Hot Molecules

    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 !

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©Pedro Gómez-Romero, 1998,1999
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