Molecules

Here are some examples of how atoms and molecules can be arranged:

Crystalline:

In a crystal the atoms are packed into a regular repeating pattern, which gives the crystal its shape. The picture above shows some salt crystsals. Whilst the picture to the right shows how the molecules can be stacked within a typical crystal.

Amorphous (or glassy):

An amorphous solid has no fixed pattern. If you solidify a liquid really quickly there is no time for the atoms to form a pattern. This is why glass has to be cooled slowly to allow crystals to form.

Polymeric:

Carbon atoms can form with other atoms to make long chain molecules called polymers. If the polymers are arranged into a repeating pattern we can make crystalline polymers. Rubber is made up of polymers, when they are tangled together it is amorphous, when you stretch the rubber it becomes crystalline.