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Silica Tetrahedron Model

Summary:
This activity is an introduction to tetrahedral structures such as the silica tetrahedron. Materials:
  • 6 toothpicks
  • 4 raisins
  • 2 straws
  • 1 paperclip
  • big plastic cup filled with Dawn soap or bubble soap (fill cup with 1/3 dawn soap and 2/3 water)

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Source:
Adapted from Earth Science by Nancy E. Spaulding and Samuel N. Numowitz by Mr. Dave Mastie, Ann Arbor, Michigan
Grade level:
9-12
Time:
10 minutes prep time and 10 minutes class time
Student Learning Outcomes:
  • Students will be able to build and see a 3-D tetrahedron model.
  • Students will understand importance of silica tetrahedron as the building block of the silicate mineral family.
Lesson format:
Demonstration, Hands-on activity

National Standards Addressed:

DIRECTIONS:

  1. Each group is going to build a toothpick and raisin pyramid. First, use three toothpicks to make the triangle base of the pyramid. Toothpicks should be connected with 3 of the raisins (raisins are the vertices of the triangle).
  2. Next, stick one toothpick in each of the vertex raisins in the base triangle so the toothpicks stand upright. Push the three toothpicks which are sticking up to a common middle point and connect them with the remaining raisin. Each group should now have a toothpick and raisin pyramid.
  3. Straighten out the paperclip so that it looks like an "s" when layed flat. Hook the paperclip around the top of the pyramid.
  4. If your cup wasn't filled by your teacher, place the dish soap or bubbles and water in the cup. Using the paperclip as a handle, dip the pyramid in the soap/bubbles. If the soap doesn't cover your pyramid, place a bit more soap or water in the cup.
  5. Take turns using the straw to gently blow "an atom" in the middle of your tetrahedron structure. (By gently placing the straw in the middle of the soap that is clinging to the pyramid structure, and blowing gently with your straw, you should be able to get a small bubble that represents an atom).
  6. Make sure your teacher has seen your silica tetrahedron model with 4 oxygen atoms (raisins) and 1 silicon atom (blown bubble in middle of model).

ASSESSMENT:

Assessment for this activity is informal. It is suggested that the teacher walk around and see if groups have successfully built a silica tetrahedron structure. Use this model as a starter for discussion about silicate minerals or crystal structure.

BACKGROUND INFORMATION:

It's suggested that students work in pairs for this exercise. Though this could be used for a very quick demonstration done by teacher for all of the class to see.

The raisins you use for this exercise can be used over and over again. Just warn your students not to eat any! You can use Dawn dish soap...the liquid that is in kids' bubbles works just as well. You can dilute the soap with water quite a bit to make the soap last longer (try 2 parts soap for 1 part water first, then dilute more if your tetrahedron holds together). Big plastic party cups work just fine for this exercise, but any cup with a wide enough mouth will work such as big yogurt or sour cream containers.

More than 90% of the minerals in the Earth's crust are members of the silicate family. In all silicates, the silica tetrahedron is the basic building block. It is important for students to understand the structure of the silica tetrahedron. The silica tetrahedron consists of 4 Oxygen atoms (raisins) bonded to 1 Silicon atom (bubble blown in middle of pyramid). This exercise allows students the chance to build a model of an extremely abstract concept (even drawing a tetrahedron can be difficult!).

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Last modified October 22, 2003 by Jennifer Bergman.

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