Flipping Molecular Structures
Science Teacher, Vista Ridge High School,
Colorado Springs, CO
The flipped classroom model often starts with replacing whole-class lecture time with traditional homework and using video podcasts to get the notes done in the individual learning space.
Few teachers who flip their classes successfully stay in this mode for very long. Once the lecture is moved out of classroom time and space, it leaves a void. Teachers can be more focused and intentional about how to get the most learning accomplished during these precious moments of face-to-face time with students. Sometimes that means solving homework problems, but it can also involve labs, demos, and inquiry-style investigations that help make learning more meaningful and long-lasting.
Building basic molecules
One approach in particular that has benefited my students tremendously is to start off the unit about chemical bonding and molecular structures with a guided inquiry-style activity called Balloon Geometry.
Working in small groups of 3 or 4, equipped with a set of 8 balloons1, a ball-and-stick or space-filling model kit, and a camera (usually a smartphone), students build models of the simple molecules CH4, NH3, H2O, and HF. As they work to describe the geometry and bond angles, the teacher is free to move around and interact with each team to watch for misconceptions.
After building the molecules, each group compares their results, and the teacher leads a discussion about the impact of lone pairs on bond angles. This is where a little planning comes in:
- One team has 4 balloons of identical color, and they will be chosen to discuss the CH4 molecule.
- The next team has 3 balloons of identical color and 1 that is different. This team is selected to discuss the shape of the NH3 molecule with a lone pair.
- For the H2O molecule, the next team has 2 of each color.
- Since the HF molecule has 3 lone pairs, the final team should have 3 identical balloons and 1 of a different color.
From this foundation, it’s easy to introduce hybridization since all of the molecules in this discussion have sp3 hybridization but result in very different molecular shapes.
From there, introduce other electron domains including those with an expanded octet and launch into discussions of symmetry, polarity, intermolecular forces, and so on. The lesson can be modified for first-year chemistry or biology, or it can be scaled up to the honors level.
This lesson provides a great opportunity for students to critique the advantages and limitations of a particular model as they compare balloon models to ball-and-stick models to Lewis structures drawn on paper— especially when dealing with multiple bonds, resonance structures, formal charge, and polyatomic ions. It’s important for students to grasp that every model has disadvantages.
At the end, students summarize their results by sharing their photos and sketches to a Google doc or sheet that they copy to their digital lab portfolios. Here are a few examples of what students have created to showcase their work.
Student collaboration is key to building understanding and reinforcing class culture as they each contribute to the document, comment on each other’s work to ask for clarification, and improve their overall results.
Enhance the lesson with flipped instruction
Discussions of abstract concepts take time, and in a traditional class, they might be rushed. In a flipped classroom, the detailed instruction about the process of drawing molecular structures can be moved to video podcasts created or curated by teachers and/or students.
My YouTube playlist AP Chem Bonding includes instructional videos I created specifically for my class, as well as crash course videos related to this topic.
After students work through this online content at a time and place of their choice, they are then able to come back to class to practice drawing structures, build models, and refer to their balloon models now on display in the classroom. The guided inquiry experience enhances the online content, and the instructional videos provide more details about valence-shell electron-pair (VSEPR) theory, bonding, and bond energies.
Since class time is no longer devoted to taking notes, we have more time to work through complex topics using modeling and inquiry. Flipped learning strategies allow the inquiry to occur at any point in the process—as an introduction to a concept, an enhancement, or a summary—so that the meaningful activities taking place in the classroom strengthen student understanding.
1 Mini Mylar balloons work nearly as well as latex balloons. Also, the Mylar balloons have a little pocket that fits neatly over the end of a stick from your molecular model kit so it can be used to represent the lone pair in any molecule.