We do not cover extended solids (solid state materials) in our general chemistry program. With the exception of students who have taken a course in materials science, Inorganic Chemistry I is the first time our students have encountered solid state structure. Although they have built some visualization skills by working with molecules and symmetry, they do not have robust 3D visualization abilities and have trouble using the language of solid state chemistry (unit cells, packing, filling holes, coordination number, etc…) in the context of structure.
There are many excellent activities to help students develop these skills and I’ve customized an activity for my own class. I like having students use multiple representations, so we work with ICE Solid State Model Kits and DAE files (3D visualization that can be done on a smartphone or tablet device). I like using visualization tools that students can use individually so they can look at solids in a way that make sense to them.
The attached file is the activity that I work on with my students. Students should complete this activity in groups during class time.
A student will be able to…
- use alternate representations of extended solids to better visualize solid state structures;
- describe primitive / simple cubic (sc), hexagonal close packed (hcp), and cubic close packed (ccp) lattices in terms of packing and holes;
- calculate the number of atoms in a unit cell and the stoichiometry of a solid;
- calculate the coordination numbers of atoms and ions in solids;
- draw plan diagrams;
- determine the types of holes in sc, hcp, and ccp lattices;
- use ionic radii to predict lattice (close packed) ions;
- calculate the percentage of holes filled in solids.
Students need smartphones or tablet devices. The DAE files also display on macs; they don’t display correctly on PCs. Students can share devices or use their own. I prefer that students use their own because they can manipulate the structure in the way that they want.
I believe that it’s important to guide students as they explore 3D extended structures. Since there is no lab directly associated with my class, all of our visualization activities are done in a standard lecture room during one or more 50-minute class periods.
I have attached the in class activities that I walk through with my students. Students simultaneously look at the DAE files and models that they have built with ICE Solid State Model Kits. Building the solid state models takes time for inexperienced students, but many students appreciate being able to use in silicio and physical models. I frequently pause to emphasize important points, clarify what students should do, or to have a whole class discussion.
We are not able to make it through all of these activities during class, but after making it through the first 5 parts of this activity, students should have the skills needed to complete this on their own. This will take 3-4 class periods. I think that this activity could be done in a lab.
I collect worksheets at the end of every class to see how my students have progressed using the language of solid state chemistry.
I used the SALG (Student Assessment of Learning Gains) to see how much different aspects of the course help their learning. In 2015 (model kits only) and 2016 (model kits and Studio Viewer), I asked about the gains they made in understanding solid state structures. In 2016, I asked how much the model kits and Studio Viewer helped their learning.
On the end of semester SALG in 2016, I asked students about the solid state model kits and Studio Viewer. “HOW MUCH did each of the following aspects of the class HELP YOUR LEARNING?”
|Solid State Model Kits||Studio Viewer|
|A little help||9%||9%|
The students responded more favorably to the solid state model kits, but 80% of students thought that both the model kits and Studio Viewer provided much or great help.
When I asked students, "As a result of your work in this class, what GAINS DID YOU MAKE in your UNDERSTANDING of each of the following?" about extended (solids) structure, 69% of students reported making good or great gains and 7% reported making moderate gains. Only 2% reported making no gains.