crystals

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Home : 2002 : January : 13

crystals
By Julianne

With fourth grade you should really start a unit on crystallization with knowledge of molecules and atoms. The shape of the individual crystals is based on the shape of the molecule or atom that it is made from. I start
with a look at how different materials fit together. The first two activities explore this idea.
1. Have students make an object using legos. What shape is the object? (square) Why? (because the pieces are all square) Now try to make a round object. Can you do it? (No, not easily) Why? (because the pieces don't connect together to create circular shapes)
2. Have students pour

marbles or BB's into a dish. Watch the pattern they make. You should be able to see a "flower" with six petals and a center. Can you induce the marbles to make a seven petal flower? Why?

Now have the students look at different types of crystals. You can get photos from the Internet or books, or you can gather rocks and substances to look at. I have a nice collection of crystal that I bought at local rock shops. It wasn't expensive and the kids LOVE to handle them. Talk about the shapes of the crystals and have the students draw the shapes and identify how many faces each crystal has.

Finally, you are ready to discuss why crystals form. You can do this by explaining that molecules like to "hold hands". They connect to each other at specific points, like tiny legos and create crystal shapes. Have the students experiment with making crystals using some of the following materials. Dissolve them in very hot water. You can just let the water evaporate and then view the crystals through a magnifying glass, or you can suspend a string in the liquid and let the crystals grow on that.

1. Salt
2. Washing soda
3. Epsom salt
4. Sugar
5. Alum

You can also grow crystals on a piece of glass or plexiglass. Dissolve epsom salt in water. Coat your piece of glass with a bit of liquid soap. This helps the crystal solution to spread. Now carefully pour the crystal solution onto the glass and let it sit in a warm place for an hour or more. The crystals will begin to grow at the edges of the glass almost immediately. You can watch them.

I hope some of this helps you. The reason crystals form under these conditions is that once there is not enough water for the material to stay in solution it begins to link together forming crystals as it comes out of solution. I'm sure there's a more scientific explanation, but that should be enough for fourth graders.