Carbon is a funny
element. It comes in different shapes and colors. Maybe the most common
are black powders (coke, graphite) but it can also show up as the crystal
clear, shiny and utterly hard diamond. That's right, diamonds are made
just of plain carbon atoms. But in diamonds those atoms are arranged in
a very special way, only attainable under very high pressures. In this
case these rare stones are scarce not because of what they are made
from but because of the unique conditions in which they are formed.
In any case,
graphite is a common material that you can find in pencils, pretty cheap.
Crystals of diamond are so scarce and difficult to find that we have been
convinced to pay the equivalent to many, many, many pencils to put one
in a ring for mating rituals.
In graphite
carbon atoms form layers where each atom is surrounded by three other identical
atoms. In diamond each carbon is bonded to four neighbors in a tetrahedral
arrangement.
The structure
of each of these two materials, the innermost arrangement of their atoms
is what determines their properties. The three-dimensional arrangement
in diamond provides much harder crystals than for graphite where the layers
can easily slide making it in fact a good solid lubricant.
All this has
been very well known for many years. But recently carbon has shaken the
world of materials by showing up in a new disguise. A new form of carbon
(indeed a whole new kind of forms) was discovered in 1985. A form consisting
of a spherical arrangement of sixty carbon atoms is the best known and
is shown in the following figure:
This C60 ball is also known as buckminsterfullerene or just fullerene in honor to the american engineer R. Buckminster Fuller who had designed a geodesic dome for EXPO'67 in Montreal making use of hexagons and some pentagons to curve the surface. Fullerene is indeed a remarkable arrangement of sixty identical, totally equivalent carbon atoms (blue balls above) each with three bonded neighbors as in graphite but with a peculiar topology of alternating hexagons and pentagons leading to a closed sphere.
This new form
of carbon can be isolated from the soot obtained by setting up an arc discharge
between two graphite electrodes. This is like a lab-made lightning experiment.
It's HOT CHEMISTRY leading to HOT MOLECULES!.
Other fullerenes
and other related materials have followed C60 in making headlines, among
them C70, onion-shaped structures and cylindrical nanotubes. The history
of fullerenes is a perfect example of an extraordinary new compound, the
fruit of excellent basic research, leading to a new field of chemistry
and to new materials that will certainly find many different applications
in all sorts of high-tech devices.
But what about
the funny shape? . Well...Buckminster Fuller cannot be said to be the only
human wisely combining hexagons and pentagons to form a sphere. Some anonymous
guy must have had the same idea because C60 is exactly identical
to a soccer ball !
Last modified: 9 Feb 1999
©Pedro Gómez-Romero,
1998, 1999
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