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May 19, 2023 0    
Electric Crystals, Part 3
How do Crystals get their Shapes?

Students make paper models of crystal unit cells and build a large crystal structure together while reflecting on the role of symmetry in crystal formation. This lesson is part 3 of a 4 part series. 

Approx time: 45 minutes
Things you'll need:
  • Crystal 3D Unit Cell Activity handout found here

    Electric Crystals (Part 3) worksheet found here



    Tape or glue


Step 1

Unit Cell Models

Cut out and assemble unit cell models from paper.

Following the instructions on the worksheet, cut out the unit cell meshes. For video instructions, check out: Exploring Crystal Structure and Symmetry (Part 1). These models will be used throughout the rest of the lesson.

Fig. 1 (Click to enlarge).
Fig. 1 (Click to enlarge).
Step 2

What's a Symmetry?

Definitions of rotational and mirror symmetries.

The worksheet shows some examples of rotational and mirror symmetries. Also, check in with a video where Madelyn explains how to observe the symmetries of our unit cell models: Exploring Crystal Structure and Symmetry (Part 2).

Fig. 2 (Click to enlarge).
Fig. 2 (Click to enlarge).
Step 3

Replace the Unit Cell File Labels

Use observations of the unit cell models to identify lost file labels.

The newest employee at The Crystal Factory lost the labels for two of the unit cell files. Students will identify the symmetries of each unit cell model and fill out tables with the relevant information. They'll use the information they gather to determine the missing labels for the file cards.

Step 4

Build a Crystal

Build a crystal structure from unit cells.

Students will work together (or build more unit cell models, if they're working individually) to create a large crystal structure from their paper unit cells. They'll then reflect on the process of building a crystal from unit cells as opposed to individual molecules. Students can check in again with a video where Madelyn explains how symmetry restricts the ways crystals can form.

Fig. 4 (Click to enlarge).
Fig. 4 (Click to enlarge).
Step 5

Design Challenge

Try to create a unit cell without rotational or mirror symmetries.

Things can go wrong if a crystal doesn't have the proper symmetries. Students are prompted to create a unit cell without the symmetries we discuss in this lesson. The comic gives a hint as to how crystals grow from their unit cells, and the special properties their symmetry imparts!

Fig. 5 (Click to enlarge).
Fig. 5 (Click to enlarge).
Why it Works

Supplemental materials for teachers can be found at the Galactic Polymath website, where you will find information on learning standards and be able to provide feedback on the lesson.

Don't stop here! This is part 3 of a series! Make sure to check out:

What is a Crystal, Anyway? (Electric Crystals, Part 1)

Unit Cells and Their Molecular Building Blocks (Electric Crystals, Part 2)

Electric Crystals and their Broken Symmetries (Electric Crystals, Part 4)

TAGS: #crystal structure    #crystals    #nanostructures    


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