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Physical Science: Session 5

A Closer Look: Seeing the Shapes of Particles

Is it possible to see atoms and molecules with our own eyes?

The simple answer is “No.” When we see something, even with a very powerful microscope, what we are really seeing is the light that has come from some source (like the Sun or a glowing filament in a light bulb) “bounced” off the object and entered our eyes. Scientists call this bouncing “diffraction.”

Let's look at an analogy. Imagine you are skiing down a hill and there’s a small patch of snow missing in front of your ski. If you have normal sized skis, you probably won't notice the hole as you ski over it. You would have to have very tiny skis for your skis to be impacted, or to "see," the missing snow.

In this analogy, the skis are light’s wavelength. Visible light has too long a wavelength to effectively interact with individual particles: they are like the normal size skis going over the small hole. If, however, we use light of a much shorter wavelength light, like x-rays, they can, in fact, interact with individual particles.

What is X-ray diffraction?

dna xray
DNA molecule seen through x-ray diffraction.

In this process, x-rays are directed toward a macroscopic object and are diffracted by the small spaces between its individual particles. Depending on the size of those spaces, the x-rays will emerge from the macroscopic object in slightly different directions. If the pattern of these directions is recorded (e.g., with a photographic plate or specialized digital camera), a computer can then reconstruct what the spacing arrangement was. Once the packing arrangement and the spacing are determined, scientists can reconstruct the size and shape of the individual particles.

Since the image we get is not an actual photograph of what the particles look like, but rather a computer-generated model, x-ray diffraction is called an “indirect” imaging method, as opposed to a “direct” imaging method.

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