New Carbon Molecules
Buckminsterfullerene and Nanotubes Join Diamond and Graphite
The two forms of elemental Carbon - graphite and diamond - have been joined by further forms, the soccer ball-shaped Buckminsterfullerene and molecular-sized Nanotubes.
Carbon is one of the most important and abundant elements in the world. Along with Hydrogen, Oxygen, Nitrogen, it is the foundation of all organic compounds, the building blocks of living things. In its pure elemental form Carbon can exist in different forms. This is because of the way it bonds with itself.
Chemical Bonding
Every atom is made up of a positively charged nucleus, containing protons and neutrons, and shells of constantly moving, negatively-charged electrons. The numbers of electrons in the outer shell of each atom determines the way it will bond with other atoms. The outer shell of carbon contains four electrons, but it has space for eight, usually organised in four pairs. This means that a carbon atom can comfortably make four bonds by sharing a spare electron in the outer shell of another atom. A bond formed by a shared electron pair is called a “Covalent Bond”.
Diamonds
When a carbon atom bonds to another carbon atom, there are two structures possible. The most stable is a tetrahedral structure. This is like a triangular based pyramid with the carbon atom at the centre. Each bond is as far away from the other bonds as possible, making the structure stable and strong. This is the structure of diamond, one of the hardest materials on earth.
Graphite
The other possible structure involves each carbon atom bonding to three others in a planar structure of hexagons, each bond at an angle of 120° to the others. This leaves one unbonded electron per carbon atom. These “spare” electrons mix together to become a kind of “cloud” of electrons loosely holding the flat layers of strongly bonded carbon together. This is the structure of graphite and explains the way pencils write. As the pencil moves across the paper, the flat layers of carbon slide away from one another and stick to the paper. It also explains why graphite conducts electricity. A conductor needs to have mobile electrons, which there are between the graphite layers.
Third Form
For many years it was thought that these were the only two types of elemental carbon available. Then in the mid-1980s Dr Harry Kroto and other scientists began to publish results of their experiments to produce another form of elemental carbon. They were able to isolate a molecule of carbon with the formula C60 – a molecule made up of sixty carbon atoms. They went on to win a Nobel Prize for the discovery of this molecule which they found was in the structure of a soccer ball. The carbon atoms were bonded together in threes, like in graphite, but instead of just forming hexagons, some pentagons were included which made the molecule become a sphere, like in a geodesic dome. The balls were named Buckminster Fullerene after Richard Buckminster Fuller, an architect who used geodesic domes in his work.
Later Nanotubes were discovered. These are cylindrical molecules made up of carbon atoms. They are like the flat plates of graphite rolled up. They are very strong, good conductors of electricity and heat and chemically inert. They are not much more than one nanometre wide but have been made up to four centimetres in length. They have been made into a type of paper which, with the properties just outlined will become a very useful substance.
Applications
Since their discovery, much research has been done and potential uses of these new molecules have been suggested. These include reducing radiation side effects, treating cancer, making light-weight body armour and other engineering applications. They really seem to be almost “miracle molecules” and their importance can only increase.
