In the past four weeks, our time in lecture has been spent bridging the gap between principles (general chemistry) and preparing for the first exam. One topic that has a recurring theme between the two is hybridization. I have noticed two major groups of students: (1) those who need review, and (2) those who are new to the topic. Regardless, I know that, as instructors, it is our job to meet the needs of all types of students.
To start our discussion of hybridization, I talk about how chemistry is meant to be intuitive. I mention the difference between atomic and molecular orbitals, and I try to incorporate as many visuals as possible. I mention the combination of colors to show the distribution of electron density. Thus, when we put 4 AOs in, we get 4 MOs. Because students can struggle to see the difference, I often draw out the s and 3 p orbitals and then follow with the hybridized orbitals of sp3. In the images, we can see that the amount of purple is dramatically different. I appreciate that the Karty text blends the colors together. And, as an additional visual for my students, I also describe mixing Sprite and Pepsi together and refer to this blog post.
Once the initial topics are mastered and it comes time to review the pi system, the idea of pi overlap can throw a wrench in students’ learning of MO theory. Their minds become flooded with an array of questions, such as: “Where does the overlap occur? Just on the top? Just on the bottom? What atom holds the p orbital?” So I employ visuals again to clearly show the distribution of purple that needs to change in the hybridized orbitals. Upon showing these drawings, I build models with balloons, which were inspired by this paper on MO theory and chemical education. Those in the chemical education field are already familiar with the use of long, tube-like balloons to show the sigma and pi frameworks collectively. My students, in particular, are relieved to work with the balloons, as they help them better understand a topic that is quite abstract and hard to contextualize.
Additionally, I use different colors to show the different MOs (sp, sp2, sp3). For an sp2, I use three similarly colored balloons. They show the repulsion and sterics of the MOs and the space that is available for the p orbitals. When my students struggle with how to see the unused p orbital as the p orbital, I use my water bottle and coffee mug to put on a classroom demonstration. I place the set of three balloons on top of my water bottle and hold my coffee mug to show the representation of the p orbital, specifically the lobe that sits above and below the sigma framework. This activity helps my students visualize these orbitals better.
Although MO theory can be challenging for students, I’ve found that the use of models to teach orbitals helps ground these topics with more concrete visuals for students, especially when dealing with tricky pi bonds. How do you like to tackle MO theory in class? Are there any visual aids or insightful examples that you use to facilitate your students’ understanding of these concepts? If so, please feel free to share them below, as I’m always looking for more ways to be more innovative in the classroom!
-Kerri Taylor, Columbus State University
Feel free to share your thoughts in the “Comments” section below!
