CARBON (C)

last update 01 oct 08

* Carbon is a member of the main-group nonmetals family:

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   CARBON / C / 6 

   There are three forms of pure carbon:  amorphous carbon (carbon
   black), graphite, and diamond.  Graphite consists of carbon atoms
   linked together in a hexagonal grid, forming a sheet; solid
   graphite consists of accumulations of such planes, and since they
   slide easily over each, graphite is soft.  Diamond results from
   graphite kept under long-term pressure; the bonds form an extremely
   strong three-dimensional lattice, and so diamond is one of the
   hardest substances known.

   Most (99%) of the carbon found in nature is C<12/6>, with the
   remainder mostly C<13/6>.  They are both stable, but traces of
   radioactive C<14/6>, with a half-life of 5,730 years, can also be
   found.

     atomic weight:       12.0107
     abundance:           15th
     density:             1.8 to 2.1 g/cc (amorphous carbon)
     density:             1.9 to 2.3 g/cc (graphite)
     density:             3.5 g/cc (diamond)
     melting point:       3,560 C (graphite); diamond burns at 800 C
     boiling point:       4,200 C (graphite)  
     valence:             2 3 <4>
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Graphite is used in pencil leads, as a lubricant, and for industrial electrodes. Diamond is of course used in jewelry, and also as an industrial abrasive. Synthetic diamond technology has advanced to the point where diamond may become a very common industrial or even commercial material -- diamond coatings for ever-sharp knives and razors, for example.

Some classes of gas or liquid filter systems use what is known as "activated carbon". Activated carbon for gas filter systems is obtained from coconut or other nut shells, ground up and "cooked" with steam or carbon dioxide at a temperature of about 100 degrees Celsius. The activated carbon granules are highly porous, giving them a large surface area to provide adsorption. Activated carbon for liquid filtration is similarly derived from wood, peat, or coal; this type of activated carbon has a larger pore structure.

There are also synthetic forms of pure carbon that consist of the hexagonal graphite plane wrapped into spheres or tubes, called "carbon nanospheres" and "carbon nanotubes" respectively; they are also known as "buckyballs" and "buckytubes" respectively, after the colorful American inventor R. Buckminster Fuller (1895:1983), who developed "geodetic" dome buildings with geometric structures like those of carbon nanospheres. They are effectively forms of soot particles and, after they were discovered in the lab, were found in nature as well. They are fabricated by vaporizing coal with an electric arc or laser and then feeding the carbon vapor to a catalytic process. The process will often produce nested carbon nanospheres and nanotubes.

Carbon is an absolutely essential component of life; it provides the basic structural element for nearly all biomolecules. Fossil fuels, such as coal and petroleum, are derived from carbon-based biomolecules, as are synthetic plastics of various forms. Carbon dioxide gas (CO2) is a trace element in the atmosphere, but a very important one, since it supports plant respiration, and global temperature is very sensitive to CO2 concentrations.