What is the link between diamond, graphite and buckyballs?

They are all composed only of carbon. What determines the properties of any substance? Simple. The properties of any substance depend on the type and number of atoms they are composed of, and of course on how those atoms are joined together. Water and hydrogen peroxide, for example, are both composed only of hydrogen and oxygen, but a molecule of hydrogen peroxide has two hydrogen atoms and two oxygen atoms while water of course has two hydrogens and one oxygen. So even though they have the same components, they have dramatically different properties. Two substances may even contain exactly the same types and numbers of atoms, but still be totally different because of the way the atoms are joined together. A classic example is ammonium cyanate and urea, both of which correspond to the formula N2H4CO but are very different. Urea is a breakdown product of proteins and shows up in the urine while ammonium cyanate is a mineral substance. These two hold a fundamental place in chemical history because of a classic experiment carried out by Friedrich Wohler in 1828. Wohler heated ammonium cyanate and converted in to urea. At the time it was believed that substances found in living systems, such as urea, were held together by some sort of “vital force” that could never be reproduced in the laboratory. Wohler’s experiment disproved this and spawned the modern field of organic chemistry. Before Wohler organic chemistry was described as the chemistry of substances found in living or once living systems and were believed to be beyond the scope of laboratory synthesis since they could not be infused with the necessary vital force. Wohler, however, had shown that organic molecules were not characterized by any mysterious force, their common feature was that they all contained carbon atoms. And these carbon atoms readily joined to each other as well as to other atoms in a myriad ways giving rise to a vast array of organic compounds ranging from fats and proteins to the flavour of vanilla and the odour of a rose. Diamond, graphite and buckyballs are examples of the variety of ways carbon atoms can join together, and are particularly interesting because they contain only carbon atoms. In diamond the atoms are arranged in a three dimensional lattice, while in graphite they are joined together in an array of planar six membered rings, arranged in layers. The diamond is very hard while the possible movement of the layers in graphite makes it into an excellent lubricant. “Buckyball” is a colloquial term for a molecule in which sixty carbon atoms are joined in a sphere, as if located at the corners of the panels used to make a soccer ball. The curious name comes from the geodesic dome concept pioneered by architect Buckminster Fuller. In 1996, Harold Kroto, Richard Smalley and Robert Curl received the Nobel Prize in chemistry for their synthesis of fullerenes, of which buckyball is an example. Despite the fact that they are composed of the same atoms, diamond, graphite and buckyballs have completely different properties. Such is the magic of molecular bonding.

Joe Schwarcz

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