2 Apr 2008

Solid-state model building exercise

In-Class Activity

Submitted by Joanne Stewart, Hope College
Categories
Prerequisites: 
Corequisites: 
Course Level: 
Description: 

Students construct models of ionic solids in class and answer a series of questions about the structures.

AttachmentSize
Microsoft Office document icon ionicmodelsexercise1-1.doc31.5 KB
Learning Goals: 

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.

Equipment needs: 

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.

Implementation Notes: 

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.

Time Required: 
50 minutes in class to provide instruction on how to build models, have pairs of students build one model, and have students begin to answer worksheet questions. Students come in outside of class to look at models and answer remaining questions.
Evaluation
Evaluation Methods: 

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.

Evaluation Results: 

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.

Creative Commons License: 
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