Themes > Science > Physics > Solid State Physics > Atomic Bonding and Crystal Structure > Crystal Structure and Crystal Planes > The Structure of Crystals

The beauty and symmetry of crystals have fascinated people for thousands of years. Somehow, they seem different from more ordinary matter. However, most solid objects are made of many tiny interlocking crystals. It is only occasionally that the individual crystals are large enough to catch our attention, as in these beautiful examples.

    










Celestite                                 Sulfur                                            Pyrite
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The atoms in a crystal are in a regular repeating pattern called the crystalline lattice.  Although the existence of this lattice has been known for many years, recently the scanning tunneling microscope (STM) was invented. This allows us to see individual atoms. Below is an STM image of a  platinum surface. Note the regular rows of Pt atoms.
 
This image is the property of IBM Corporation.

The lattice can have a profound influence on the material's properties. For example, below we see two crystals - graphite and diamond. They each contain only 1 kind of atom - carbon. The difference is in how those atoms are arranged.
 
 
Graphite                Diamond
 
The above images are the property of Amethyst Galleries, Inc., and may not be copied for commercial purposes.
Permission to copy descriptions and images is granted for personal and educational use only.
Refer to http://mineral.galleries.com/
 
Graphite is black, soft, and an excellent lubricant. This suggests that it must be easy to separate atoms in graphite, or at least to make them slide past one another.

Diamond is transparent, strong, and very hard. It is a superb cutting tool. The atoms in diamond must be very strongly held in position.

Chemically, diamond is inert. Graphite, on the other hand, is very useful for absorbing and catalyzing reactions.  The structures of diamond and graphite explain these differences.

The carbon atoms in diamond are each bound to 4 others in a 3-dimensional network. To change the shape of a diamond or break it requires that many of these strong bonds be broken simutaneously. Since there is little room for other molecules to get into the structure, diamond is not very reactive.


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