By Zoe Canestra
Year 9 Science 2013
A crystal is a solid which is formed by a consistent pattern of molecules fitted together. The collections of atoms in a crystal are called Unit Cells. Unit Cells are repeated in exactly the same formation over and over through the whole material.
Salts are very good substances for making crystals. Some common examples of these salts are Aluminium Potassium Sulphate, Borax, Sodium Nitrate and Calcium Chloride.
Some examples of crystals in nature are:
Some household items that crystals can be grown from are:
- Table salt
When a salt is in a solution, it is able to move around freely. As the solvent (in this case, water) evaporates the solution becomes more concentrated. This forces the molecules to bond together. In this case, it forms a crystal.
come in all different shapes, sizes and colours. Unit cells can be in all
different shapes, such as cubes. Whatever shape they are, the unit cells
tessellate to form the crystal. The size depends on the concentration of salts
in the solution and also the available space it has to grow. This especially
refers to when crystals grow underground where there is not enough room to grow
evenly in all directions. Crystals can be different colours depending on what
sort of salt you use. For example, using copper sulphate would produce blue
There are four types of crystals. The first is covalent crystals. In this type of crystal, the atoms share electrons which makes them covalent. Therefore, a single crystal is really just one giant molecule. A diamond is a covalent crystal.
The next type is metallic crystals. The individual atoms in this crystal sit in a lattice structure while the outer electrons from said atoms flow freely around the lattice.
Another type is ionic crystals. This kind of crystal doesn’t have covalent bonds joining its atoms, but are instead held together by electrostatic forces. Sodium chloride is an ionic crystal.
The last type is molecular crystals. It has recognisable molecules in its structure which are held together usually by hydrogen bonds. An example of this type of crystal is sugar. This is the softest of the four crystals with a relatively low melting point.
Crystals often have a high refractive index. This means that they are easily capable of total internal reflection. For example, a diamond is cut so that the light is totally internally reflected, but sometimes the light is refracted so much that as some of it escapes the diamond it disperses, splitting into the colours of the spectrum (this is called the ‘fire’ of a diamond). The diagram shows what light does when it hits the diamond at different angles.
For a crystal to its optimum size, there are a few things to know before starting. Firstly, the solution must be super saturated with warm water. This means dissolving as much of your chosen material as you can, and the warm water is so it dissolves faster (because the molecules move more in warm water). After the solution has been made, you must find a place that is warm and light to aid water evaporation. This will make the crystal grow much faster.
Best Crystals for Beginners. (2013). Retrieved from About.com: http://chemistry.about.com/od/crystalsforbeginners/tp/quickcrystalprojects.htm
Crystal. (2013). Retrieved from Wikipedia: http://en.wikipedia.org/wiki/Crystal
Crystals. (2011). Retrieved from Science Kids At Home: http://www.sciencekidsathome.com/science_topics/what_are_crystals.html#more
Growing Quality Crystals. (2010). Retrieved from MIT Department of Chemistry: http://web.mit.edu/x-ray/cystallize.html
Science for Kids: Crystals. (2013). Retrieved from Ducksters: http://www.ducksters.com/science/crystals.php
The Best Growing Conditions for Crystals. (2013). Retrieved from eHow: http://www.ehow.com/list_6621144_growing-conditions-crystals.html
What are crystals and how do they grow? (2012). Retrieved from Royal Australian Chemical Institute: http://www.raci.org.au/document/item/86
What is a crystal? (2011). Retrieved from Kiwi Web: http://www.chemistry.co.nz/crystals_defined.htm
What types of crystals are there? (2011). Retrieved from Kiwi Web: http://www.chemistry.co.nz/crystal_types.htm
Why do different crystals have different shapes and sizes? (2011). Retrieved from Kiwi Web: http://www.chemistry.co.nz/crystals_shapes.htm
Tuesday - Lesson 1
- 25g of potash alum
- 2 x 250ml beakers
- 170ml hot water
- Filter funnel and filter paper
- Watch glass or paper hat to fit onto a beaker
- Glass stirring rod
- Place the potash alum in one of the beakers and add the hot water.
- Stir the mixture with the stirring rod until all the crystals have dissolved.
- Filter the solution through a filter funnel (with the filter paper in it) into the second beaker.
- Cover the beaker of solution with the watch glass or paper hat and set aside to cool.
- Make sure it is in a sheltered place where it will remain undisturbed overnight.
Wednesday - Lesson 2
Overnight, a layer of crystals should have accumulated at the bottom of the beaker. If so, move on to the other tasks. If not, follow the instructions below:
- Add one potash alum crystal into your mixture.
- Cover with the watch glass or paper hat and leave overnight once again.
Or, you can follow this set of instructions:
- Scratch the bottom of the beaker with a glass stirring rod.
- Cover with the watch glass or paper hat and leave overnight once again.
Thursday - Lesson 3
- 2 x 250ml beakers
- Overnight, the bottom should have become covered with a layer of small crystals.
- Carefully pour the liquid that remains in the beaker into a clean beaker.
- From the crystals at the bottom of the beaker choose one good symmetrical crystal to be used as a 'seed' for a big crystal.
- Remove this crystal from the beaker and put it into the jar to take home. Try to put it into the middle.
- Take a picture of the crystal next to a ruler and mark the height of the liquid on the beaker. Record the date.
- Cover the beaker with paper and put it in a safe spot that isn't in direct sunlight or near a heater.
MSDS (Materials Safety Data Sheet)
We made the solutin today, so it was just a completely clear liquid. We left it overnight covered with a watch glass. The photo above is of me filtering the solution through the funnel and filter paper into a second beaker where the crystals will grow.
Today we checked the crystals and they looked great! The were triangular and clear, and much bigger than I expected. I also didn't expect them to be such geometric shapes.
The crystals grew a small amount today, but not much. They grew enough to start connecting to surrounding crystals. Rowina and I took three crystals each and put them into our individual jars to take home. Hopefully we are successful!
Today I set up my crystal in the study. It has a lamp shining 30cm above it, which will remain on until the solution dries up. I have also set up a camera, where I can take a photo from the same place every time of my crystal. I think it will turn out well. Crystals haven't noticeably grown yet.
The crystals have grown a minimal amount, if at all (they look larger in this picture than in the last because of the angle). They seem to have remained the same size as they were when I took them home on day three. Luckily, I have set up a camera to take a photo every day, to more carefully monitor the growth of my crystals. Once the solution has completely dried up, I will know exactly how much progress has been made.
I have set up my crystal with a lamp 30cm above the jar with the filter paper on top, but it does not seem to be doing much, so I have decided to take off the filter paper and lower the lamp to 5cm above the top of the jar. Let's hope this speeds things along a little!
Good news, the crystals have grown much bigger! Moving the lamp closer the jar has proved very effective. The crystal is steadily growing bigger and the solution level is steadily getting lower. I predict they will be completely dry in a few more days.
The solution of my crystal totally dried up on Day 21, leaving five crystals; two large ones, two medium ones and one very small one. The crystals grew very fast in the first and second day, going from an empty solution to a solution filled with crystals. But when I took them home on the holidays, the growth slowed to a crawl, growing remarkably slowly. I decided to take a chance, a lowered a lamp over the jar to heat up the solution. After doing this, the crystals grew better and more steadily, and after approximately one more week the solution had completely dried up and all that was left was the five crystals. The sizes were:
Crystal 1: Largest of the five, 7mm high, 23 mm long, 16mm wide
Crystal 2: Second largest, 7mm high, 19mm long, 15mm wide
Crystal 3: Medium sized, 8mm high, 16mm long, 10mm wide
Crystal 4: Medium sized, 6mm high, 13 mm long, 11mm wide
Crystal 5: Smallest crystal, 3mm high, 6mm long, 5mm wide
The above photos are of two of the crystals mounted on a torch to observe how the light behaved within them. They are very irregular shapes, so the light made it look like the crystal glowed. Some light escaped and could be seen on the ceiling (the torch was pointing upwards) with the shadow of the crystal in the middle. No light was dispersed, just internally reflected. The third photo is a table showing the liquid levels and crystal height with date and time.
Below is a video I made of my crystal growing. It is a good representation of what I said earlier about the growth being slow at first and then speeding up.