Discovery Of A Molecular Solid Carbon example essay topic

The Scientific Significance of Buckyballs by Chemistry Section General Chemistry Prof. Spring 199 Until the mid-1980's, elemental carbon was believed only to exhibit two main allotropic forms, diamond and graphite, both of which are covalent-network solids. However, Nobel Prize winning research conducted in the United States and Europe has confirmed the existence of a third previously unknown form of carbon- buckminsterfullerene (C 60). The discovery of buckminsterfullerene's, named after Richard Buckminster Fuller, an architect who explored similar shapes in "geodesic" domes made from glass and metal, or buckyballs as they are more commonly referred to, was made at Rice University, Texas in 1985, during experiments to investigate carbon clusters formed by laser ablation of graphite (Pool 1996). The discovery significance was clear from the beginning. "It is hard to identify any other recent finding in chemistry that has stimulated such intense and diverse activity throughout the physical sciences" (Ball 1996). It was clear that the discovery of C 60 and the related carbon-cage clusters, collectively known as fullerenes, "would change organic chemistry and materials science" (Ball 1996 p. 561).

The conceptual beginning of fullerene science was early as 1966, when David Jones (writing under the pseudonym Daedalus) speculated about a curved form of graphite similar to geodesic cages (Kroto 1993). However the study of fullerenes was not fully undertaken until the research conducted by Harold W. Kroto of the University of Sussex in Brighton, United Kingdom and Richard E Smalley and Robert F. Curl Jr. Of the Rice University in Houston. Prior to the discovery, researchers knew of only two naturally occurring forms of carbon: graphite, a soft, black slippery solid in which neighboring carbon atoms are arranged in parallel sheets of hexagon held together by London forces, and diamond: a clear hard solid in which neighboring carbons are grouped into pyramids forming a covalent network (Service 1996). Kroto who was studying the formation of long-chain carbon molecules, called cyanopolyynes, in interstellar space was interested in producing them in a lab. Smalley and Curl had developed a unique machine, that they were using to study semiconductor clusters, which vaporized small pieces of material using a laser and using a stream of helium gas swept the resulting plasma stream along a high-speed in which molecules and clusters of varying size would form.

Working together they began experimenting with graphite. After several days experimenting with and vaporizing graphite, the chemists had found the long chains of carbon atoms that Kroto was looking for. However they had also discovered something else (Pool 1996). Mass spectrometer readings of the vaporized carbon showed some particularly interesting data. The mass spectrum exhibited some peaks corresponding to clusters of carbon atoms with an atomic mass of 720 amu. This molecule consisting of 60 atoms exhibited properties of being extremely un reactive and unusually stable.

But how could this be "Sheets and pyramids of carbon are only stable when laced together in huge, continuous structures- a diamond for instance. When a carbon structure has as few as 60 atoms, the many dangling bonds at the edges of the sheet or pyramid make the structure highly reactive" (Service 1996). The only explanation for such a molecule would be the structure of the fullerene, a closed carbon-cage molecule containing only pentagonal and hexagonal rings (Fowler 1995). The fullerene hypothesis, as it was known, answered questions concerning the molecules thermodynamic stability. However, the famous soccer ball shape, technically known as a truncated icosahedron, was not fully accepted and many scientist were skeptical. But all doubts concerning the structure were laid to rest when in 1990 a team of physicists- led by Donald Huffman of the University of Arizona and Wolfgang Krtschmer of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany- succeeded in synthesizing measurable quantities of fullerenes thereby isolating and characterizing representatives of the fullerene family (Fowler 1995).

Huffman and Krtschmer found that an appreciable amount of buckyballs could be prepared by electrically evaporating graphite in an atmosphere of helium gas. Discovered in the soot were the C 60 molecules, confirming the structure, and a related molecule, C 70, for which an egg-shaped geometry was proposed (Kroto 1993). It was this follow up discovery to the research conducted by Kroto, Smalley and Curl that allowed fullerene science to blossom. The fact that buckyballs can superconduct, lubricate, and absorb light, promises many applications. Research has been able to alter the fullerene cages.

They have filled them with other atoms, chemically modified their surfaces, and elongated them in to tubes and rods (Wu 1996). Super conduction is one of the astonishing applications of the fullerene. Films of solid C 60 have been doped with alkali metals are able to superconduct at up to 33 degrees Kelvin, 20 K above the previous record for a molecular superconductor (Ball 1996). They have also used buckyballs as cages to enclose atoms.

Researchers have discovered ways to both insert atoms into cages and tack them onto the outside in an effort to make new materials with unique electrical, optical, and magnetic properties (Service 1996). They have also learned to modify the buckyball production process to create swollen spheres with many more than 60 carbon atoms. Another advance made, using what they have learned about fullerenes, was the creation of "bucky-tubes"- long cylinders that could be used in superstrong composite materials (Pool 1996). These carbon nanotubes are the most celebrated examples of newly discovered carbon based materials (Ball 1996).

The tube shaped fullerenes are promising in that they can be applied for possible uses in everything from tips for scanning probe microscopes to arrays of mini-electron guns for flat panel displays (Service 1996 p. 346). The discovery of a molecular solid carbon is truly remarkable. Fullerene science has led to the beginning of a new view of materials science at the interface of the molecular and bulk scales (Ball 1996). Properties of fullerenes are very different from those of any molecules known to date leaving an air of excitement surrounding its discovery. Bucky balls are scientifically significant because the chemistry of the newly discovered molecule, will lead to the development of some very new chemistry of carbon in the years to come.

Bibliography

Ball, P. Fullerenes finally score as Nobel committee honours chemists. Nature 17 October: 561; 1996.
Fowler, P.W. ; Manolopoulos, D.E. An Atlas of Fullerenes. Oxford: Clarendon Press; 1995.
Kroto, H.W. ; Fischer J.E. ; Cox, D.E. The Fullerenes. Oxford: Pergamon Press; 1993.
Pool, R. Buckyball pioneers score the ultimate goal. New Scientist 19 October: 6; 1996.
Service, R.F. A Captivating Carbon Form. Science 18 October: 345-346; 1996 Wu, C.
Buckyballs bounce into Nobel History. Science News 19 October: 247; 1996.