- Age: 8+
- Time: 20
- (Setup: 5min, Activity: 10 min, Cleanup: 5 min)
- Materials: $8
In this mission, you’ll look at how atoms are put together inside a material, and how that affects its properties. You’ll do this by creating a model made of candy, which will show some of the same patterns a scientist would see with a (non-candy) microscope!
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- What To Do
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What's Happening?
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 or BBs that 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 inside a typical metal. You may have noticed some boundaries where the lines of atoms don’t quite match up because the pattern on one side is shifted or turned compared to the other. These boundaries are the edges between different crystals in the metal— defects in the structure where the material might crack, bend, or corrode (rust). You might also see places where one atom is missing from the crystal pattern.
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 might form their own crystal, or might mix into the smaller ones to break up the regular structure of the smaller atoms. You might even see a few smaller atoms sitting inside a crystal of larger atoms, or fitting into the gaps between crystals of the larger ones. If you add lots of candies, you might see them arrange in several layers, each layer fitting into the one underneath. The picture of the big bowl of BB’s shows some of these layers. These different arrangements of atoms can lead to some very different behaviors of the materials at a large scale.
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So What?
SO WHAT?Crystals have atoms arranged in a very ordered structure, like the balls at the bottom of the bowl after you gently shake it up. This is called a crystalline structure. Most crystals aren’t perfect: they might have a spot here or there that's missing its atom (a vacancy) or has the wrong kind of atom (an impurity). Sometimes two different crystals inside a material point in different directions and don’t match quite right where they touch. If lots of atoms of different sizes are mixed together and cooled quickly before then can get organized, they might form an amorphous structure with no crystal patterns at all.
Defects in crystals aren’t necessarily a bad thing—they actually determine how different materials behave in our daily lives. For example, impurity atoms at the boundaries between crystals can make a metal stronger, or more resistant to rusting. In certain alloys, different kinds of atoms take different places in the crystal and then lock each other into place. These “superalloys” are very resistant to bending – they are used to make the turbine blades in jet engines. Since the energy in a metal tends to be lost at the boundaries between crystals, an amorphous metal can actually be stronger and bouncier than a crystalline one. Scientists and engineers are still trying to figure out what amorphous metals might be good for!
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.
When carbon atoms are arranged in a flat sheet, they form a crystal structure that looks like a honeycomb. This is called graphene. The picture of graphene shown here was taken by Sai Bachu, a student at Penn State University, using an electron microscope. The white line on the image is one billionth of a meter long (a nanometer). The crystal structure of graphene makes it extremely strong: the “carbon fibers” used in sports equipment and airplane wings are made from wrapped-up layers of graphene.
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