Dorothy Hodgkin looked at how atoms fit together into very complicated molecules. She used X-ray crystallography to find out what penicillin and insulin look like. Knowing what the molecules look like has helped other scientists understand how these molecules work, and to make new medicines.

How hard can it be to make a crystal?

You will need...

150 grams of sugar
50ml of hot water, plus extra for heating
A spoon
A cloth, tea towel, or something similar for keeping your water hot (this is not essential, but it does help).
A pencil
Thread
Paperclip
Two glasses or jars that can hold take boiling water safely
Filter paper or coffee filters

How long will it take?

Setting up the solution will take about an hour and this formula should make reasonably large crystals in about a week.

What to do...

Following the instructions should give fairly good crystals but problems arise if the solution is too saturated, i.e. if the solution has been boiled with the sugar.  The crystallisation starts immediately throughout the liquid and at the surface.  Since there are so many crystals, none grow to any useful size.  At the other extreme is when the solution does not contain enough sugar and no crystals form.  You can suggest adding food colouring to create coloured crystals.

If there are many crystals growing on the side of the glass you can try pouring the liquid into another clean glass.

If no crystals start to form on the thread you can tie a small sugar crystal to the thread to act as a seed crystal.

Answers to fill in the blanks

The sugary liquid is a saturated solution.  When water is hot it can hold more dissolved sugar than when it is cold.  As the solution cools and some of the water evaporates the solution cannot hold all the dissolved sugar.  Crystals start to grow on the bottom and sides of the glass, on the thread and the paper clip, anywhere there is an impurity.  Over time more sugar molecules attach to the crystals and the crystals grow and grow...

 

Curriculum Links

X-ray vision
Science

Chemistry

Pure and impure substances

  • mixtures, including dissolving

Physics

Physical change

  • conservation of material and of mass, and reversibility in dissolving
  • the difference between chemical and physical changes

Particle model

  • the differences in arrangements, in motion and in closeness of particles explaining changes of state, shape and density
  • atoms and molecules as particles

Scottish Curriculum Links

Science

SCN 3-15b

Materials - Properties and uses of substances

Having contributed to a variety of practical activities to make and break down compounds, I can describe examples of how the properties of compounds are different from their constituent elements.

 

SCN 4-15a

Materials - Properties and uses of substances

Through gaining an understanding of the structure of atoms and how they join, I can begin to connect the properties of substances with their possible structures.

 

SCN 3-19b

Materials - Chemical changes

Technologies

TCH 3-01a

Technological developments in society

X-ray vision

X-rays were discovered in 1895 by Wilhelm Röntgen. This discovery earned him the first Nobel Prize for physics - one of the highest awards a scientist can get.  Very quickly, physicists and chemists started to use X-rays to look at the structure of molecules.

sodium chlorideCrystals are special because the atoms that make them up are bonded in a very regular way - see the diagram on the left. A single salt molecule contains one atom of sodium and one of chlorine, but even in a small salt crystal -such as what we put on our food - many thousands of these atoms are bonded together in this pattern.

When X-rays are fired at a large crystal compound such as salt, they bounce off in different directions depending on the type and position of the atoms and molecules inside it.

If scientists wanted to study the properties of an unknown compound, they learned that the compound had to be made into a perfect - and reasonably large - crystal so that all the molecules in it are aligned, and the X-rays bounce off in regular patterns. These patterns could then be analysed so the scientists could find out about the type and structure of the molecules that make up the crystal.

Key fact: When molecules are in the form of a crystal, it allows scientists to discover their structure.

 

 

Sugar crystalsHow hard can it be to make a crystal?

Download the pdf instructions here.

Some materials occur naturally as crystals.  Try to think of all the substances in your home that are crystals.  The two most obvious ones are salt and sugar.  You can grow your own sugar crystals at home by adding sugar to hot water, but it is pretty tricky to make a perfect crystal!

You will need...

150 grams of sugar
50ml of hot water, plus extra for heating
A spoon
A cloth, tea towel, or something similar for keeping your water hot (this is not essential, but it does help).
A pencil
Thread
Paperclip
Two glasses or jars that can hold boiling water safely
Filter paper or coffee filters

Growing crystalsWhat to do...

1.  Heat the water in the kettle, and pour some into one of the glasses to warm it up.  Be careful with the hot water!

2.  Insulate the glass by wrapping a cloth around it while you pour in another 50ml of water.  Then immediately add the sugar all in one go.

3.  Stir, stir, stir, until as much of the sugar is dissolved as possible.  If you can, keep the glass insulated so the water stays warm (but make sure that you have a good hold of the glass through the insulation).

4.  After at least five minutes of stirring, put the filter paper in the top of your second glass and pour in the warm sugar solution.  It should be quite thick, and will take a while to filter through.

5.  Tie the paper clip to one end of the thread, and tie the pencil to the other end.  Roll up the thread on the pencil so the paper clip will dangle in the filtered sugar solution, with the pencil resting across the top.

6.  Leave it like this and wait.  And wait...  Crystals will start to grow after a day or two.  Within a week they can grow large enough for you to see the natural shape of the crystals.

You can try making many other types of crystals.  Salt, alum or copper sulphate can all work well.

 

What is happening?

Take this online quiz to test whether you can explain what happened in the experiment above.