My Notes
Categories
Students construct models of ionic solids in class and answer a series of questions about the structures.
| Attachment | Size |
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| ionicmodelsexercise1-1.doc | 31.5 KB |
Students can build a model of an ionic solid that is ccp or hcp anions with cations in the octahedral and/or tetrahedral holes.
Students can describe the solid (using the words hcp, ccp, and octahedral/tetrahedral holes).
Students can determine the empirical formula from the structure.
Students can look at an already constructed model (one that they did not build) and do these things.
Solid state model kits from ICE; at least 1 kit per 4 students. See "Solid State Model Kits" at the bottom of this page: http://ice.chem.wisc.edu/Catalog/SciKits.htm#Anchor-Solid-31140. I use the student version.
I adapted this from an exercise I got from Maggie Geselbracht. I typically have each group build NaCl in class for practice, then I assign them one of the structures on the worksheet, which they build in class. After that, we leave the structures out on a big countertop in the room, with the instruction book open to the appropriate page underneath, so they know which structure is which. Students are allowed to come in on their own time to complete the assignment.
Evaluation
I grade their answers to the worksheet questions, and I develop a test question where students are given a model they haven’t seen before and asked to describe the geometry and give the empirical formula. For the test, I typically use a structure with two cations, such as CaTiO3, because it is a little illustrates more of the concepts and provides a slightly more challenging empirical formula.
The students can easily describe the "standard" structures like NaCl or fluorite, but struggle to describe the layered structures. In particular, if the coordination geometry of the cation is not tetrahedral or octahedral (there's one that's cubic and one that's trigonal prismatic), they're really not sure what to write. Typically, a student will raise a question about these "unusual" cases, and they are discussed on the class discussion board before the students turn in the assignment.