs, the manager would raise their hand to call me over to check their progress. During that check I am looking to make sure they aren’t proceeding through the rest of the activity with obvious misconceptions and I often ask follow up questions about the work they have done so far. If questions are answered incorrectly, we work back through those questions and I ask more questions about the models and their prior knowledge so they can rephrase their answers (I am sure not to give away answers myself). I believe one of the reasons the POGIL activities work so well for me is that I am transparent with my students. I tell them the exact reason why we use POGIL practices and the importance of teamwork and other process skills that are elicited as well as the importance of roles in uniting the team’s efforts.

pes_graph.png

Figure 1: Example PES graph

My students had no prior knowledge about how to read photoelectric spectra and had never seen the graphs in class before (see figure 1). I thought this would be challenging but I was surprised it was not a problem at all. I had never incorporated PES in honors level in other years but I found it to be helpful in the students' understanding and strengthened their graph interpretation skills. As students label the peaks in this activity, I find it really helpful to have students work with the graphs, labeling important parts. That practice helps students break complicated graphs into smaller chunks to make the story of the graph unfold easier.

This activity was followed up with a similar activity comparing Bohr diagrams and QMM electron configurations. I will be happy to share that activity as well in a future post. Feel free to use and amend these handouts and please reach out if you have ideas or corrections! These activities only get better with the chemistry teacher hive mind!

• For more information about POGIL, please visit www.POGIL.org.
• For more information about the Modeling curriculum and courses please visit https://www.modelinginstruction.org/.
• The preview image can be found on Wikipedia Setup of an ARPES experiment. Ponor, CC BY-SA 4.0, via Wikimedia Commons.
• For more thoughts on teaching PES, see Melissa Hemling's post, How I Fell in Love with PES.

Editor's Note: See Kristen's follow up activity, Navigating the Quantum Mechanical Model Using Guided Inquiry.