allotropes+of+carbon teacher+packet july+2007

7/30/2019 Allotropes+of+Carbon Teacher+Packet July+2007

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National Center for Learning and Teaching in Nanoscale Science and Engineering

2006 Professional Development Workshop Purdue University 1

Allotropes of Carbon

Teacher PacketAuthor: Dave Sederberg ([email protected]) Content Area: ChemistryDraft Date: May, 2007 Grade Level: 9-12

LESSON RATIONALEWhen an element can exist in more than one form, either as a result of differences inmolecular composition or from different packing arrangements of atoms in the solid state,these forms are called allotropes. Allotropes often have vastly different physical andchemical properties, even though they are composed of identical atoms of the sameelement.

The characteristic properties exhibited by the allotropes of carbon are a result of thestructural arrangement of the atoms and the forces that bind them together. This activityis intended to help students understand the relationship between the atomic structure of amaterial and the characteristic properties that the material exhibits. This relationship ismost pronounced at the nanoscale, where the proportionality between dimensions, likesurface area to volume, is extreme and the difference in properties resulting fromstructure are profound.

This lesson, accompanied by the video Race to Catch a Buckyball will provide studentsthe opportunity to delve into the relevance of scientific research and the role of serendipitous discovery in the building of scientific knowledge.

Big Ideas of Nanotechnology Related to this Lesson

ModelingModeling is a critical tool for scientists, combining evidence with creativity,helping to organize observations with data for the visualization of objects andphenomena and prediction for future testing. Creating a model of thebuckyball made it possible for scientists to predict properties of the moleculeprior to actually obtaining it in the laboratory.

Size and ScaleBuckyballs and Nanotubes, with dimensions in the 1 to 10 nm range exhibitthe high proportionality between surface area to volume indicative of particlesand structures in the nanoscale.

Particulate Nature of Matter All carbon allotropes are composed of identical atoms and those atoms are inconstant and random motion. Yet, the physical arrangement of the atoms inthese structures, and the modes by which they are bonded together, are


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responsible for some unique and unusual properties, such as hardness, tensilestrength, conductivity, flexibility and reactivity.

Technology and SocietyWhile nanoscale structures such as buckyballs and nanotubes offer greatpotential for commercial application in current, as well as yet unpredictedaspects of science, there is no consensus as to the risk of their beingincorporated into living organisms, the food chain or the environment.Additional ethical, cultural and societal issues may need to be resolved aswell, with more controversial applications.

Instructional Objectives Explain what allotropes are and name the four allotropes of carbon. Describe characteristics among a family of allotropes that are the same to all

members of the family and those that are different. Construct molecular models for allotropes of carbon. Relate the way in which the carbon atoms are bonded together to the differences

in allotropic properties. Explain the role of the model in scientific research. Explain how two scientists can make different interpretations and reach different

conclusions from the same data and experimental evidence. Illustrate the tentative nature of scientific knowledge, using evidence from

research to obtain and characterize the buckyball. Recognize potential social and ethical implications that can arise when newly

discovered and developed materials become available prior to full knowledge of potential safety issues and consequences of use.

Standards

Indiana State StandardsGrades 9-12

C.1.26 Describe physical changes and properties of matter throughsketches and descriptions of the involved materials.

C.1.28 Explain that chemical bonds between atoms in molecules, such asH2, CH 4, NH 3, C 2H4, N 2, Cl 2, and many large biological moleculesare covalent.

C.1.35 Infer and explain physical properties of substances, such as meltingpoints, boiling points and solubility, based on the strength of molecular attractions.


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C.1.36 Describe the nature of ionic, covalent, and hydrogen bonds andgive examples of how they contribute to the formation of varioustypes of compounds.

National StandardsGrades 9-12

Content Standard A: Science as Inquiry

Identify questions and concepts that guide scientific investigations.

Formulate and revise scientific explanations and models using logicand evidence.

Use technology and mathematics to improve investigations andcommunications.

Standard G: History and Nature of Science

Science as a human endeavor.Nature of science.

LESSON PREPARATION

Materials (per class of 24 students, working in pairs)

Item Number/Amount

Commercial model kit(s) (graphite, diamond, buckyball)(1)

1 of eachPaper model buckyball templates 24 (1 per student)

Nanotube transparencies (hexagonal graph paper) (2) 36 (3 per group)

Glue pen (3) 12 (1 per group)

Scissors 24 (1 per student)

Cellophane tape 2 rolls

Sample of graphite rock (4) (optional) 1

Computers with internet access 12 or 24(1)Vendors for commercial models include Flinn Scientific (www.flinnsci.com) and

Science Kit Boreal Laboratories (www.sciencekit.com).(2)These can be re-used with each class.(3)The Avery brand Glue Pen works well (#65781, Avery Permanent Bond

Disappearing Color Glue Pen).(4)Science Kit Boreal Laboratories (www.sciencekit.com)


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Anticipated Time Allotment

2 -3 hours including introduction and discussion.

Lesson segment: minutesLeading questions and discussion 15

Predictions from models; brainstorm properties of allotropes 15

Search World Wide Web for data and properties of the allotropes 20

Discussion of search results and status of knowledge 5

Build models and answer study guide questions 30

Watch the video, Race to Catch a Buckyball 50

Discussion 20

Assessment 10

Pre-Class Preparation

Background (provided in student packet)

Carbon in a nutshellThe element carbon is the backbone of life on our planet. Carbon, like most otherelements heavier than helium, was synthesized in the stars. It has been cycled andrecycled from earthen minerals into the air, through animals and plants and back to theearth countless times. Carbon has been a familiar and useful material since prehistory, in

the form of charcoal and soot, although it was not until late in the eighteenth century thatcarbon actually came to be recognized as an element (Greenwood & Earnshaw, 1984).

The name carbon was actually coined by Antoine Lavoisier (Fr. carbone) from the Latincarbo meaning charcoal. Swedish chemist Carl Wihelm Scheele, in 1779, showedgraphite, a familiar sooty material, to consist of pure carbon (IN-VSEE, 2006). Thatdiamond was composed only of carbon as well was demonstrated just a few years later byboth Antoine Lavoisier and Humphry Davy, each of whom performed the costlyexperiment of burning diamond in excess oxygen, identifying as the only product, carbondioxide. Thus, by the end of the 1700s, diamond and graphite were proven to becomposed of atoms of the same element carbon, except that they existed in physicallydifferent forms (Zaugg, 1990).

The word diamond comes from a blend of the ancient Greek words diaphanes ,transparent and adamas , invincible, referring to its extreme hardness (Greenwood &Earnshaw). The name graphite, proposed in 1789 from the Greek, graphein , to write,illustrates one of the uses for this form of carbon (Greenwood & Earnshaw, 1984).

Diamond is the standard for hardness against which the hardness of other materials ismeasured. Pure diamond is colorless and transparent. It has the highest melting point of any known substance, is the hardest of any naturally occurring solid and it was the firstmaterial to have its crystalline structure determined by x-ray diffraction (Gale, 2005).


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Each carbon atom in diamond is covalently bonded to four neighboring atoms forming arigid three dimensional tetrahedral network.

In contrast to diamond, graphite is blackish, waxy, soft and slippery feeling, but is more

thermodynamically stable than diamond. Graphite is composed of carbon atoms, eachbonded to three other carbon atoms, arranged in a repeating hexagonal pattern in flat twodimensional sheets. These sheets, held together by only weak attractive forces, stack together to make the solid crystal. These two materials, diamond and graphite, vastlydiffer in both their appearance and in their properties, yet, despite their obviousdifferences, both are pure carbon; both are composed of identical atoms..

AllotropyLike carbon, a number of elements (for example, B, P, Sn, Pb and S), exist in differentforms, different physical arrangements of the atoms, each possible arrangementexhibiting contrasting and unique properties. When an element can exist in more than one

form, either as a result of differences in molecular composition or from different packingarrangements of atoms in the solid state, these forms are called allotropes . Allotropesoften have vastly different physical and chemical properties, even though they arecomposed of atoms of the same element.

In the two hundred years following the work of Lavoisier and Davy, the number of allotropic forms in which carbon was known to exist was only two - diamond andgraphite. Events in 1985, however, brought a paradigm shift to the field of carbonchemistry with an epic history-making discovery. Two graduate students, working in thelaboratory of Richard Smalley at Rice University, discovered the formation of an entirelynew form of carbon, in fact a whole family of stable carbon molecules, the most abundantspecies of which was a molecule of sixty atoms, C 60. A slightly larger molecule C 70, also

appeared as a stable species in the mix. The carbon atoms in these molecules hadassembled from carbon vapor into solid molecular units stable molecules with aspecific number of carbon atoms, resistant to further growth or modification, (Kroto,Heath, OBrien, Curl, and Smalley, 1985).

The research team at Rice worked tenaciously with paper models, jelly beans andtoothpicks, geometric solids, and creativity, fitting experimental evidence with the knownchemical behavior of carbon, attempting to figure out how the atoms in these moleculeswere connected together. Ultimately, the only structure which could offer a reasonableexplanation for this behavior, and still provide each carbon atom with its correctcompliment of electrons, was a spherical one. These spherical structures were shown tobe composed of a repeating geometric arrangement of pentagon and hexagon carbonrings, resembling a geodesic dome. The surprising anomaly of these structures, however,compared to the previously known carbon allotropes, was that they contained a specificnumber of carbon atoms they were molecular carbon. These new carbon moleculesappeared to form from the carbon vapor surrounding them, programmed to somepredetermined size and exact number of atoms. Richard Smalley, Robert Curl, andHarold Kroto were awarded the Nobel Prize for their work in 1996.

Paying homage to Richard Buckminster Fuller, an architect famous for his work designing geodesic architectural domes, Smalley and Kroto named this family of


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molecules Buckminsterfullerenes . They are more commonly referred to as fullerenes,or, more affectionately, just " buckyballs ." With this discovery, a new and revolutionarythird allotrope of carbon had now been added to the two (graphite and diamond) already

known. Although initially found as laboratory anomalies, fullerenes have since beenshown to occur in nature, on the earth as well as in space. While a number of varieties of buckyballs have now been shown to exist, C 60 and C 70 are generally the most abundantand readily isolated fullerenes (Kroto et al., 1985).

In 1991 another variety of fullerenes were discovered, with properties similar to thebuckyball, but in a tubular, rather than spherical shape. The diameters of thesebuckytubes fall in the 1 to 10 nanometer range and as such were referred to asnanotubes , or carbon nanotubes (CNTs). Although the mechanism of their formation hasnot been fully determined, CNTs can be thought of as a "rolled up" a section of a graphitesheet, the ends capped with half a C 60, or other molecular fragment. The carbon polygonscomprising these structures can combine to create an almost infinite range of helical,

toroidal, and corkscrew-shaped tubes, all with different mechanical strengths andphysical properties (Gale, 2005).

The story of carbon, however, was destined to be re-written again. In 1993 Sumio Iijimaworking at the NEC Corporation in Japan discovered that carbon nanotubes couldactually be grown from vaporized carbon in the laboratory. The sizes of these structuresand the ways in which the atoms in them are arranged is controlled by the laboratoryconditions under which they are grown. These nanometer-scale structures have becomethe focus of enormous interest since they represent potential building blocks fornanostructured materials, composites, and novel electronic devices of greatly reducedsize.

The wide range extent of potential application of materials utilizing carbon nanotubes andbuckyballs can only be left to speculation. The revolutionary mechanical and chemicalproperties of these forms of carbon place them at the forefront of research, withanticipated applications ranging from the structure of aircraft to molecular electronics androbot molecules.

Getting the Materials Ready Students will need the paper templates for the models that will be used. The

NASA paper model is printed on a single sheet, either 8 x 11 or 8 x 14; bothsizes are provided. Each student should make their own model. The copies can bemade on regular copy paper, but a more durable model can be constructed using

60# or 70# card stock. Using different colors increases student interest. In order to compare the structure among the three configurations of the carbon

nanotube, each team will need to be provided three identical overheadtransparency templates. Unless it is the intent to provide students take-homemodels, the cellophane tape can be removed and the transparencies re-used forother classes.


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Variations/SuggestionsStudents are expected to have knowledge of the basics of chemical bonding and theperiodic table. An overview of hybridization would also be helpful, where appropriate to

the level or ability of the student and direction of instruction.The first part of the activity requires students to search the internet sleuthing forproperties of the four carbon allotropes. If students need some guidance as to where tolook, the following list may help, but any general search engine should be sufficient.

1. Properties of Diamonds http://newton.ex.ac.uk/research/qsystems/people/sque/diamond/

2. Diamonds http://ist-socrates.berkeley.edu/~eps2/wisc/Lect6.html

3. Graphite Properties Page by John A. Jaszczak http://www.phy.mtu.edu/~jaszczak/graphprop.html

4. The World of Carbon http://invsee.asu.edu/nmodules/Carbonmod5. Properties of Carbon and C60 http://www.creativescience.org.uk/propc60.html

6. Fullerene, C60 -http://www.chemicalland21.com/arokorhi/industrialchem/organic/FULLERENE%20C60.htm

7. Physical Properties of Carbon Nanotubes http://www.pa.msu.edu/cmp/csc/ntproperties/

Follow the time line above. If the element of time is an issue, the internet search of the

properties of the allotropes could be done by students outside of class, at home, before orafter school in the school media center, or during study hall or resource time. Equally, asan alternative, the paper models can be constructed by students at home as well. Whilestudents are building their models the teacher should circulate among the lab groups as aresource, to answer questions and to elicit student understanding .

You may elect to have students count the vertices and the number of hexagons andpentagons after they finish the paper buckyball models. As an alternative, prior to cuttingout the patterns, they can identify the positions of the atoms beforehand by drawing a dotwith a marker at each vertex. Then, when the buckyball is assembled, the dots will clearlyshow the geometric arrangement of atoms in the structure.

If bonding is an appropriate topic for the class, students can draw a line along the creasebetween all pairs of hexagons after the model is completed. These lines represent thedouble bonds shared by adjacent carbon atoms. Do not draw along the lines that createthe pentagons. Each hexagon should end up with single bonds and double bondsalternating around its perimeter, for a total of three single and three double bonds.

Once students have completed their models and answered the report questions, move onto the NOVA video, Race to Catch a Buckyball. Depending on the grade level andability of the students, it may be insightful to talk about bonding and hybridization,


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although these are not necessary to understand the development of the model portrayed.Additionally, images of mass spectra and UV spectra will be illustrated. Showingstudents examples of these in advance may be beneficial to their understanding the

reference during the video. These spectra are provided in the literature, referenced below(Kratschmer, Lamb, Fostiropolos & Huffman, 1990). In fact this is the paper actuallyreferred to in the video. Having several copies of the paper for students to see in advancewill enable them to actually see a real history-making journal research paper!

A main challenge faced by the scientists in the video is to determine the structure of atype of carbon molecule that had never been known previously. To provide studentsinsight, you may want to have them try, or demonstrate, some simple tessellationactivities. Tessellations are shapes which, when fitted together, will cover a flat surfacewith no gaps. Squares and rectangles are particularly easy to tessellate; pentagons, one of the shapes confronting buckyball researchers will not tessellate. Tessellations can befound in the pattern of tiles that cover bathroom walls and the brickwork patterns in

building walls and pathways. One of the challenges facing researchers in the elucidationof the structure of the buckyball was finding a geometric arrangement around whichatoms would fit within the normal parameters of their bonding patterns and angles(NOVA, 1995).

SafetyScissors might be the only safety concern for this activity.

DOING THE LESSON

Leading Questions/Pre-Lab DiscussionIntroduce the lesson with how materials of the same chemical composition can havedifferent properties. For example, high density versus low density polyethylene has thesame chemical composition, yet different physical properties. Similarly, diamond andgraphite are both pure carbon, yet each is distinctly dissimilar to the other. Each of morecommon allotropes of carbon, diamond and graphite, have had applications based on theirrespective unique properties for a long time. While buckyballs and nanotubes have beenon the scene only more recently, the potential for their use as structural materials or in themedical field are on the horizon.

Another aspect of this lesson pertains in several ways to the nature of science. In the

video that follows the lesson, Race to Catch a Buckyball, students will see the tentativenature of scientific knowledge, demonstrated by the fact that, while all scientists agreedprior to 1985 on the existence of two structured allotropic form of carbon, they were infact incorrect. The video also illustrates the way in which ones own theory or priorperception has an influence on the interpretation of experimental evidence and may infact obscure evidence or bias results.

Lastly, you might want to discuss the role that models play in science; how they are used,why they are used, what their benefits are, as well as their limitations. The use of models


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played a key role in the elucidation of the structure of the buckyball. Scientists haveevidence that the molecule existed, but it was only through the use of models that theygained insight on where to look for further data.

One of the methods by which a substance can be identified is by it absorption spectrum.The Race to Catch a Buckyball documentary illustrates how, through the use of UVspectroscopy, researchers attempted to confirm that the carbon compound that they madein the laboratory was indeed the same as that which they thought to occur in the stars.

The following Leading Questions can serve to set the foundation for this lesson: How is it possible that the element carbon can be used for decorative jewelry, as

a lubricant for moving parts, for the tips of long-lasting drill bits and to make arope strong enough to reach from the Earths surface to a satellite in orbit?

In the field of science, where does our knowledge come from? Once scientistsagree on what they know, is it possible that what they know will change?

If you thought you had made a new kind of molecule, but it was impossible tosee, what kinds of evidence would you look for to try to figure out exactly what it is?

Activity

Once the leading questions have been discussed, break students into groups of two orthree and provide each group with commercial models of diamond graphite andbuckyball. If sufficient model kits are available, several buckyball kits can be combinedto make a nanotube, but this can be optional. Based on appearance and manipulation of the models have students suggest evidence to support their predictions as to how the

physical and chemical properties of the allotropes might compare. Consider options suchas strength, hardness and chemical reactivity.

From the discussion of the physical models, move into a whole-class discussion aboutwhat kinds of properties are useful, in general, for the identification and characterizationof materials. Have two students come to the board to tabulate the class suggestions.Suggested properties can be debated as a class, assisted by teacher input, as to how usefulthey might be and perhaps put into columns based on perceived utility or type of property. The goal is to identify properties that students think might be useful indistinguishing one carbon allotrope form another. Encourage students to be creative andto see how many useful properties they can derive. Eight to ten should be a good guide.

Discuss suggested properties and illustrate why some of the students choices might bemore useful than others and difficulties that might be encountered.

Once there has been sufficient discussion for students to have an understanding of theirobjective, provide them with the prepared table, listing identifiable properties from theStudent Study Guide. Using the internet or other reliable research sources, students willsearch the properties for each of the four allotropes. As an alternative, the teacher cansimply provide students with a prepared table, complete with the properties of theallotropes already entered. In either case, briefly compare the known properties, where


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applicable, with students predictions based on their previous examination of thecommercial models.

Once the model-building portion of the lesson is complete, show the NOVA

documentary, Race to Catch a Buckyball. The video should need little introduction.One suggestion, however, is to show students what a mass spectrum looks like. The massspectra obtained in the original research shown in the video are available in the literature(Kratscher, et al., 1990; Kaldor, 1988). Seeing an example and knowing how it isinterpreted will be meaningful to students when they see the reference in the video.

Modeling carbon allotropesOnce students have explored some of the most easily observable properties of theallotropes of carbon, they construct and use models to help them to visualize thestructural characteristics that distinguish one allotrope from another. Guide them tofollow the instructions on the handout and answer the questions as they proceed.

Part 1 Modeling the buckyball:

Students will construct the NASA explores model (NASA, 2006), from the templateprovided. A quick verbal instruction or demonstration of procedure should be sufficient.

1. Cut around the perimeter of the buckyball template.

2. Cut along each dotted line to the star.

3. Cut out the shaded areas.

4. Beginning with the space labeled G in the upper right, apply glue using a gluestick, on the side where the G is printed. Slide this ring under the adjacentring, making a five-sided hole surrounded by six-sided shapes.

5. Repeat step 4 until the model is completed.

Once students have constructed their buckyball model, they will be able to draw arepresentation of their model on the report sheet or in their laboratory notebook.

Part 2 Modeling the carbon nanotube; the buckytube:

In this second part of the activity, students will model the three possible configurations of the carbon nanotube. Provide each group with three overhead transparencies of thehexagonal grid, representing a two dimensional grapheme sheet. Ask students to findthree different ways in which to curl the sheets into cylinders, making three differentarrangements of atoms. The models can be taped together using cellophane tape ormasking tape.

Once the models are constructed, their structural characteristics can be discussed; howthe three tubes are different, what is unique about the arrangement of atoms, how one canbe visually described relative to the others. Students can also be probed as to where thereare any other possible arrangements in which the tube could be rolled. Alternatives doexist, but the fact that the degree of offset in matching the two sides together can vary.


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Graphite, the black material in lead pencils, has little physical strength because its atomsare bonded to each other in only two dimensions ( sp2-hybridized geometry). Theresulting flat sheets readily slide over each other. The rings of graphite are aromatic and,

similar to the benzene ring, have de-localized pi electrons which can move freelythroughout the graphite sheet. This explains why graphite is the only nonmetal found innature that conducts electricity.

Follow-up (Race to Catch a Buckyball)

Evidence that there may be a new and unknown form of carbon arose from speculationfrom the UV and IR spectra from stars. Matching evidence from the laboratory to whatscientists had available gave support to the theory that there may be a new form of carbon, in a molecular shape never before seen. Soon after discovering that they hadcreated a new form of carbon in the laboratory, scientists began trying to create a modelof this molecule. Even when scientists were successful in creating the buckyball," theystill had not been able to isolate a pure sample or see a single molecule of Carbon 60.This exemplifies one role of the model in science, providing scientists a direction inwhich to look for new evidence. Ask the students to reflect on this process of developingand testing a theory from evidence and observation. What evidence was available toscientists that helped them create their model? Did all scientists view that evidenceequally? How did they evaluate and revise their ideas? How was the knowledge of science changing? What evidence helped then to confirm their theory? What evidencerequired the changing of their theory?

Alternate/supplemental activities/materials

There are other alternative models that can be used to make paper models of thebuckyball. One such model is available from Project SEEDSeed(http://www.seed.slb.com/en/scictr/lab/buckyball/index.htm). Sources cited above forcommercially available models also sell paper model templates.

Resources

Armfield, M. (2005). Carbon allotropes the same and not the same. Nanoscale Science

and Engineering Center, Northwestern University Research Experience for TeachersProgram, http://www.nsec.northwestern.edu

Arizona State University, IN-VSEE. (2006). Interactive Nano-visualization in Science &Engineering Education, The Allotropes of Carbon,http://invsee.asu.edu/Modules/carbon/question.htm

Castellini, O., Lisensky, G., Ehrlich, J., Zenner, G., & Crone, W. (2006). The structure &properties of carbon. The Science Teacher, 73 , 36-41.


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EDinformatics. (1999). What is the approximate diameter of a buckyball?http://www.edinformatics.com/math_science/fullerene.htm

Gale, Thomas, Thompson Corporation. (2005). Chemistry Explained,

http://www.chemistryexplained.com/A-Ar/Allotropes.htmlGreenwood, N. & Earnshaw, A. (1984). Chemistry of the Elements . New York:Pergamon Press.

Kratschmer, W., Lamb, L., Fostiropolos, K., & Huffman, D. (1990). Solid C60: A newform of carbon. Nature, 347 , 354-358.

Kroto, H., Heath, J., OBrien, S., Curl, R., Smalley, R. (1985). C 60: Buckminsterfullerene. Nature, 318 , 162-163.

NASA. Building Buckyballs . (2006).http://www.nasaexplores.com/show_912_student_st.php?id=030107112716

NOVA. (1995).Viewing guide, Race to Catch a Buckyball .http://www.pbs.org/wgbh/nova/teachers/viewing/2216_buckybal.html

Schwarzschild, B., (1996). Search and discovery: Nobel chemistry prize goes to Curl,Kroto and Smalley for discovering fullerenes. Physics Today, 49 , 19-21.

Zaugg, H. (1990). Growing diamonds. Chem Matters, April 10-16.

Further reading and watching

Growing Diamonds, ChemMatters , April, 1990

Nova Documentary, Diamond Deception.The melting of buckyball: http://www.pa.msu.edu/cmp/csc/simulC60melt.html

NASA Nanotechnology; http://www.ipt.arc.nasa.gov/nanotechnology.html

Museum of Science Boston, http://www.mos.org/cst-archive/article/4656/

allotropes+of+carbon teacher+packet july+2007

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