C4g Nanochemistry


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C4g Nanochemistry

  1. 1. C4g Nanochemistry Allotropes of Carbon • Allotropes are different structural forms of the same _________________. • Carbon can arrange it’s electrons in different ways to form these allotropes: 1. Diamond 2. Graphite 3. Nanoparticles – e.g. ___________________ and _________. Diamond • Diamonds are _______ and ____________________ and ____________________ (they sparkle). • Each carbon atom has ___ strong covalent bonds to __ other carbon atoms. They make the structure very _________________. • Diamond is the ________________ natural substance due to the 4 strong covalent bonds. • 4 strong covalent bonds from every carbon atom also mean that the melting point is very _________ because the bonds would have to be ______________ and this takes a lot of energy. • Diamonds are ____________________ in water. • Diamonds do NOT conduct electricity (they have no free e-) Uses: 1. Diamond is used to make cutting tools because 2. Diamonds are used to make jewellery because
  2. 2. Graphite • Graphite is ____________ and _____________ but also quite ____________ (shiny). • Each carbon atom forms just ____ strong covalent bonds. • Graphite forms sheets (layers) of carbon atoms. 1 sheet 3 layers of carbon sheets • The unbonded electrons sit between the layers and loosely hold them together with _____________ forces. • This means the layers are very ___________ to separate and they __________ over each other making it ________________________. Use 1: • Graphite is insoluble in water • The 3 covalent bonds take a lot of energy to break so graphite has a __________ melting point. • Graphite can conduct electricity because the electrons between the layers are _________________________________. Use 2: THERE IS A SEPARATE SHEET FOR QUICK REVISION OF SOME OF THE ELECTROLYSIS THAT WE HAVE COVERED SO FAR.
  3. 3. General revision of some electrolysis involving graphite (carbon) electrodes 1. General electrolysis cell 2. Electrolysis of Al2O3 3. Electrolysis of molten NaCl
  4. 4. Summary to compare Diamond and Graphite Diamond Graphite • 4 strong ___________ bonds from • __ strong covalent bonds from each each carbon to 4 other carbon atoms carbon to __ other carbon atoms • no free ______________ to conduct • sheets of carbon atoms in layers held electricity loosely together by ________ forces • __________free to move and conduct 1. 1. 2. 2. 3. 3. 4. 4. 5. 5. 6. 6. 7. 7. Uses: cutting tools Uses: dry lubricant jewellery pencils electrodes
  5. 5. Buckminsterfullerenes and Nanotubes Also known as a Bucky Ball • black solid • deep red in solution in petrol • Buckminster fullerene has the formula C60 i.e. it is made from 60 carbon atoms HIGHER The uses of fullerenes • It is thought that fullerenes could be used to ‘cage’ other molecules. These ‘caged molecules’ could then be used as drug delivery systems. • The advantage is that they could be made to target specific areas of the body where a drug is most needed. This is particularly useful if you have a drug that may be toxic to other parts of the body e.g. in chemotherapy to cure cancerous cells. • Alternatively they could be used to provide a slow release system for a drug Nanotubes Fullerenes can be joined together to make nanotubes Properties of Nanotubes: 1. very strong 2. electrical conductors
  6. 6. Uses of Nanotubes: 1. ________________________ in electrical circuits 2. _________________________ – nanotubes have a huge surface area on which to attach the catalyst molecules. Increasing the surface area of the catalyst means it is more efficient and this means more money can be made in the same amount of time 3. To ______________________ graphite in tennis rackets Chemistry versus Nanochemistry Example yotta 1024 1000 000 000 000 000 000 000 yottametre zeta 1021 1000 000 000 000 000 000 000 zetametre exa 1018 1000 000 000 000 000 000 exametre peta 1015 1000 000 000 000 000 petametre tera 1012 1000 000 000 000 terametre giga 109 1000 000 000 gigametre mega 106 1000 000 megametre kilo 103 1000 kilometre 100 1 metre milli 10−3 0.001 millimetre micro 10−6 0.000 001 micrometre nano 10−9 0.000 000 001 nanometre pico 10−12 0.000 000 000 001 picometre femto 10−15 0.000 000 000 000 001 femtometre atto 10−18 0.000 000 000 000 000 001 attometre zepto 10−21 0.000 000 000 000 000 000 001 zeptometre yotto 10−24 0.000 000 000 000 000 000 000 001 yottometre • Chemistry works with materials on a ________________ scale e.g. grams, kilograms, tonnes, megatonnes • Nanochemistry works with materials on an ______________ scale e.g. nanometres Why is this important? Nanoparticles have different properties to the ‘bulk’ chemical. e.g
  7. 7. Higher What is Molecular Manufacturing? (also known as molecular engineering) Molecular engineering creates nanoparticles to a specific design. This can occur in one of two ways: 1. 2.
  8. 8. The discovery of buckminsterfullerene Topics Allotropy, organic chemistry, chemists In 1985, virtually all school chemistry textbooks became out of date overnight. Prior to this, textbooks stated that there were two allotropes of carbon – diamond and graphite. Allotropes are forms of the same element which differ in the way their atoms are arranged. Diamond and graphite are classic examples of allotropy. In diamond the carbon atoms are arranged tetrahedrally and in graphite they form two-dimensional layers of interlinked hexagons. Picture Diamond and graphite structures In 1985 the discovery was announced of a third allotrope in which the atoms form C60 molecules in the shape of a football. This led to the award of the 1996 Nobel Prize to Harry (now Sir Harry) Kroto of Sussex University, Robert Curl and Richard Smalley (both of Rice University in Houston, USA). Harry Kroto had an interest in molecules found in interstellar space which can be identified from their microwave spectra – by comparing signals obtained from outer space with those measured for known compounds in the laboratory. He was particularly interested in poly-ynes (molecules with several carbon-carbon triple bonds) but these are difficult to make conventionally. In 1984, Kroto began collaboration with Smalley and Curl in Houston who had an apparatus called AP2 (‘App-two’). This used a laser to blast clusters of atoms off solid targets and then led the clusters into a mass spectrometer where their relative molecular masses could be measured. Kroto hoped that if a graphite target were used, small sections of graphite layers might rearrange themselves into poly-ynes whose spectra could then be measured. Clusters of carbon atoms were indeed formed, and unexpectedly large peaks were found in the mass spectra with masses corresponding to C60 and (at a lesser intensity) C70. These peaks always appeared together, and Kroto started to refer to them as the Lone Ranger and Tonto. Why were these molecules so stable? Sheets of graphite in which the carbon atoms are arranged in hexagons would be expected to be very unstable because they would have so many ‘dangling bonds’ with unpaired electron at the edges. Inspired by geodesic dome structures made up of hexagons designed by the architect Richard Buckminster Fuller, the team began to consider the possibility that a sheet of graphite hexagons might curl up into a spherical shape so that all the ‘dangling bonds’ could link up. However, work with crude paper molecular models showed that this was impossible if all the atoms were linked in hexagons. Kroto recalled a spherical ‘stardome’ made of cardboard shapes that he had built for his children and believed that it contained pentagons. This was a vital clue. More late night work with the paper models showed that a spherical shape could be made with 20 hexagons and 12 pentagons. A quick counting of bonds showed that this structure was chemically reasonable in that each carbon atom was forming four covalent bonds – one double and two single. Having made the model, the team did not know what the geometrical shape was and the story goes that a phone call to the chairman of the Rice University Mathematics Department for advice elicited the reply ‘what you’ve go there boys is a soccer ball’. However, Kroto remembers a less laconic reply. ‘We were sitting in Rick Smalley's office. We were extremely high, on a roll at the time as you might imagine, only just recovering from the realisation of what the bloody thing might be. Jim Heath [a student of Smalley’s] and I and almost certainly Sean O'Brien [another student of Smalley’s] and probably Bob Curl too were there. Rick was definitely not there at the
  9. 9. time and that is why Jim was sitting in Rick's chair at Rick's desk when the phone rang. Jim answered it. Then a sort of stunned expression came over his face and Jim said ‘It's soccerball’, or he may have said ‘He says it's soccerball’. I am pretty sure he did not say ‘It's a soccerball’. This appeared to be a return call from a mathematician that Rick must have called up earlier in the day to ask what the structure might be.’ Picture The ‘soccerball’ structure of buckminsterfullerene At this stage, the soccer ball structure (and a similar ‘rugby ball structure for C70) was no more than inspired speculation. Confirmation had to wait until enough C60, now christened buckminsterfullerene (buckminsterfuller after the architect and ene because it had double bonds), could be made to allow, ultraviolet / visible, infrared and 13C NMR spectra to be measured as well as X-ray diffraction studies. App-two produced only minute amounts of molecules at a time. Theorists predicted that a ‘soccer ball structure’ should have just four lines in its IR spectrum (at specific wavelengths) and that its 13C NMR spectrum should have just one line because all the carbon atoms are in exactly equivalent positions. NMR is one of the most important techniques for organic chemists. The saying goes that ‘when the NMR breaks down, the chemists go home.’ To produce enough buckminsterfullerene for these tests, a different approach was used. Two graphite rods inside a bell jar containing an inert gas at low pressure were connected to an electrical supply, and an electrical arc formed between the two electrodes (one experimenter described this apparatus as ‘a battery and a pencil’).This produced a soot which was found to contain about 1% of a mixture of C60 and C70. These could be separated from the soot by sublimation or by extraction into benzene (in which the soot was insoluble) and from each other by chromatography. At Sussex Kroto and his student Jonathan Hare (now the presenter of TV programmes, Rough Science and Hollywood Science) together with Roger Taylor and Abdul Sada were the first to measure the single line 13C NMR spectrum (Kroto called it ‘the one line proof’). Wolfgang Krätschmer and Donald Huffman, working at the Max Planck Institute for Nuclear Physics in Germany and in Arizona State University, extracted the molecule and measured its X-ray pattern just ahead of the Sussex team and measured the IR and UV / visible spectra. Both events occurred in 1990. Krätschmer and Huffman had in fact observed the UV / visible spectrum some years earlier but without realising its significance. Further information This is a much simplified account both in detail of the actual experiments and the number of people, and indeed research teams, working on buckminsterfullerene. There is a much more detailed but highly readable account in J Baggott, Perfect Symmetry, Oxford: Oxford University Press, 1994. This was written before the award of the Nobel Prize, of course. As well as the story of the discovery, it deals with some of the chemistry and properties of the family of fullerenes and their derivatives. The Nobel lectures of the three laureates are available at www.nobel.se. Postscript Rick Smalley died in November 2005 after a long fight against leukaemia.