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. The
element carbonCarbon
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.
Notice that graphite is
layered.
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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.
 
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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 has recently been discovered. They are called fullerenes.
The figure shown on the left is one form composed of 60 carbons. Notice the geometric
patterns of pentagons and hexagons that form the familiar icosohedron.
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