Ruby is a crystalline form of Aluminium Oxide

A crystal or crystalline solid is a solid material whose constituent particles (such as atoms, molecules, or ions) are arranged in a highly ordered structure

How do you know when a substance is crystalline?
Metal Crystals

Bismuth Crystals.

Metals will form  crystalline structures because their atoms can bond together in a highly organised fashion

​Crystals can form when a molten solid cools and solidifies. They can also form when a saturated solution is cooled. This happens because the solubility of most solid solutes  decreases as the temperature is lowered. 

The solute can no longer stay in solution and therefore forms a solid precipitate. The precipitate can be crystalline.

Crystallisation can therefore be used to separate a solid solute from its solvent.

Pure crystal 

Task 1
Watch  the video and answer the following:
  1. When recrystallising in order to purify a solid, how much solvent is used
  2. There is a mistake in the apparatus set up at the beginning of the video. Describe the mistake and explain why it would be dangerous to heat the apparatus as shown.
  3. Explain why the filter funnel is heated by a hot water jacket?
  4. Why do crystals then form in the filtrate?
  5. How are these crystals then separated?

The crystals obtained this way can then be dissolved and recrystallised to improve the purity further.​

Crystallisation close up 

Task 2

This video helps you to visualise how molecules ( or atoms) can stick together to form an orderly arrangement and therefore form crystals.

  1. What shape is used in the video to represent the sugar molecules ?
  2. The four images below show four different ways of "modelling" the arrangement of atoms or molecules forming a crystalline structure. Consider each model in turn. For each model try to say what is good about it and what might be "inaccurate" about it. This could be presented as a table of strengths and weaknesses.
  3. It is often said that crystallising something slowly will produce lager and more regular crystals. Can you explain this?
Spheres can be used to model the way atoms and molecules might stack together.

In this video you see how scientist use bubbles in a soap solution to model the behaviour of particles in a crystal. 

A paper filter

Filter first  

Filtration is any of various mechanical, physical or biological operations that separate solids from fluids (liquids or gases) by adding a medium ( a filter) through which only the fluid can pass. The fluid that passes through is called the filtrate.

Filtration is a simple technique used  to separate insoluble solids from a solutionSometimes it is the filtrate that we want to isolate ( as in the making of a cup of coffee), on other occasions it is the residue that is left behind in the filter  that is of value.

In the laboratory 

suction filtration

​In the laboratory suction filtration can speed up the process and help to dry the insoluble residue on the filter paper.

Task 1

Make a copy of the suction filtration diagram. Add labels to the diagram to help explain why a vacuum pump is used.

What's the connection?

figure 1
figure 2
figure 3
figure 4

Task 2. Compare the four images above. What is the connection between all four? Which one is the odd one out  and why ?

(Hint: There is more than one acceptable answer - so long as you can justify it..)

Sun and air

​Study the seaside image for a few seconds . Try to describe it:

You might say that the image shows : A calm sea,  clear blue sky, bright sunshine and a perfectly smooth beach.

You could describe it in terms of the states of matter visible:

​SOLID ​Sand
​LIQUID ​Sea
​​GAS​Air 
​GAS + PLASMA​Sun

But as a chemist you might be asked to classify each of these four components as either mixtures, compounds or elements

You might then go further and identify the atoms which are make up each of those components .

This section will help you to do that.

Mixed or bonded?

A mixture
A mixture

MIXTURE : A mixture is made up of two or more components which although mixed together can be separated by physical means. The components are not chemically combined. 

A compound
Pure salt is a compound

​COMPOUND : A compound is always made up of two or more different elements in definite proportions joined by chemical bonds. The elements cannot be separated by physical means

The Dead Sea is below sea level, this means that it does not drain so that although the water evaporates, the salt will stay, this means that the dead sea is a saturated solution

You can see this because salt crystals appear around the shore line.

The oceans become salty for the same reason - soluble salts are washed in to the oceans by rivers. Water from the oceans evaporates - leaving behind the less volatile salts. 

The oceans are not saturated solutions because they are so vast.

The Dead Sea is relatively very small and land locked. 

Evaporation  causes large deposits of solid salt to form around the shore or the Dead Sea 

.The Dead Sea Location