Explore rocks and minerals, discover different forms of carbon, and use lasers to represent X-ray diffraction patterns. Although these materials may look very different, they are all built from the same fundamental building blocks: atoms.
Have a go
In this activity, you can explore rocks and minerals, discover different forms of carbon, and use lasers to represent X-ray diffraction patterns. Although these materials may look very different, they are all built from the same fundamental building blocks: atoms.
What's going on
Everything around us is made from atoms, the smallest unit of an element. An atom has a tiny nucleus made up of protons and neutrons, surrounded by electrons. The number of protons identifies the element, while its electrons determine how it bonds with neighbouring atoms.
The way atoms are arranged determines the properties of a material. By studying these arrangements, scientists can discover more about the natural world and design the materials of the future.
The same atoms, different materials
Carbon can exist in several different forms, known as allotropes. The most common are diamond, graphite and fullerenes. Their different atomic arrangements give them very different properties.
Diamond has an extremely rigid three-dimensional structure, making it one of the hardest known natural materials. Graphite contains carbon atoms in flat sheets that slide over each other, making it soft enough to leave a mark on paper. A single layer of graphite, known as graphene, is very strong and an excellent electrical conductor.
Fullerenes are hollow carbon structures containing different numbers of atoms. Their cage-like shapes make them lightweight and stable. Some fullerenes can even trap other atoms inside them, forming ‘endofullerenes’.
Researchers at the University of Southampton are investigating these unusual structures for applications in nanotechnology, electronics and medicine.
What are crystals
Crystals are highly pure materials. Scientists often use crystallisation to purify mixtures of compounds or help identify them using diffraction methods. A crystal is more specific than a compound simply being a powder or solid. It needs to have a repeating pattern, or lattice, of the molecule in question.
There are many ways to grow crystals, including cooling and evaporation. A common example of crystallisation is growing blue crystals of copper sulphate. This often starts with a saturated copper sulphate solution. Once small crystals start to form, they are collected. More copper sulphate is dissolved in the solution, and the crystals are added again and allowed to grow larger.
Crystallisation also commonly occurs in nature. The vast majority of atoms in solid matter on Earth are arranged in crystalline structures such as silicates, metals or ice. Salt, quartz, diamond and many metals are naturally occurring crystalline materials.
Even if a crystal appears smooth on the outside, its atoms are arranged in a highly organised internal pattern. The way atoms in minerals are arranged controls a material's properties, including its hardness, colour, electrical conductivity and strength.
Seeing the invisible with diffraction
If atoms are far too small to see, how do scientists know where they are?
The wavelength of visible light is thousands of times longer than the distance between atoms, so we cannot see atoms directly using visible light. Instead, visible light can be absorbed, as with paints, dyes or pigments; reflected, as with aluminium or silver; or pass through a solid, as with diamonds or glass.
Because X-rays have wavelengths similar to the gaps between atoms, atoms can act as a grating and spread the X-rays, creating a pattern of spots. This powerful technique is called diffraction. It requires crystals or crystalline samples because the atoms must be arranged in a regular lattice so that they act as a grid. This is similar to the laser passing through the diffraction grating used in the activity.
In the demonstration, a laser passes through a regular structure to create a diffraction pattern. By studying the pattern created by X-rays diffracting through a crystal, scientists can work backwards to determine the arrangement of the structure that produced it.
The same principles behind the laser diffraction patterns used in the activity are applied in modern research laboratories to determine the atomic structures of molecular compounds, materials, proteins and pharmaceuticals.
The University of Southampton is home to some of the most powerful X-ray diffractometers in the UK. It also hosts the National Crystallography Service, where expert crystallographers help UK academics collect diffraction patterns and solve the crystal structures they come from. This gives scientists vital information about the structure and properties of the materials they have made.
Why this matters
Understanding how atoms are arranged allows scientists to explain and predict material properties. It also helps them create new materials with useful properties.
Researchers at the University of Southampton use diffraction and other advanced techniques to investigate the structure of materials at the atomic scale. By learning how atoms are organised, scientists can develop new materials with improved performance for applications ranging from healthcare to sustainable energy.