A History of Crystallography – Part Three

Last week, we discussed crystalline structure classifications and the discovery of X-rays and their use in crystallography.

Bragg’s Law and X-ray Diffraction

Imagine you have a laser pointer in a room of spherical mirrors and black walls. Depending on where you point the laser pointer, it will hit the wall in a different position. Knowing the angle you shine the laser pointer and where it lands, you can find the distance between two of the mirrors. Now, replace the mirrors with atoms and the laser with an X-ray, and you have a setup to find the distance between each atom. The formula used to find that distance is called Bragg’s law.

Don’t worry too much about the math—just know that this equation helps us figure out the distance between layers of atoms by looking at how waves bounce off them. It’s the foundation of many techniques that help us figure out structures too small to see.

Electron and Neutron Diffraction

Remember how light can act like a wave and a particle? The same goes for electrons and neutrons. That means we can shoot beams of them at tiny objects, and they’ll diffract—or spread out and create patterns—depending on what they hit. The idea is the same as X-ray diffraction, but using electrons and neutrons instead of X-rays.

Electron Diffraction vs. Neutron Diffraction

Electrons

• Electrons have tiny wavelengths, so they’re great for seeing really small atomic structures.
• We use electron diffraction to study crystals, nanomaterials, and even viruses.
• It’s part of electron microscopes, which can zoom in much more than regular light microscopes.
• The only downside? Electrons are very reactive and have a charge, so samples can be damaged and pictures may be less clear.

Neutrons

• Neutrons are neutral, so they don’t mess with electrons in atoms.
• They’re especially good at spotting light atoms like hydrogen and studying magnetic properties.
• However, you usually need a nuclear reactor or special lab to create neutron beams.

Cryo-Electron Microscopy

Cryo-electron microscopy, or cryo-EM is a method scientists use to look at proteins, viruses, and other biological molecules in nearly perfect detail, without needing to turn them into crystals.

Here’s how it works:

1. Scientists freeze the sample extremely quickly.
2. They shoot electrons through it to get 2D images.
3. Then, computers combine thousands of these images to build a super-detailed 3D model.

Cryo-EM has changed the game. It used to be nearly impossible to see the structure of large, flexible molecules. Now, scientists can see even the shape of individual atoms in a protein. In fact, cryo-EM was so revolutionary, it won the 2017 Nobel Prize in Chemistry.

Why It Matters

These techniques let us:

• Discover new medicines by understanding how viruses and proteins are shaped
• Build better materials by knowing how atoms are arranged
• Understand how life works at the smallest scale

It all starts with waves, patterns, and some clever thinking. Thanks to Bragg’s Law and its family of diffraction tools, we can see the invisible—and that’s helping us change the world.