Atomic Models

WHAT TO DO

1. Pour enough of the small candies into the bowl to cover the bottom with one layer of candy. Each small candy represents one small atom. Do you see any patterns?
2. Gently shake the bowl from side to side and watch how the “atoms” move. Keep shaking until all of the atoms line up in straight lines. Do any of the rows go all the way from one side of the bowl to the other? What happens at the edges?
3. Add the larger candies—approximately ¼ the number of small candies. Each large candy represents one large atom. Use your hands to mix up the balls and distribute the larger ones throughout. Again, gently shake the mixture back and forth and watch what happens to the atoms. Can you get them to line up again? What happens if you add even more of the larger balls?

Cleanup: You can munch on your candy or reuse the ball bearings for another purpose.

WHAT’S HAPPENING?

Everything around us is made of tiny building blocks called atoms – so tiny a powerful microscope is needed to see them. Scientists create bigger models of things we can’t see to help us understand how those things work. The different candies you used in this activity represent the atoms that make up all materials, and the model you made actually shows some of the same patterns and structures that you would see with a microscope.

Just as you added energy by gently shaking the bowl, materials scientists add energy (heat) to atoms to make them line up into an orderly structure. This is how atoms are arranged in a section of a typical metal. You may have noticed some boundaries where the candies on either side of the bowl line up in different directions. These boundaries are the edges between different crystals in the metal—defects in the structure where the material loses energy.

When you added the larger candies, you created a mixture similar to an alloy, a combination of metals that contains atoms of different sizes. The larger atoms break up the regular structure of the smaller atoms and the boundaries between crystals. These different arrangements of atoms can lead to some very different behaviors of the materials at a large scale.

SO WHAT?

Crystals can have atoms arranged in a very ordered structure, like the balls that were originally resting at the bottom of the bowl. This is called a crystalline structure. Or the arrangement can be disordered due to defects in the pattern or different types of atoms. This is called an amorphous structure. Defects in crystals aren’t necessarily a bad thing—they actually determine how different materials act or behave in our daily lives. For example, a baseball bat made with an amorphous metal is stronger and transfers more energy back to the ball because of how the atoms are arranged, but it is more costly than a standard bat. And stainless steel, which is made of disordered crystals, is a poor conductor of electricity while pure copper and pure silver, made of more ordered crystals, are much better conductors of electricity.

Scientists observe the atomic crystal structure of materials to determine how the materials will behave in the world. They can look at materials up close—even at the atomic level—using a high-resolution electron microscope. However, using this technology is very expensive and takes a long time compared to using other techniques. This technology can also be dangerous; it uses a very high voltage and emits X-rays, so they are built with many safeguards in place.

Scientists In Action For scientists Nasim Alem and Ritesh Uppuluri, microscopes gave them their first peek into a world that’s too small to see with our eyes. What can they discover by looking at tiny patterns of atoms?