If Lawrence Bragg was still alive he really could be boastful. This November marks the centenary of crystallography. It’s a powerful technique Bragg helped to develop for studying the structure of chemicals.
Born in Adelaide, Lawrence remains the youngest person ever to win a Nobel Prize, the most prestigious award in science. Lawrence was just 25 years old when he shared the 1915 Nobel Prize in Physics with his father William.
Bragg’s work is still important today because it forms the basis of X-ray crystallography, a method for determining how atoms are arranged in a crystal. This kind of structural information is important for developing new technologies such as materials and medicines.
When a beam of X-rays strikes a crystal, the atoms in the crystal cause the X-rays to bend and spread out, forming a distinctive pattern. This phenomenon is known as diffraction and occurs when electromagnetic waves, such as visible light or X-rays, encounter an obstacle or narrow opening.
The resulting diffraction pattern for each substance is unique and depends on the spacing and arrangement of atoms within the crystal. Using Bragg’s famous law, it is possible to interpret the diffraction pattern and determine how the atoms are positioned within the crystal.
Table salt and diamonds were some of the first crystals to be studied by the Braggs using X-ray crystallography. Since then, the technique has been used to study the structure of countless substances. Perhaps most famously, it was used to determine the double helix structure of DNA, the chemical instructions on which life is based.
Understanding the chemical structure of substances helps scientists understand their properties, so it can be an important step in solving difficult problems. CSIRO scientists are using X-ray crystallography to study the structure of a protein found in the brain called amyloid beta. This protein is associated with Alzheimer’s disease, which results in memory loss. Understanding the structure of amyloid beta may help find a treatment for the disease.
So Lawrence Bragg is one person who might deserve to be just a little bit immodest. The method he helped to develop one hundred years ago remains one of the most important and powerful tools for investigating chemical structure today.
Try these Science by Email activities on diffraction
Flexible mesh wide enough to cover the top of the drinking glass
Postcard (or cardboard)
What to do
This activity is best performed outside or over a sink in case of spills.
Pull the mesh tightly over the opening of the glass and secure it in place with one or more rubber bands.
Fill the glass with water by pouring water through the mesh.
Place the postcard on top of the glass of water and push down gently on the card.
While holding the postcard in place, turn the glass upside down.
Carefully let go of the postcard.
Carefully remove the postcard by pulling it sideways (horizontally). Be careful not to shake the glass.
When you remove your hand from the postcard, the postcard should stay on the cup, holding the water inside. Even though the weight of the water is pushing down towards the ground due to gravity, the postcard does not fall because there is air pressure pushing upwards and holding the card in place.
We may not always notice it on an everyday basis, but the air around us is constantly pushing on us and the things around us. This push from the air is called atmospheric pressure. Atmospheric pressure acts in all directions, not just downwards but also upwards against the postcard.
So why does the water stay in place when you remove the postcard? Because water molecules are strongly attracted to each other, the water is able to form a ‘skin’ between the gaps in the mesh. Water molecules at the surface of the water experience an inwards pull due to their attraction to other water molecules. This inwards or contractive pull is known as surface tension and is what causes the water to behave as if it has a skin. The water remains in the cup because the atmospheric pressure pushes against the surface of the water, just as it did on the postcard.
Surface tension is responsible for many aspects of water’s behaviour. For example, you may have noticed water forming spherical beads on the surface of a waxy car bonnet or oily leaf. Since water molecules are attracted to other water molecules more than the waxy bonnet or oily leaf, the surface tension of the water pulls the droplet into a spherical or nearly spherical ball.
Surface tension is also important for soap bubbles made from water and detergent. The contractive pull of water’s surface tension means that free floating bubbles will contract into the shape with the smallest possible surface area per unit volume, a sphere.
1. What is the name given to a predator that sits at the top of the food chain?
2. What is pectin commonly used for in cooking?
3. What is the name given to the deepest part of the ocean in the world?
4. Which chemical element is common to glass, sand, sealants and computer chips?
5. Name a very common substance that is denser as a liquid than as a solid.
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1. A predator that sits at the top of the food chain is called an apex predator.
2. Pectin is used as a gelling agent in cooking.
3. The deepest part of the ocean in the world is the Mariana Trench.
4. Silicon is a chemical element common to glass, sand, sealants and computer chips.
5. Water is denser as a liquid than as a solid.
Dr Denise Hardesty leads a team of scientists, school students and members of the community that has been working along the Australian coastline recording all the litter, or ‘marine debris’ that they find.
Marine debris is a threat to wildlife and through this project Denise and her team hope to better manage the problem.
To learn more about marine debris and what’s being done to address it, go to the CSIRO Ustream channel, and click the links on the right hand side.
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