Building Model for Projection

Description

Models consisting of pieces of transparent, colored plastic glued to face polarized ring magnets are shown using an overhead projector. By using different arrangements of magnets, the interactions of various arrangements are demonstrated.

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1. Glue a piece of transparency material to each of 12 magnets so that plastic goes on the same pole side, say the north pole. Glue material of the other color to the south poles of 12 magnets.
2. Magnets with opposite colors will attract, plastic-covered-face to plastic-covered-face.
3. The magnets are hard. Place them on the projector stage plastic-side-down to prevent scratching the stage.
4. Place one magnet of each color in contact. Bring up a third magnet. Wiggle the magnets to permit them to find a stable position.
5. Bring a fourth magnet of the predominant color up to the cluster of three. Jiggle to permit the most stable arrangement to form.
6. Bring a fifth magnet of the predominant color up to the four-magnet cluster, and jiggle. Note the stable configuration.
7. Prepare two strings of magnets of alternating color. Try to bring them together with like colors touching. Move them slightly so that opposite colors become nearer one another.

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Name _____________________________ Class _______

Teacher______________________________

DoChem 043 Bonding Model for Projection

Watch the movies, and sketch the stable configuration of each coordination number.

Coordination No.

2

3

4

5

Provide an explanation for the brittleness of ionic compounds.

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Purpose

• To illustrate parts of the valence shell electron pair repulsion bonding model.
• To illustrate the regularity of bonding in ionic solids.

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• overhead projector, screen
• 24 face-polarized ring magnets (Edmund Scientific, Radio Shack)
• 2 10 cm x 10 cm plastic transparencies of two different colors
• glue

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• Prepare the models in advance of class, and permit time (one day) for the glue to dry.

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Teacher preparation first time: 90 minutes

Teacher preparation: 5 minutes

Presentation: 15 minutes

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There are no unusual hazards in this experiment.

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The magnets are hard. Place them on the projector stage plastic side down to prevent scratching the stage. Follow routine laboratory precautions.

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Store materials for use in future years.

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Presentation Question:

• Provide an explanation for the brittleness of ionic compounds.
  • When planes try to slide past one another in a malleable metal, there are no special cases where all of the interactions are repulsive. In an ionic material, however, an arrangement can be reached where all of the positive ions are opposite one another, and all of the negative ions opposite one another. When this happens, repulsion causes the planes to fly apart. This model can be used to account for brittleness in ionic substances.

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• repulsion
• magnet
• magnetic pole
• plane
• valence shell electron
• pair repulsion theory
• bonding shapes

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