Sometimes we have a topic that needs a refresh, and I hope when you’re searching for fresh ideas those searches lead you to ChemEd X! What I love doing is taking an activity that is really great, and using it in my own way with a personal twist.
Last year I wanted to add a new introduction to VSEPR. I have always used the PhET Molecule Shapes simulation, which I still love and will always use, but I have noticed that some students need more help with the 3D visualization of molecular structure. I wanted a hands-on way to introduce VSEPR, and I didn’t have enough model kits to do it with pre-made sets. I found a 2016 blog post authored by Lauren Stewart called Geometric Approach to Lewis Structures (please check it out and download the supporting information). She discussed having students derive and build the shapes ON THEIR OWN before teaching Lewis structures. What an interesting idea! Students apply what they already know about how charges interact with each to construct 3D models of molecules.
I decided to try it in my honors classes. It was so successful that I changed my plans and decided to try it in my on-level classes as well! I gave it my own twist by having students immediately use their models as the categories for an inquiry card sort that showed Lewis structures. I also created an extension for my fast finishers: a second card sort with chemical formulas. My vision was to have students explore the 3D structure of molecules by building the structures, then have them match 2D representations (Lewis structures) to the 3D shapes they built. My early finishers could then try to match the formulas to the shapes and Lewis structures. Some of the formulas matched the Lewis structures to give them a way to start to make connections, but other formulas were unique. This progression was designed to have students start to make connections and do some model shifting while searching for patterns that helped them figure out how these models relate to each other.
This combination uses many of my favorite teaching tools: inquiry learning, hands-on models, group work, and card sorts. I love using card sorts as interactive formative assessments (read more about using card sorts as formative assessments from Chad Husting here.) Using a card sort as an inquiry introduction is something I’ve been doing more and more, and I like them as an intro activity to find patterns as much as I like them for formative assessments. Card sorts are engaging for students, they work very well with collaborative groupings, and they allow teachers to give immediate, rapid, specific feedback to students.
During the activity, I had students check each model with me as soon as they finished building it. I had the same results that Lauren described in her post: students pretty quickly got the planar structures, but the transition from trigonal planar to tetrahedral initially threw them off. Once they figured out that they needed a non-planar structure, they were off to the races.
Another way in which I modified Lauren’s activity was to have them use marshmallows and toothpicks to build the structures. Because they were going to sort the cards to match the 3D models, I wanted them to have enough supplies to build and keep all of their models (ideally for two days). Unfortunately, not all procedure modifications work well. The marshmallows were too soft, and I have already ordered bulk styrofoam balls to use with this activity next year.
The card sort and model pairing, on the other hand, worked like a charm! I had students line up the structures they created across the top of their desk and then place the Lewis structure cards in groups under each structure. When they finished sorting, they checked their work with me. I left their correct work in place, and removed the incorrect matches they had made. Almost all of the groups matched the structures based solely on the number of outer atoms. After I removed the incorrect matches, pairs were very quick to see that the structures that they placed incorrectly were those with lone pairs. When talking to them, I used the term electron groups with students, and most pairs were able to correctly match all the Lewis structures to the electron group geometry after 3 rounds of attempts. (Keep in mind they had not been introduced to Lewis structures, bonding pairs, or lone pairs. However we had created dot diagrams with ionic compounds, so they were familiar with the idea that dots represent electrons.)
Most groups used about 30 minutes to complete their five 3D structures, which left 10-15 minutes for the card sort. In my on-level classes, only two or three groups made it to the chemical formula sort, and were unable to make it further than matching the formulas to the Lewis structures before our 50 minute period ended. In my honors classes, more groups reached the formulas sort, and some students were able to begin to make connections that extended beyond just matching condensed formulas to Lewis structures.
I hope sharing my experience with taking an awesome activity and making it my own will inspire you to try your own mashup! I firmly believe that sharing is important, but to really make it run well, you have to make it your own. Happy creating!
Modeling in 9–12 builds on K–8 and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds.
Modeling in 9–12 builds on K–8 and progresses to using, synthesizing, and developing models to predict and show relationships among variables between systems and their components in the natural and designed worlds. Use a model to predict the relationships between systems or between components of a system.