During our first fellows workshop, the first cohort of VIPEr fellows pulled together learning objects that they've used and liked or want to try the next time they teach their inorganic courses.
The guided reading questions may be graded using the answer key.
These questions have not yet been assigned to students.
Guided reading and in-class discussion questions for "High-Spin Square-Planar Co(II) and Fe(II) Complexes and Reasons for Their Electronic Structure."
1. Bring together ligand field theory and symmetry.
Students should be able to identify symmetry of novel molecules in the literature.
Students should be able to explain d-orbital ordering in a coordination complex using ligand field theory.
Students should be able to identify donor/acceptor properties of previously unseen ligands.
Students should be able to apply your knowledge of electronic transitions to the primary literature.
Students should be able to become more familiar with 4-coordinate geometries.
Students should be able to predict magnetic moments of high-spin and low-spin square-planar complexes.
Students should be able to identify properties of ligands that favor formation of the highly unusual high-spin square planar complexes.
2. Students should comfortable with reading and understanding primary literature.
You do not have to assign all of the guided reading questions at once. You may consider assigning questions as they pertain to where you are in your inorganic chemistry class.
Do these students identify the same colors as the students without visual impairments?
Are their lab results correct?
Students were able to accurately describe colors.
I have had some students in class have a hard time identifying colors (flame tests, solution color, acid-base indicators, etc.) because of a visual impairment. There are many cell-phone apps that are helpful in aiding these students. "Pixel Picker" allows the students to load a picture from a device (cell phone, ipad). This is helpful because students are now dealing with a "frozen" image. Moving the cross-hair to different parts of the picture changes the R-G-B values. The "Color Blind Pal" app uses a more qualitative approach. It names the color in the cross-hair using various color scales. There are also different options for different types of color blindness.
Both of these apps are free and availble in the App Store.
A student should be able to correctly identify an unknown metal by the color of its flame.
A student should be able to correctly identify the endpoint in a titration by the indicator's color change.
A student should be able to correctly describe the physical properties (color) of a sample.
A student should be able to correctly predict the visible absorbance spectrum of a solution based on correctly identifying the color of the solution.
Have the students with visual impairments practice using the app ahead of time to better prepare them to use the app for the first time in class/lab. Students would also need to understand the additive nature of light colors. For example, high R and G values will appear yellow/orange. I would give these students a 1-page handout for their lab notebook with the addative color wheel and various colored circles labeled with their names and RGB values so that students could practice and reference in the lab.
Our lab safety contract actually has students indicate whether they are color blind. This is a good time to introduce these students to the apps.
This exercise usually takes longer than a 50 minute class period. Students record their answers directly onto their handouts, and I collect the handouts at the beginning of the next class.
Some common student struggles:
In Exercise 2, students don't always understand how to use simple electrostatic arguments to explain the possible packing of benzene molecules in the solid.
In Exercise 3, students are confused by the fact that the PM3 and DFT calculations give them different answers.
In Exercise 4, students find it challenging to sketch how the HOMO and LUMO come together in the Diels-Alder reaction.
This is the sixth in a series of exercises used to teach computational chemistry. It has been adapted, with permission, from a Shodor CCCE exercise (http://www.computationalscience.org/ccce). It uses the WebMO interface for drawing structures and visualizing results. WebMO is a free web-based interface to computational chemistry packages (www.webmo.net).
In this exercise, students perform molecular orbital calculations, which generate electron densities, electrostatic potentials, and reactivity indices. They compare electron distribution in H2, HF, and LiH. They learn about electrophilic and nucleophilic reactivity indices. They use HOMO and LUMO shapes and energies to predict reactivity in a Diels-Alder reaction.
The exercise provides detailed instructions, but does assume that students are familiar with WebMO and can build molecules and set up calculations.
After completing this exercise, students will be able to:
- Calculate and visualize electron densities, electrostatic potentials, HOMO/LUMO, and reactivity indices.
- Use these visualizations to predict or understand reactivity.
Students need access to a computer, the internet, and WebMO (with Mopac and Gaussian).
I use this as an in-class exercise. Students bring their own laptops and access our institution's installation of WebMO through wifi.
In Exercise 1, students compare the electron density distributions in H2, HF, and LiH. It is not always obvious to them that these can be considered models for covalent, polar covalent, and ionic bonding, so I debrief those concepts after they have completed the exercise.
In Exercise 2, students compare electron density distributions in benzene and pyridine. Although they have studied aromatic compounds in organic, they are still somewhat surprised by the benzene results, with its negative region in the middle of the ring and positive region around the outside of the ring. They are reluctant to suggest T-shaped packing in the solid state.
In Exercise 3, students are introduced to the concept of reactivity indices and asked to consider the "Electrophilic (HOMO) Frontier Density," which is used to predict where an electrophile might attack. There are several interesting discoveries for students here. First, they are happy to see that the methoxybenzene calculation predicts an ortho, para preference for electrophilic substituion, which is what they learned in organic chemistry. Second, they see that semi-empirical calculations can sometimes be misleading, when their PM3 thiophene calcuation gives them the "wrong" result, but a DFT calculation gives them the "right" result. The DFT calculation clearly predicts that electrophilic subsitution is most likely at the alpha-carbon atoms. (The PM3 calculation gets the "wrong" order for the HOMO and LUMO, so the electrophilic (HOMO) frontier density ends up on sulfur instead of on the alpha carbons.
It is worth mentioning that the WebMO colors for the electrophilic (HOMO) frontier density may seem counterintuitive. We are used to visualizing electrostatic potentials, where red means negative and blue means positive. Intuitively, we might think that the site for electrophilic attack would be red because it is electron-rich. However, it is blue.
In Exercise 4, students visualize the HOMOs and LUMOs for the diene and dienophile in a Diels-Alder reaction. This exericise takes students longer than you might think. First, they must figure out which orbitals are the HOMOs and LUMOs, by looking at the long list of orbitals and finding the last full one and the first empthy one. Also, it is difficult for them to visualize/understand the orbitals and twist the molecules into useful views.