28 Jun 2016

Close Packing Activity

In-Class Activity

Submitted by George Lisensky, Beloit College

Many extended structures can be viewed as close-packed layers of large anions, with the smaller cations fitting in between the anions. Larger holes between close-packed anions can hold cations with octahedral coordination. Smaller holes between close-packed anions can hold cations with tetrahedral coordination. The online jsmol resources show these layers and their holes.

Learning Goals: 

Students will understand octahedral and tetrahedral holes between close packing layers (either hcp or ccp)

Equipment needs: 

A physical model kit such as the ICE Solid State Model Kit (see the related activities) could be used. With the linked web resources for this activity students can display individual layers and the holes between them. Both physical and virtual models are valuable learning tools. Either could be used separately depending on availability but they work together well.

Implementation Notes: 

For cubic close packing

Click on item 1 and click on Spacefill. Click on item 2 and item 4. What is the arrangement of atoms around each other in Pa, Pb, and Pc layers?

Click on item 1, then item 3, then item 5 to stack layers. The image can be rotated by dragging. You can add or subtract layers by backing up a step or going forward. You can switch between Ball, Spacefill, and Translucent representations.

To repeat the sequence, where should the next layer go? Click on step 6.

Step 7 shows that these layers contain a face-centered cube, stacked along its body diagonal.

Similarly you can experiment by filling in the spaces between the layers. Where can you fit tetrahedra between the packing spheres? Where can you fit octahedra between the packing spheres?

Try switching the display to Ball and Stick with Translucent Polyhedra.

A similar procedure can be used to examine hexagonal close packing.

A note about color: steps with color names in them change the color. Other steps do not. For example if you want the layers different colors use step 1, 2, 4, 7; if you want the layers the same color use steps 1, 3, 5, 6.

Time Required: 
30 minutes
Evaluation Methods: 

This has been used by the author to illustrate features of class packing in lecture. 

Creative Commons License: 
Creative Commons Licence

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