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This project allows you to grow your own crystals using materials found at home or at the supermarket’s baking aisle.
Participants can explore topics related to materials physics, chemistry, and crystallography, and investigate how atoms and molecules arrange themselves in different regular structures.
Gather your materials, put on your lab coat (or apron), and let the crystal-growing magic begin!
Materials Science, Physics, Crystals, Chemistry
Scroll down to read tips for educators.
In this project you will use atoms and molecules as tiny, self-assembling LEGO blocks to build incredibly ordered, large-scale structures. You will investigate how common household materials can be used to produce the most amazing crystal structures, learn about forming hypotheses, and conduct experiments to test them.
You will also have the opportunity to visualise, and even walk among atoms in augmented reality (AR), and build your own models of the atomic structures you produced.
Materials science is the study of materials, their properties, and their applications. One of the most amazing areas of materials science is nanotechnology.
Nanotechnology investigates the properties of extremely small things, down to atoms and molecules, and produces new materials with extraordinary properties.
The properties of a material depend on three things:
In most materials, atoms’ arrangements are without much order. In many cases, they form molecules that are mixed or tangled together in an untidy way.
However, in some very special cases, the atoms are neatly organised, forming units that repeat periodically (kind of like the links of a chain). These materials, with very organised atoms that repeat a well-defined pattern, are what we call crystals.
Crystals can be found naturally in the ground, but most crystals used in scientific research and in technological applications are grown in a lab. When you think about crystals, what do you think of? Maybe diamonds, quartz, or amethyst? Many different materials can form in crystals, including ice, sand, DNA, and chocolate!
Crystals have been used from ancient times for decoration, as a symbol of power and status, and even for their presumed healing capabilities. Today we know that crystals do not have any healing power, but they are still incredibly interesting and useful from a scientific and technological point of view.
Did you know that none of our current technology, computers, cellphones, GPS, spacecrafts would exist without crystals?
Growing the Crystals:
In this project, we will be looking at crystals from a scientific perspective. For example: did you know that the appearance of a crystal is influenced by how the atoms are organised inside the material? If we know how the atoms are arranged, we can know what the shape of the crystal may look like, and vice versa.
The way atoms arrange themselves in a crystal is called a unit cell. This is similar to the links of a chain: you can have lots of links connected to each other, forming a long chain. Each one of those links will be the same as the next one, but you can have chains made out of big links, small links, round-shaped links, square-shaped links, etc. Each of these chains will be different because it is made of different links.
In a crystal, the links are called unit cell, they are groups of atoms arranged in a particular 3D shape, that is repeated over and over. The kind of atoms in a unit cell and the shape of the unit cell have a tremendous importance on the properties of the crystal.
In this project you will be able to build your own 3D models of different crystal structures!
One of the simplest unit cell is called cubic. Our first AR environment, in the next tab, you help you see why this is called a cubic: the atoms actually form a cube.
There are various types of cubic unit cells. In the following tabs, you will get to experience a few of them.
More complicated unit cells
Citric acid, tartaric acid, and sugar have much more complicated crystal structures than salt. They all have crystal structures called monoclinic. For interest, the crystal structures for the two acids have been included in Figures 6 and 7.
On our BIG SCIENCE website you will find cool augmented reality (AR) environments we have designed and build for you. We invite you to use these to help you visualise different unit cells, and explore the world of atoms in a crystal.
These AR environments work alongside with the kits we have mailed you. Here is how it works:
1) First, use the AR with your phone or mobile device to project the crystal unit cell into the real world.
2) Play around with the various AR environments. Try scale the unit cell up and down to the size you like, rotate the structure, or move your device around it to see how atoms are arranged.
You can even scale the unit cell to the size of your room and have fun ‘walking’ between atoms. If you do this, make sure you take pictures of friends and family holding atoms, or even standing inside the unit cells. Be creative here, there will be prizes for the best photos!
3) Once you are familiar with the AR environments, you can use them as reference to build the real-life unit cells, using the kits we mailed you.
Can you notice any difference between the structures of the different crystals?
Using our 3D/AR models, available on the BIG SCIENCE! Website and the build-your-own-unit-cell kits we mailed you, you can put together the real-life unit cells to explore and physically see the difference between each type of structure. This will allow you to compare to the structure of sodium chlorine.
The Sodium Chloride 3D model is made as a scaled-up version of atoms. The model shows that the sodium atoms are much larger than the chlorine atoms.
You can find the AR version of the sodium chloride crystal on the following tabs, and you can use on your phone to project into your environment and walk inside the crystal.
Also, have a look in ‘Tips for Educators’ below for a time lapse of crystal growth and other helpful resources.
SIMPLE CUBIC
In the ‘simple cubic’ structure, the atoms arrange themselves at the corners of an imaginary cube. Polonium is the only element know today, with a simple cubic structure.
Body Centred Cubic (BCC)
In a body centred cubic (bcc) unit cell, the atoms are located at the corners of an imaginary cube, with one extra atom right in the middle of the cube (Figure 3). Iron and tungsten are examples of bcc crystals.
Face Centred Cubic (FCC)
A more complicated cubic crystal is the face centred cubic (fcc) (Figure 4). There are atoms at each corner of the cube as well as in the middle of each of the faces. Aluminium, Copper, and Gold are examples of elements that arrange its atoms forming FCC crystals.
Table Salt
One of the materials that you will be using in this project is table salt. Table salt is chemically known as sodium chloride, and is made out of sodium (Na) atoms and chlorine (Cl) atoms. Its chemical formula is therefore NaCl. Figure 5 shows what the unit cell of table salt, or NaCl looks like. The crystal structure of NaCl is made up of two unit cells put together. Can you identify which kind of unit cells there are?
Need some help putting together the model? Watch our NaCl instruction video:
Now, to make the crystals in real-life!
All the materials used in this project can be bought at the supermarket.
Sodium chloride is the most common table salt used for seasoning, and it’s an important mineral to have in our diets. Sodium is used in our nerve function and for contracting and relaxing muscle fibres.
Citric acid is typically used for making sour lollies and to change the level of acidity in cheese making.
Tartaric acid is commonly used as an additive in wine making.
Sugar is used in many different foods and is one of the largest produced agriculture products in the world.
Definitions
Supersaturated Solution
Imagine you have a cup of tea and you start adding sugar. At first the sugar dissolves very easily as it goes into the solution. As you add more sugar, it might be necessary to stir the tea a bit to get it to dissolve completely.
You can try adding more and more sugar to the tea, and you will find that there is a point beyond which the sugar can no longer dissolve in the tea and remains at the bottom.
At this point your tea has become ‘supersaturated’.
For All Experiments:
Growing Salt Crystals:
Growing Citric Acid Crystals:
Growing Tartaric Acid Crystals:
Making Rock Candy (Sugar Crystals):
1. Collect your ingredients.
2. Combine 80 g or 8 dessert spoons of salt and the 100 ml or ½ cup of hot water. Stir continuously until no more of the salt will dissolve (most of the salt should dissolve, though). This will create a super saturated solution.
To think and discuss:
Why is it better to use hot water instead of cold water to dissolve the salt? Can you think of the mechanism behind this?
3. If you would like to make coloured crystals, you can add a couple of drops of food colouring at this stage.
4. You can use a string, straight stick or just grow the crystal on the bottom of the jar or glass.
a) Using a string: Tie a knot in the middle of the string and attach the ends of the string to a spoon handle, straight stick or a pencil so that the knot is submerged in the salty water, but not touching the bottom of the jar or glass.
b) Using a straight stick: Use something like a clothes peg to keep the stick suspended above the bottom of the jar or glass.
5. Set the jar in a place where it will not be disturbed, and wait for the crystals to form.
6. The crystals should start forming after a couple of hours. If you leave the crystals for longer, the salt crystals will start climbing up the string and onto the edge of the glass.
7. Take photos and try to measure the size of your crystals in the course of a few hours, days and weeks. See if you can follow their growth with photos and measurements.
8. Post photos of your crystals on our forum, and submit your measurements in the “Submit your Data” tab
1. Collect your ingredients.
2. Combine 30 g or 4 dessert spoons of citric acid and the 50 ml or ¼ cup of hot water. Stir continuously until no more of the citric acid will dissolve. There should only be a little bit of citric acid that will not dissolve. This will create a super saturated solution.
3. At this stage, you can add a couple of drops of food colouring if you would like to make coloured crystals.
4. You can either grow the crystals on a string, straight stick or on the bottom of the glass or jar, just like in the salt crystal experiment (Growing Salt Crystals, Step 4).
5. Set aside the jar or glass for a couple of days for the crystals to start forming. The longer you leave the crystals in the jar or the glass, the larger the crystals will become.
6. The crystals should start forming after a couple of hours. If you leave the crystals for longer, the salt crystals will start climbing up the string and onto the edge of the glass.
Tip: If no crystals have formed after a couple of days try adding an extra teaspoon of citric acid to the water.
1. Collect your ingredients.
2. Combine 20 g or 3 dessert spoons of tartaric acid and the 70 ml or ⅓ cup of hot water. Stir continuously until no more tartaric acid will be dissolved. There might be a small amount that does not dissolve. This will create a super saturated solution.
3. At this stage, you can add several drops of food colouring if you would like to make coloured crystals.
4. You can either grow the crystals on a string, straight stick or on the bottom of the glass or jar just like in the salt crystal experiment (Growing Salt Crystals, Step 4). Just make sure the string or straight stick does not touch the bottom of the glass or jar.
a) Using a string: tie string around a small rock to give a larger area for the crystals to grow around.
5. These crystals will grow faster than the ones produced from salt and critic acid. They will start forming in around an hour.
Tip: If no crystals have formed after a couple of days, try adding an extra teaspoon of tartaric acid to the water.
1. Collect your ingredients.
2. Wet the straight stick (bamboo, skewer, etc.) or string with water and roll it in sugar, to give the sugar crystals something to form on.
3. Combine 125 ml or ½ cups of hot water and the 340 g or 1 ½ cups of sugar. Stir continuously until no more sugar will be dissolved. It will get harder to dissolve the sugar as more is added. There might be a small amount that does not dissolve. This will create a super saturated solution. Allow this solution to cool for 20 minutes.
4. Add any food colouring (only a few drops), or maybe some flavourings.
5. Pour the solution into a clean jar. Place the straight stick (bamboo, skewer, etc.) or string into the solution about 3 cm from the bottom of the jar. You can use something like a clothes peg to suspend the stick in the jar or tie the string to a spoon.
6. Leave the jar somewhere where it will not be disturbed and cover with plastic wrap or a paper towel. Then wait!
7. You should see crystals forming after 2 to 4 hours. If not, you can try to heat the solution and dissolve in more sugar.
8. The longer you wait, the larger the crystals will grow. Make sure they don’t grow so large that you can’t take them out of the jar.
To think and discuss: What is the weight of your crystals? How would you make larger crystals?
For these experiments, try to form a hypothesis before you start. A hypothesis is a prediction or a guess on what you think will be the outcome of the experiment. Once you have completed the experiment, you can see if you were right or wrong, and why that might be the case.
Have a look in ‘Tips for Educators’ below for a time lapse of crystal growth and other helpful resources.
If you were to place one of the crystals that you have grown in a non-saturated solution or water, what would happen?
1. Think about what will happen and form a hypothesis.
An example of a hypothesis could be: “Nothing will happen and the crystals will keep on growing.” Or “The crystals will dissolve into the solution.”
2. Try placing a crystal that you have grown in a glass of water.
What happened? Does this fit with your hypothesis? Does the same thing happen with the other types of crystals that you have grown?
If you were to remove one of the crystals that you have grown from the super saturated solution, what would happen?
1) Think about what will happen and form a hypothesis.
2) Try removing a crystal that you have grown from the solution and let it dry.
What happened? Does this fit with your hypothesis? Does the same thing happen with the other types of crystals that you have grown?
Is there a way that you could stop this from happening?
What would happen if you tried to grow the crystals at different temperatures? Do the growth rates change? Do distinct types of crystals form if you leave the jar or glass inside the fridge, rather than on the table or bench?
1) Think about what will happen and form a hypothesis.
2) Try placing the jar or glass in the fridge and see if you notice any changes.
What happened? Does this fit your hypothesis? Does the same thing happen with the other types of crystals that you have grown?
Head to the forum to find out when we’ll start running this experiment. In the meantime, you can get your materials together.
Gallium Oxide
The gallium oxide (Ga2O3) AR model below has green spheres that represent Gallium (Ga) atoms. You can see that there are two shades of Ga: the dark green and the lighter green.
If you look carefuly you will see that each dark Ga atom is connected to six O atoms, so its coordination number is 6.
The light green spheres are also representing Ga atoms, but each of these is connected to four O atoms, so its coordination number is 4.
So even though there are multiple Ga atoms in the material, there are two ‘kind’ of Ga: those connected to six O and those connected to four O. This is very important when studying the electrical properties of the materials.
Have a look at the structures and see if you can identify how many different kind of atoms are there in each material.
If you have patience: can you determine the coordination number of each kind of atom?
Here are some suggestions and ideas that you might want to consider when planning your approach to this project.
Depending on the level and time, it may be worth discussing some of the following with your learners. This could help extend their knowledge and lead to further discussions.
Crystals in these experiments start to form as the water is evaporated. The salt crystals form through ionic bonds, where electrons are shared between each atom. The citric and tartaric acid produce crystal structures that are complicated and look impressive when grown.
There are several crystal growing competitions, including one run by the International Union of Crystallography (IUCr). This involves creating a video about the crystal growing process.
Here are some additional resources could be helpful:
This is a link to a good video from Ted-Ed that explains crystals in a scientific view, explaining how the atoms join to form different structures.
Here is a time-lapse video of salt crystals forming from the evaporation of salt water.
Here are a couple of links to videos of crystals grown using other materials, such as copper sulphate.
Here is a time-lapse copulation video of several different types of crystals growing.
There is a large amount of crystal growing time lapses on YouTube using many different materials.
Here is an impressive example of crystals growing in nature.
There is a video that can be provided of how to put the sodium chloride crystal together if you are having trouble.
There is an ACS (American Chemical Society) article on the science of candy making that describes how different sugar crystals can make different types of candy. “The Sweet Science of Candymaking” by Tom Husband.
