Carbon is found in many different compounds. It is in the food you eat, the clothes you wear, the cosmetics you use and the gasoline that fuels your car. In addition, carbon is a very special element because it plays a dominant role in the chemistry of life.
Carbon has four electrons in its valence shell (outershell). Since this energy shell can hold eight electrons, each carbon atom can share electrons with up to four different atoms. Carbon can combine with other elements as well as with itself. This allows carbon to form many different compounds of varying size and shape.
Carbon alone forms the familiar substances graphite and diamond. Both are made only of carbon atoms. Graphite is very soft and slippery. Diamond is the hardest substance known to man. If both are made only of carbon what gives them different properties? The answer lies in the way the carbon atoms form bonds with each other.
There are strong covalent bonds between carbon atoms in each layer. But, only weak forces exist between layers. This allows layers of carbon to slide overeach other in graphite.
On the other hand, in diamond each carbon atom is the same distance to each of its neighboring carbon atoms. In this rigid network atoms cannot move. This explains why diamonds are so hard and have such a high melting point.
The 3-D coordinates for graphite and diamond are available in the MathMol Structural Database. We urge you to download these structures to your home computer and use one of the suggested 3-D viewers.
The Molecule of the Month Page has recently included information on diamond located here
A third class of carbon compounds are called Amorphous Carbon
Image from: Amorphous carbon at low densities: An ab initio study
Amorphous carbon is free, reactive carbon that has no crystalline structure. Amorphous carbon materials may be stabilized by terminating dangling-π bonds with hydrogen. As with other amorphous solids, some short-range order can be observed. Charcoal and coal are examples of an amorphous carbon.
For a new way carbon can form see : What is the structure of the Carbyne molecule?
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