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May 18, 2023 0    
Electric Crystals, Part 2
Unit Cells and Their Molecular Building Blocks

Through hands-on activities using gumdrops and toothpicks, students will learn about unit cells that make up the repeating structures of crystals like table salt. This lesson is part 2 of a 4 part series. 


Approx time: 45 minutes
Things you'll need:
  • Electric Crystals (Part 2) worksheet found here

    Supplies per student per unit cell:

    • 42 Toothpicks
    • 14 of gumdrop/grape (color 1)
    • 14 of gumdrop/grape (color 2)
Step 1

The Unit Cell

Meet the most basic building block of a crystal.

Read the first page of the worksheet to learn that unit cells are the building blocks of a crystal. They can't be divided any farther, or they won't grow into a full crystal. However, unit cells contain lots of molecules and atoms inside them.

Vocab
unit cell: the smallest possible piece of a crystal

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

Activity Prep

Assemble your supplies for the molecule-building activity.

Each student should obtain 14 gumdrops or grapes of each color, as well as 42 toothpicks.

Step 3

The Parts of an Atom and Ionic Bonding

Background about some super cool chemistry stuff.

Panels on the worksheet define the parts of an atom-- protons, electrons, and neutrons-- and the concept of electron shells. The process of ionic bonding is also introduced, and students are guided through some comprehension questions to solidify their understanding of these definitions.

Vocab
proton: positively charged particle
neutron: neutrally charged particle
electron: negatively charged particle
nucleus: center of an atom where protons and neutrons are found
shell: different energy levels of the electron cloud surrounding a nucleus

Fig. 3 (Click to enlarge).
Fig. 3 (Click to enlarge).
Step 4

The NaCl Unit Cell

Using toothpicks and gumdrops or grapes to build molecular models and a unit cell.

The worksheet guides students through building four NaCl molecules to start, then the process of connecting the molecules together to begin forming a crystal structure. The symmetry rules of the chemical bonds are summarized, and students are prompted with several comprehension questions on these rules. Students finish building an entire NaCl unit cube, and reflect on its shape and usefulness.

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

Covalent Bonding

Introduction to the more complicated bonds in SiO2 molecules.

Panels on the worksheet introduce the concept of covalent bonding, then explain that the chemical bonds inside SiO2 molecules are more complex than those in NaCl.

Step 6

(Bonus Challenge: Building SiO2 Molecules)

Using toothpicks and gumdrops or grapes to build molecular models.

More advanced students might enjoy the challenge of building several SiO2 molecular models then attempting to fit them together as a unit cell.

Fig. 6 (Click to enlarge).
Fig. 6 (Click to enlarge).
Step 7

The SiO2 Unit Cell

Diagrams of the SiO2 unit cell.

Projections of the SiO2 unit cell are discussed to lay the foundation for concepts covered in P4. Students can also explore a 3D model of the quartz unit cell, and notice that viewing the cell from different angles produces different projections.

Fig. 7 (Click to enlarge).
Fig. 7 (Click to enlarge).
Why it Works

Supplemental materials for teachers are on 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 2 of a series! Make sure to check out:

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

How do Crystals get their Shapes? (Electric Crystals, Part 3)

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


TAGS: #crystal structure    #crystals    #nanostructures    
 
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