# Legos, or something like them

Today I ventured yet again into the world of SCALE-UP classrooms. This time with a bit of success! The professor that teaches the class I help out with talked for a while about crystal structures – simple cubic, body centered cubic, and face centered cubic.

The structure of how the material was presented itself went a little bit like the following:

• Introduce the concept that atoms pack together
• Speak on the three main cubic crystal types: SC, BCC, FCC
• Figure out coordination numbers and “n;” how many full atoms belong to a unit cell
• From the above, do theoretical density calculations
• Build ball-and-stick models to look back at the prior items discussed.

In hindsight (isn’t it beautiful?!) the order should have been a little bit different, and I think will wholly influence what we do going forward with models and hands-on activities.  Distribute materials early on so students can manipulate them and practice ALONG WITH the lecture rather than practice AFTER the lecture.  Specifically these 3D style models a few students struggled to see it right away. I think they would have benefited to look at the models with the lecture as opposed to after.

I’m intrigued to see, going forward, what happens when we give out materials early on during a lecture. I can see (as I know I would have been this type of person!) how it would be tempting to play with “toys” and not pay attention. The balance between the two is going to be the most difficult part to manage.  Do you give students hands on examples early and let them tinker at the expense of their full attention? Or does that tinkering immediately instead keep their attention for longer periods of time?

[SCIENCE CONTENT, STEER CLEAR]

I learned a few things that some people struggle with and yet I take for granted.  First off, seeing how a unit cell clips spheres into eighths comes naturally. To some people, it doesn’t. I made this little doodad in Mathematica to illustrate it for a few students and it seemed to help them out quite a bit.

A bit of fun on-the-fly learning happened, too.  As I was teaching them that no matter what atom you are in a crystal structure you see the SAME crystal structure all around you. If we start out with just the center atom of a BCC crystal other center-BCCs would make their own cube with a previous corner as their center-of-cell.

BCC structure with blue at the body center

BCC structure with yellow at the body center

Still a BCC structure. Notice the lower left corner of the yellow unit cell functions as the body center atom of the blue while the upper right corner of the blue unit cell functions as the body center atom of the yellow.

Anyway, that was pretty mindless rambling, but what we discussed in class today. FCC was very difficult to construct and didn’t really teach much – it looks more like a mess than anything.  I’d stick to BCC in the future.

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