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.
 Click
on image for VRML 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.
 
Click on image for VRML 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.
 Click on the image for VRML
A java applet that shows the fullerene and allows rotation of the image
is now available here.
Compounds
made of Carbon
The simplest organic
compounds contain molecules composed of carbon and hydrogen. The compound methane
contains one carbon bonded to four hydrogens. Ethane is another example of a simple
hydrocarbon. Ethane contains two carbon atoms and six hydrogen atoms. In chemistry
we use a molecular formula to show how many atoms of each element are present
in a molecule. A molecular formula however does not show the structure of the
molecule. Scientists often use structural formulas to show the number and arrangement
of atoms in a compounds. Below the molecular formula for methane and ethane are
shown. Above the molecular formula are their respective structural formula. 
Although structural formulas can be very helpful they do not give a complete
picture of a molecule. Structural formulas do not tell us anything about the distances
between bonds, the angles formed by these bonds, or the size and shape of the
molecule. Scientists use three different representation to show what molecules
look like. THE WIRE FRAME MODEL 
This model clearly shows the type of atoms in the molecule, the distances between
bonds, and angles associated with the atoms. Because the lines drawn are very
thin, molecules can very easily be manipulated when viewed on a computer screen.
THE BALL-AND-STICK MODEL 
Atoms are represented by balls and bonds are represented as sticks.
THE
SPACE FILLED MODEL 
This model shows the space that the molecule will take up. Because of all
the points required to draw this molecule on a computer screen you should expect
these molecules to be very difficult to manipulate.
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