Fullerenes: An Overview Introduction The 1996 Nobel Prize for Chemistry has been won by Harold W. Kroto, Robert F. Curl and Richard E. Smalley for their discovery in 1985 of a new allotrope of carbon, in which the atoms are arranged in closed shells. The new form was found to have the structure of a truncated icosahedron, and was named Buckminsterfullerene, after the architect Buckminster Fuller who designed geodesic domes in the 1960's. Formerly, six crystalline forms of the element carbon were known, namely two kinds of graphite, two kinds of diamond, chaoit and carbon(VI). The latter two were discovered in 1968 and 1972. In 1990 physicists W. Krätschmer and D.R. Huffman for the first time produced isolable quantities of C60 by causing an arc between two graphite rods to burn in a helium atmosphere and extracting the carbon condensate so formed using an organic solvent.

The way was thus open for studying the chemical properties of C60 and other carbon clusters such as C70, C76, C78 and C84. New substances were produced from these compounds, with new and unexpected properties. An entirely new branch of chemistry developed, with consequences in such diverse areas as astrochemistry, superconductivity and materials chemistry/physics. Professor Sir Harold W. Kroto (University of Sussex) 1. Structure and physical properties of higher fullerenes pp.2-5 2. Production of fullerenes pp.6-8 3. Chemistry of fullerenes pp.8-10 1.) Structures and Physical Properties of Some Higher Fullerenes Fullerenes consist of 20 hexagonal and 12 pentagonal rings as the basis of an icosohedral symmetry closed cage structure. Each carbon atom is bonded to three others and is sp2 hybridised.

The C60 molecule has two bond lengths - the 6:6 ring bonds can be considered "double bonds" and are shorter than the 6:5 bonds.C60 is not "superaromatic" as it tends to avoid double bonds in the pentagonal rings, resulting in poor electron delocalisation. As a result, C60 behaves like an electron deficient alkene, and reacts readily with electron rich species. The geodesic and electronic bonding factors in the structure account for the stability of the molecule. In theory, an infinite number of fullerenes can exist, their structure based on pentagonal and hexagonal rings, constructed according to rules for making icosahedra. The structure of C60: "Buckminsterfullerene" The infra red spectrum of C60(left); 13C NMR spectrum of C60 (right): C60 only has four IR active vibrational bands, due to its icosohedral symmetry. The UV/visual spectrum chromatographically purified C60 (left); A mass spectrum showing the higher fullerenes present in carbon soot (right): Mass spectrometry has been widely used to study the fullerenes.

There is evidence for species as small as C20+, as well as stable peaks for the cluster ions C2n+ (where 2n>32). Infra red spectrum of C70 (left); UV/visual spectrum of C70 (right): Carbon 13 NMR spectrum of C70: C76 "Buckytubes" & "Buckyonions" Many fullerenes have now been discovered in carbon soot, uncovered by electron microscopy, including tubes of carbon many thousands of times long as they are wide, with the same icosahedral structure as the fullerenes. These have diameters as small as 2nm. Carbon "onions" have also been discovered, and consist of carbon cages one inside the other rather like Russian dolls. These carbon particles have millions of atoms, and many have been observed with dozens of concentric shells. Hypothetical structures have been postulated for carbon cages consisting of not pentagonal and hexagonal rings (like C60), but heptagonal (7 membered) rings. A helically coiled carbon nanotube Atomic resolution picture of a single walled carbon nanotube taken using ascanning tunneling microscope.

2.) The Production of Fullerenes The first method of production of fullerenes used laser vaporization of carbon in an inert atmosphere, but this produced microscopic amounts of fullerenes. In 1990, a new type of apparatus using an arc to vaporize graphite was developed in Germany by Kratschmer and Huffmann. Adapted Kratcshmer-Huffmann apparatus as used at Widener University Method for fullerene synthesis Pump down the system and introduce Helium gas into the chamber. Repeat (purge). Finally fill the bell-jar with about 100 Torr of Helium. Connect up the welding kit power supply Turn the on / off switch on the supply to the on position for 10 to 15 seconds. Afterwards there should be plenty of black soot like material produced inside the bell-jar. After a 5-10 min cool down period fill the bell-jar to atmospheric pressure. Take the bell-jar off and scrape the glass surfaces clean, collect all the material. 10 % of the soot should be made up of C60. The fullerenes in the soot are then extracted by solvation in a small amount of toluene.

After extraction, the solvent (toluene) is removed using a rotary evaporator, leaving behind a solid mixture of mostly C60 with small amounts of larger fullerenes. Pure C60 is obtained by liquid chromatography. The mixture is dissolved in toluene and pumped through a column of activated charcoal mixed with silica gel. The magenta C60 comes off first, followed by the red C70. The different color solutions are collected separately and the toluene removed using the rotary evaporator. A Mechanism for Fullerene Formation Although many mechanisms have been described, only the "pentagon road" appears to explain high yields of C60. This is described below, in an extract taken from an address by Professor Richard Smalley to the Robert A. Welch Foundation 39th Conference on Chemical Research: Nanophase Chemistry: Self-Assembly of Fullerene Tubes and Balls. "At the moment there is only one mechanism that appears to be consistent with yields of C60 as high as 30-40%. It is known as the Pentagon Road.

In this view, the yield is high because clustering continues in a hot enough region to permit the growing clusters to anneal to the minimum energy path: one where the graphene sheet (a) is made up solely of pentagons and hexagons, (b) has as many pentagons as possible, while (c) avoiding structures where two pentagons are adjacent. If the pentagon rule structures really are the lowest energy forms for any open carbon network, then one can readily imagine that high-yield synthesis of C60 may be possible. In principal, all one needs to do is adjust the conditions of the carbon cluster growth such that each open cluster has ample time to anneal into its favored pentagon rule structure before it grows further. This path through the kinetics is the Pentagon Road, and constitutes a mechanism of graphene-sheet self-assembly that leads to C60 in very high yield. The Pentagon Road must be the path that is followed in the high yield conditions.

This requires that the cluster growth temperature be high enough to anneal the open structures as they grow so that they follow the pentagon road, but that the temperature not be so high as to permit the extensive rearrangement and mounting of high activation barriers necessary to convert the open pentagon road structure to the closed fullerene. In the Krätschmer-Huffman (KH) experiment, carbon radicals are produced simply by slow evaporation of the surface of a resistively heated graphite rod. Here the carbon vapor density is far lower than that in pulsed laser vaporization, thus so too is the rate of clustering. Most critically, the rate of cooling of the condensing carbon vapor is much slower in the KH method. By adjusting the pressure of helium buffer gas around the evaporating graphite rods, one has at least coarse control over this rate of cooling and the clustering rate. At too low a pressure the carbon radicals migrate far away from the hot region around the resistively-heated rod and are too cold when they grow to the region of C60. But with just the right pressure of helium, the clustering in the critical size range occurs at just the right distance from the hot source that the temperature is optimal for the growing clusters to follow the Pentagon Road.

After the KH method was introduced, it was found at Rice that a simple ac or dc arc would produce C60 and the other fullerenes in good yield as well, and this is now the method used commercially. Even though the vaporization mechanism of a carbon arc differs markedly from that of a resistively heated carbon rod (because it involves a plasma) the optimum helium pressure for C60 formation is found to be very similar in each case. It is not so much the vaporization method that matters, but rather the conditions prevailing while the carbon vapor condenses. By adjusting the helium buffer gas pressure, one controls the rate of migration of the carbon vapor away from the hot graphite rod and thereby controls (at least crudely) the effective temperature and carbon radical density in the region where clusters in the size range near C60 are formed. The Pentagon Road mechanism is just one of many by which fullerenes can form, but it may be the only one capable of accounting for the single most telling fact of fullerene formation: that the overall C60 yield can be as high as 40% of all the carbon vaporized.

The Pentagon Road explains this as a consequence of annealing the open graphene sheets to their optimal open structure (given by the Pentagon Rule) at a rate faster than their growth, while avoiding rearrangement to a closed fullerene prior to the size of C60. It is a case of picking the reaction conditions to favor a particular product." Commercial production of Fullerenes The world's first computer controlled fullerene production plant is now operational at the MER corporation, who pioneered the first commercial production of fullerene and fullerene products. Commercial uses of fullerenes Although fullerenes are not yet used commercially, applications are being researched, such as catalytic methane activation to higher hydrocarbons funded by the US Dept of Energy. Other properties of fullerenes and their compounds such as superconductivity have yet to be exploited. 3.) Chemistry of the Fullerenes The reactions and reaction types of the fullerenes described below are merely examples of some recent work, not an exhaustive study. Redox chemistry C60 and C70 have similar properties, with six reversible one electron reductions to C60(6-) and C70(6-) having been observed. Oxidation of C60 and C70 is, however irreversible.

The first reduction for both fullerenes is ~1.0V for (Fc/Fc+), indicating they have electron accepting properties. C76 exhibits both electron donor/acceptor properties. C60 is an "alkene" C60 has a tendency of avoiding having double bonds within the pentagonal rings which makes electron delocalisation poor, and results in the fact that C60 is not "superaromatic". C60 behaves very much like an electron deficient alkene and readily reacts with electron rich species (see its organometallic reactions), but can also sometimes behave in a similar way to aromatic rings. Classes of fullerene compunds Compounds of fullerenes may be classed according to two different catagories: Exohedral (inside the cage) and Endohedral (outside the cage). Examples of the former include metals such as La enclosed in a C82 cage, and examples of the latter include transition metal complexes eg with Ir, as well as purely organic fragments bonded to the fullerene cage.

Fully brominated C60: C60Br(24) As noted above, fullerenes behave as electron deficient alkenes, and will react with electron rich species, such as halogens. Formation of C60Br24 by reactio of solid C60 with neat liquid bromine takes 5-8 days, but recently (Sept. 1996) a new method has been developed at Widener University, which reduces the reaction time to about an hour. Experimental : C60 (50mg) is placed in a closed conatiner with neat liquid bromine (5ml) and large gauge iron wire (ca. 1g), and stirred at room temp. for 1h. The excess liq. Br is then removed by vacuum evaporation, and the resulting solid treated with methanol to remove FeBr3 formed during the reaction. The remaining solid is then filtered and washed with methanol. Mechanism: The mechanism is thought to be similar to that of electrophilic aromatic substiution, i.e. the in-situ formation of FeBr3, (a Lewis acid) catalyzes the reaction by polarizing the Br2 molecule for electrophilic attack.

C60Br24 (ref. HADSIO) Endohedral Compounds When C60 was first discovered, new experiments were rapidly devised to test the C60 (as a closed cage structure) hypothesis. As the C60 structure is hollow, with room for one or more other atoms, attempts were made to enclose a metal atom. A graphite sheet was soaked with a solution of a metal salt (lanthanum chloride, LaCl3) and subjected to vaporisation-condensation experiments. Mass spectroscopic analysis of the clusters formed showed the presence of C60La+. These proved to be photoresistant, reinforcing the idea that metal atoms were "captured" inside the cage structure. The so called "shrink wrapping" experiment was then devised whereby ions of one size (or similar size) were captured in a magnetic trap and subjected to a laser pulse. The laser pulse causes the carbon cage to shrink by 2 carbon atoms at a time, until fragmentation ceased when pressure on the trapped metal atom is too big. The carbon cage now fits exactly around the metal atom.

For example, (forC60Cs+) this size is at (C48Cs+) and for (C60K+) it is at (C44K+). Below is an example of an endohedral metal fulleride, similar to that described above: La@C82 This field of fullerene research is very active,as this recent abstract shows: "Encapsulation of one or more metal atoms inside fullerene cages (endohedral metallofullerenes) is one of the most exciting topics in the fullerene science, since it could give rise to new species or materials with novel properties which are unexpected for hollow fullerenes. Recent important progress is marked by the successful isolation and purification of Sc@C-82, Y@C-82, La@C-82, Gd@C-82, La-2@C-80, and Sc-2@C-84 in large quantities. It is an interesting challenge to disclose how the properties of hollow fullerenes are modified upon endohedral metal-doping.

Recently, we have clarified the electronic structures and properties of endohedral metallofullerenes based on the theoretical calculations and have undertaken the first exohedral functionalization of metallofullerenes with organosilicon compound which can act as a mechanistic probe to clarify the electronic and chemical character of fullerenes. These successful exohedral derivatizations of endohedral metallofullerenes should open the way to a variety of new chemical entities with novel properties, enriching the chemistry of metallofullerenes." - Akasaka, T et al Journal of Synthetic Chemistry Japan 1996, vol 54, no.7 Allotropes of carbon Allotropes of carbon From Wikipedia, the free encyclopedia Eight allotropes of carbon : a) Diamond , b) Graphite , c) Lonsdaleite , d) C60 ( Buckminsterfullerene or buckyball ), e) C540, f) C70, g) Amorphous carbon , and h) single-walled carbon nanotube or buckytube . This is a list of the allotropes of carbon .

13 External links Diamond Diamond is one of the best known allotropes of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewelry. Diamond is the hardest known natural mineral , which makes it an excellent abrasive and makes it hold polish and luster extremely well. No known naturally occurring substance can scratch, let alone cut, a diamond. The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones and known as bort , are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 400 million carats (80,000 kg) of synthetic diamonds are produced annually for industrial useďż˝nearly four times the mass of natural diamonds mined over the same period.

The dominant industrial use of diamond is in cutting, drilling (drill bits), grinding (diamond edged cutters), and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality can find an industrial use. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil ), high-performance bearings , and limited use in specialized windows . With the continuing advances being made in the production of synthetic diamond, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics . Significant research efforts in Japan , Europe , and the United States are under way to capitalize on the potential offered by diamond's unique material properties, combined with increased quality and quantity of supply starting to become available from synthetic diamond manufacturers. Each carbon atom in a diamond is covalently bonded to four other carbons in a tetrahedron. These tetrahedrons together form a 3-dimensional network of puckered six-membered rings of atoms.

This stable network of covalent bonds and the three dimensional arrangement of bonds is the reason that diamond is so strong. Graphite Graphite (named by Abraham Gottlob Werner in 1789 , from the Greek γράφειν: "to draw/write", for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor, and can be used, for instance, as the material in the electrodes of an electrical arc lamp. Graphite holds the distinction of being the most stable form of carbon under standard conditions . Therefore, it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Graphite is able to conduct electricity , due to delocalization of the pi bond electrons above and below the planes of the carbon atoms. These electrons are free to move, so are able to conduct electricity. However, the electricity is only conducted along the plane of the layers. In diamond all four outer electrons of each carbon atom are 'localised' between the atoms in covalent bonding. The movement of electrons is restricted and diamond does not conduct an electric current.

In graphite, each carbon atom uses only 3 of its 4 outer energy level electrons in covalently bonding to three other carbon atoms in a plane. Each carbon atom contributes one electron to a delocalised system of electrons that is also a part of the chemical bonding. The delocalised electrons are free to move throughout the plane. For this reason, graphite conducts electricity along the planes of carbon atoms, but does not conduct in a direction at right angles to the plane. Graphite powder is used as a dry lubricant . Although it might be thought that this industrially important property is due entirely to the loose interlamellar coupling between sheets in the structure, in fact in a vacuum environment (such as in technologies for use in space ), graphite was found to be a very poor lubricant. This fact led to the discovery that graphite's lubricity is due to adsorbed air and water between the layers, unlike other layered dry lubricants such as molybdenum disulfide . Recent studies suggest that an effect called superlubricity can also account for this effect.

When a large number of crystallographic defects bind these planes together, graphite loses its lubrication properties and becomes what is known as pyrolytic carbon , a useful material in blood-contacting implants such as prosthetic heart valves . Natural and crystalline graphites are not often used in pure form as structural materials due to their shear-planes, brittleness and inconsistent mechanical properties. In its pure glassy (isotropic) synthetic forms, pyrolytic graphite and carbon fiber graphite is an extremely strong, heat-resistant (to 3000 ďż˝C) material, used in reentry shields for missile nosecones, solid rocket engines, high temperature reactors , brake shoes and electric motor brushes. Intumescent or expandable graphites are used in fire seals, fitted around the perimeter of a fire door. During a fire the graphite intumesces (expands and chars) to resist fire penetration and prevent the spread of fumes. A typical start expansion temperature (SET) is between 150 and 300 degrees Celsius. Density: its specific gravity is 2.3 which makes it lighter than diamond. Effect of heat: it is the most stable allotrope of carbon.

At a temperature of 2500 degree Celsius, it can be transformed into diamond. At about 700 degree Celsius it burns in pure oxygen forming carbon dioxide. Chemical activity: it is slightly more reactive than diamond. This is because the reactants are able to penetrate between the hexagonal layers of carbon atoms in graphite. It is unaffected by ordinary solvents, dilute acids, or fused alkalis. However, chromic acid oxidises it to carbon dioxide. Amorphous carbon Amorphous carbon is the name used for carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. While entirely amorphous carbon can be made, natural amorphous carbon (such as soot) actually contains microscopic crystals of graphite , [1] sometimes diamond [2] . On the macroscopic scale, amorphous carbon has no definite structure as it conisists of small irregular cystals, but on the nanomicroscopic scale, we can see it is made of regularly arranged carbon atoms. Coal and soot are both informally called amorphous carbon.

However, both are products of pyrolysis (the process of decomposing a substance by the action of heat), which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade, anthracite , is about 90 percent carbon and 10% other elements. Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal that is around 55 percent carbon. Buckminsterfullerenes This box: view ďż˝ talk ďż˝ edit Buckyballs Spherical fullerenes are also called buckyballs. Carbon nanotubes Carbon nanotubes, also called buckytubes, are cylindrical carbon molecules with novel properties that make them potentially useful in a wide variety of applications (e.g., nano-electronics, optics , materials applications, etc.). They exhibit extraordinary strength, unique electrical properties, and are efficient conductors of heat . Inorganic nanotubes have also been synthesized.

A nanotube (also known as a buckytube) is a member of the fullerene structural family, which also includes buckyballs . Whereas buckyballs are spherical in shape, a nanotube is cylindrical , with at least one end typically capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 50,000 times smaller than the width of a human hair), while they can be up to several centimeters in length. There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Carbon nanobuds Computer models of stable NanoBud structures Carbon NanoBuds are a newly discovered allotrope of carbon in which fullerene like "buds" are covalently attached to the outer sidewalls of the carbon nanotubes . This hybrid material has useful properties of both fullerenes and carbon nanotubes. In particular, they have been found to be exceptionally good field emitters.

Aggregated diamond nanorods Aggregated diamond nanorods, or ADNRs, are an allotrope of carbon believed to be the least compressible material known to humankind, as measured by its isothermal bulk modulus ; aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442 GPa. ADNRs are also 0.3% denser than regular diamond. The ADNR material is also harder than type IIa diamond and ultrahard fullerite . Glassy carbon Glassy carbon is a class of non-graphitizing carbon which is widely used as an electrode material in electrochemistry , as well as for high temperature crucibles and as a component of some prosthetic devices. It was first produced by workers at the laboratories of The General Electric Company , UK , in the early 1960s, using cellulose as the starting material. A short time later, Japanese workers produced a similar material from phenolic resin . It was first produced by Bernard Redfern in the mid 1950's at the laboratories of The Carborundum Company, Trafford , UK .

He set out to develop a polymer matrix to mirror a diamond structure and discovered a resole (phenolic) resin that would, with special preparation, set without a catalyst. Using this resin the first glassy carbon was produced. Patents were filed some of which were withdrawn in the interests of national security. Original research samples of resin and product exist. The preparation of glassy carbon involves subjecting the organic precursors to a series of heat treatments at temperatures up to 3000oC. Unlike many non-graphitizing carbons, they are impermeable to gases and are chemically extremely inert, especially those which have been prepared at very high temperatures. It has been demonstrated that the rates of oxidation of certain glassy carbons in oxygen, carbon dioxide or water vapour are lower than those of any other carbon. They are also highly resistant to attack by acids. Thus, while normal graphite is reduced to a powder by a mixture of concentrated sulfuric and nitric acids at room temperature, glassy carbon is unaffected by such treatment, even after several months. Carbon nanofoam Carbon nanofoam is the fifth known allotrope of carbon discovered in 1997 by Andrei V.

Rode and co-workers at the Australian National University in Canberra . It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web. Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite -like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the opposite of what happens in the case of buckminsterfullerenes , in which carbon sheets are given positive curvature by the inclusion of pentagons . The large-scale structure of carbon nanofoam is similar to that of an aerogel , but with 1% of the density of previously produced carbon aerogels - only a few times the density of air at sea level . Unlike carbon aerogels, carbon nanofoam is a poor electrical conductor . Lonsdaleite (hexagonal diamond) Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond , believed to form when meteoric graphite falls to Earth . The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice .

Lonsdaleite was first identified from the Canyon Diablo meteorite at Barringer Crater (also known as Meteor Crater) in Arizona . It was first discovered in 1967 . Lonsdaleite occurs as microscopic crystals associated with diamond in the Canyon Diablo meteorite; Kenna meteorite, New Mexico ; and Allan Hills (ALH) 77283, Victoria Land, Antarctica meteorite. It has also been reported from the Tunguska impact site , Russia . Linear Acetylenic Carbon (LAC) Chemists in the USA have recently reported (ca 1995) an allotrope of carbon consisting of long chains of carbon atoms where the alternate carbon-carbon bonds are of different lengths; and consist of C-C bonds and C≡C bonds. The same polymer was synthesized in early 1960s by group of Soviet chemists and was called carbyne (Russian: карбин). It appeared to be a semiconductor that is very sensitive to light, thus it was suggested to use it in photodiodes and similar devices.

Carbyne, or polyyne, is also another name for Linear Acetylenic Carbon [1] (LAC) the carbon allotrope that has the chemical structure [2] -(C:::C)n- .Carbon in this modification is linear with sp orbital hybridisation , and is a polymer with alternating single and triple bonds. This type of carbyne is of considerable interest to nanotechnology as its Young's modulus is forty times that of diamond [3] . Variability of carbon Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure. The system of carbon allotropes spans an astounding range of extremes, considering that they are all merely structural formations of the same element. Between diamond and graphite: Diamond crystallizes in the cubic system but graphite crystallizes in the hexagonal system . Diamond is hardest mineral known to man (10 on Mohs scale ), but graphite is one of the softest (1 - 2 on Mohs scale ). Diamond is the ultimate abrasive, but graphite is a very good lubricant. Diamond is an excellent electrical insulator, but graphite is a conductor of electricity.

Diamond is an excellent thermal conductor, but some forms of graphite are used for thermal insulation (i.e. heatshields and firebreaks) Other possible forms Chaoite is a mineral believed to have been formed in meteorite impacts. It has been described as slightly harder than graphite with a reflection colour of grey to white. However, the existence of carbyne phases is disputed ďż˝ see the entry on chaoite for details. Metallic carbon: Theoretical studies have shown that carbon (diamond) when brought at enormous pressure, there are regions in the phase diagram where it's metallic. [4] It seems that it can also become superconducting at very low temperatures (4 kelvins). [5] Hexagonite: in theory, instead of having the 6-arom rings of graphite, one sp carbon atom could be inserted between each of the 6 sp2 atoms. [6] Prismane C8 is another possible metastable form. Carbon Allotropes — NanoScienceWorks Main article: Diamond Diamond is one of the best known allotropes of carbon, whose hardness and high dispersion of light make it useful for industrial applications and jewelry.

Diamond is the hardest known natural mineral , making it an excellent abrasive and also means a diamond holds its polish extremely well and retains luster. The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and heat conductivity, making many of the gemological characteristics of diamond, including clarity and color, mostly irrelevant. This helps explain why 80% of mined diamonds (equal to about 100 million carats or 20,000 kg annually), unsuitable for use as gemstones and known as bort , are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 400 million carats (80,000 kg) of synthetic diamonds are produced annually for industrial use—nearly four times the mass of natural diamonds mined over the same period. The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most uses of diamonds in these technologies do not require large diamonds; in fact, most diamonds that are gem-quality except for their small size, can find an industrial use.

Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil ), high-performance bearings , and limited use in specialized windows . With the continuing advances being made in the production of synthetic diamond, future applications are beginning to become feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips from, or the use of diamond as a heat sink in electronics . Significant research efforts in Japan , Europe , and the United States are under way to capitalize on the potential offered by diamond's unique material properties, combined with increased quality and quantity of supply starting to become available from synthetic diamond manufacturers. Each carbon atom in diamond is covalently bonded to four other carbons in a tetrahedron. These tetrahedrons together form a 3-dimensional network of puckered six-membered rings of atoms. This stable network of covalent bonds and the three dimensional arrangement of bonds that diamond is so strong.

Graphite Main article: Graphite Graphite (named by Abraham Gottlob Werner in 1789 , from the Greek γραφειν: "to draw/write", for its use in pencils) is one of the most common allotropes of carbon. Unlike diamond, graphite is a conductor, and can be used, for instance, as the material in the electrodes of an electrical arc lamp. Graphite holds the distinction of being the most stable form of solid carbon ever discovered. Graphite is able to conduct electricity due to the unpaired fourth electron in each carbon atom. This unpaired 4th electron forms delocalised planes above and below the planes of the carbon atoms. These electrons are free to move, so are able to conduct electricity. However, the electricity is only conducted within the plane of the layers. Graphite powder is used as a dry lubricant . Although it might be thought that this industrially important property is due entirely to the loose interlamellar coupling between sheets in the structure, in fact in a vacuum environment (such as in technologies for use in space ), graphite was found to be a very poor lubricant.

This fact lead to the discovery that graphite's lubricity is due to adsorbed air and water between the layers, unlike other layered dry lubricants such as molybdenum disulfide . Recent studies suggest that an effect called superlubricity can also account for this effect. When a large number of crystallographic defects bind these planes together, graphite loses its lubrication properties and becomes what is known as pyrolytic carbon , a useful material in blood-contacting implants such as prosthetic heart valves . Natural and crystalline graphites are not often used in pure form as structural materials due to their shear-planes, brittleness and inconsistent mechanical properties. In its pure glassy (isotropic) synthetic forms, pyrolytic graphite and carbon fiber graphite is an extremely strong, heat-resistant (to 3000 °C) material, used in reentry shields for missile nosecones, solid rocket engines, high temperature reactors , brake shoes and electric motor brushes. Intumescent or expandable graphites are used in fire seals, fitted around the perimeter of a fire door. During a fire the graphite intumesces (expands and chars) to resist fire penetration and prevent the spread of fumes.

A typical start expansion temperature (SET) is between 150 and 300 degrees Celsius. Amorphous carbon Main article: Amorphous carbon Amorphous carbon is the name used for carbon that does not have any crystalline structure. As with all glassy materials, some short-range order can be observed, but there is no long-range pattern of atomic positions. While entirely amorphous carbon can be made, most of the material described as "amorphous" actually contains crystallites of graphite [1] or diamond [2] with varying amounts of amorphous carbon holding them together, making them technically polycrystalline or nanocrystalline materials. Commercial carbon also usually contains significant quantities of other elements, which may form crystalline impurities. Coal and soot are both informally called amorphous carbon. However, both are products of pyrolysis , which does not produce true amorphous carbon under normal conditions. The coal industry divides coal up into various grades depending on the amount of carbon present in the sample compared to the amount of impurities. The highest grade, anthracite , is about 90 percent carbon and 10% other elements.

Bituminous coal is about 75-90 percent carbon, and lignite is the name for coal that is around 55 percent carbon. Fullerenes Main article: Fullerene The fullerenes are recently-discovered allotropes of carbon named after the scientist and architect Richard Buckminster Fuller , but were discovered in 1985 by a team of scientists from Rice University and the University of Sussex , three of whom were awarded the 1996 Nobel Prize in Chemistry . They are molecules composed entirely of carbon, which take the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are sometimes called buckyballs, while cylindrical fullerenes are called buckytubes or nanotubes. As of the early twenty-first century, the chemical and physical properties of fullerenes are still under heavy study, in both pure and applied research labs. In April 2003, fullerenes were under study for potential medicinal use — binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma.

Fullerenes are similar in structure to graphite, which is composed of a sheet of linked hexagonal rings, but they contain pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar. Carbon nanotubes Main article: Carbon nanotube Carbon nanotubes are cylindrical carbon molecules with novel properties that make them potentially useful in a wide variety of applications (e.g., nano-electronics, optics , materials applications, etc.). They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat . Inorganic nanotubes have also been synthesized. A nanotube (also known as a buckytube) is a member of the fullerene structural family, which also includes buckyballs . Whereas buckyballs are spherical in shape, a nanotube is cylindrical , with at least one end typically capped with a hemisphere of the buckyball structure. Their name is derived from their size, since the diameter of a nanotube is on the order of a few nanometers (approximately 50,000 times smaller than the width of a human hair), while they can be up to several centimeters in length.

There are two main types of nanotubes: single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Aggregated diamond nanorods Main article: Aggregated diamond nanorods Aggregated diamond nanorods, or ADNRs, are an allotrope of carbon believed to be the least compressible material known to humankind, as measured by its isothermal bulk modulus ; aggregated diamond nanorods have a modulus of 491 gigapascals (GPa), while a conventional diamond has a modulus of 442 GPa. ADNRs are also 0.3% denser than regular diamond. The ADNR material is also harder than type IIa diamond and ultrahard fullerite . Glassy carbon Main article: Glassy carbon Glassy carbon is a class of non-graphitizing carbon which is widely used as an electrode material in electrochemistry , as well as for high temperature crucibles and as a component of some prosthetic devices. It was first produced by workers at the laboratories of The General Electric Company , UK, in the early 1960s, using cellulose as the starting material.

A short time later, Japanese workers produced a similar material from phenolic resin . The preparation of glassy carbon involves subjecting the organic precursors to a series of heat treatments at temperatures up to 3000oC. Unlike many non-graphitizing carbons, they are impermeable to gases and are chemically extremely inert, especially those which have been prepared at very high temperatures. It has been demonstrated that the rates of oxidation of certain glassy carbons in oxygen, carbon dioxide or water vapour are lower than those of any other carbon. They are also highly resistant to attack by acids. Thus, while normal graphite is reduced to a powder by a mixture of concentrated sulphuric and nitric acids at room temperature, glassy carbon is unaffected by such treatment, even after several months. Carbon nanofoam Main article: Carbon nanofoam Carbon nanofoam is the fifth known allotrope of carbon discovered in 1997 by Andrei V. Rode and co-workers at the Australian National University in Canberra . It consists of a low-density cluster-assembly of carbon atoms strung together in a loose three-dimensional web.

Each cluster is about 6 nanometers wide and consists of about 4000 carbon atoms linked in graphite -like sheets that are given negative curvature by the inclusion of heptagons among the regular hexagonal pattern. This is the opposite of what happens in the case of buckminsterfullerenes , in which carbon sheets are given positive curvature by the inclusion of pentagons . The large-scale structure of carbon nanofoam is similar to that of an aerogel , but with 1% of the density of previously produced carbon aerogels - only a few times the density of air at sea level . Unlike carbon aerogels, carbon nanofoam is a poor electrical conductor . Lonsdaleite Main article: Lonsdaleite Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond , believed to form when meteoric graphite falls to Earth . The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice . Lonsdaleite was first identified from the Canyon Diablo meteorite at Barringer Crater (also known as Meteor Crater) in Arizona . It was first discovered in 1967 .

Lonsdaleite occurs as microscopic crystals associated with diamond in the Canyon Diablo meteorite; Kenna meteorite, New Mexico ; and Allan Hills (ALH) 77283, Victoria Land, Antarctica meteorite. It has also been reported from the Tunguska impact site, Russia . Chaoite Main article: Chaoite Chaoite is a mineral believed to have been formed in meteorite impacts. It has been described as slightly harder than graphite with a reflection colour of grey to white. However, the existence of carbyne phases is disputed – see the entry on chaoite for details. Variability of carbon The system of carbon allotropes spans an astounding range of extremes, considering that they are all merely structural formations of the same element. Between diamond and graphite Diamond is hardest mineral known to man (10 on Mohs scale), but graphite is one of the softest (1 - 2 on Mohs scale). Diamond is the ultimate abrasive, but graphite is a very good lubricant. Diamond is an excellent electrical insulator, but graphite is a conductor of electricity. Diamond is usually transparent, but graphite is opaque. Diamond crystallizes in the isometric system but graphite crystallizes in the hexagonal system .

Between amorphous carbon and nanotubes Amorphous carbon is among the easiest materials to synthesize, but carbon nanotubes are extremely expensive to make. Amorphous carbon is completely isotropic , but carbon nanotubes are among the most anisotropic materials ever produced. Laser-induced graphitization of fullerite | DeepDyve Try 2 weeks free now Laser-induced graphitization of fullerite Ferretti, M.; Parisini, A.; Manfredini, M.; Milani, P. Ordered graphitic micro- and nano-structures have been produced by infrared pulsed laser irradiation of fullerite in air and in helium. A characterization of the irradiated regions has been performed by scanning electron microscopy and transmission electron microscopy. We have observed the formation of linear graphitic braids and hollow polyhedral onions. Our experiments provide new elements for a detailed understanding of fullerene disruption and coalescence of fullerene precursors under various physico-chemical conditions. The relevance of these processes for the synthesis of different carbon allotropes is also addressed. Chemical Physics Letters Elsevier Loading next page...

IB Chemistry higher level notes: Allotropes of carbon IB syllabus for first examinations 2016 14.4 - Allotropes of carbon 14.4.1 Describe and explain the structures and properties of diamond, graphite and fullerene. Students should recognize the type of hybridization present in each allotrope and the delocalization of electrons in graphite and C60 fullerene. Allotropy Allotropes are different physical forms of the same element. All elements are made up uniquely of their own atoms and therefore any physical differences must be a consequence of how the atoms are joined together - their arrangement within the bulk structure. Many elements exhibit allotropy as there are often varous ways in which the atoms can be linked together into molecules and also different ways in which the molecules can be arranged to make larger structures.

In the case of carbon, the atoms form either giant macromolecular structures (diamond and graphite) in which all of the atoms in the bulk structure are joined together by covalent bonds making giant molecules, or smaller molecules (buckminster fullerene) in which there are only discrete molecules made up of 60 carbons in a structure resembling a football (hence the nickname 'bucky balls') Diamond Each carbon in a diamond crystal is bonded to four other carbon atoms making a giant macromolecular array (lattice). As each carbon has four single bonds it is sp3 hybridised and has tetrahedral bond angles of 109º 28' Properties of diamond Hard Many strong covalent bonds holding the structure together Click on the image with the left mouse button and drag to get a different view. (if you can't see the image you have to download chime ) Brittle All of the bonds are directional and stress will tend to break the structure (In a malleable substance, such as for example a metal, the bonding is non-directional and can still act if the particles are displaced with respect to one another). Insulator All of the valence (outer shell) electrons are used in bonding.

The bonds are sigma and the electrons are located between the two carbon nuclei being bonded together. None of the electrons are free to move Insoluble There are only very weak Van der Waal's attractions between the carbon atoms and the water molecules whereas the carbon atoms are bodned very tightly to one another. Very high melting point Many strong covalent bonds holding the structure together - it requires massive amounts of energy to pull it apart Graphite Again the carbon atoms are bonded together to make a giant structure but in this case all of the carbons are bonded to only three neighbour and are sp2 hybridised. As the sp2 hybridisation results in planar structures, there are giant 2 dimensional layers of carbon atoms and each layer is only weakly linked to the next layer by Van der Waal's forces. Physical properties of graphite explained by considering the structure and bonding Property Graphite structure Soft and slippery Many strong covalent bonds holding the structure together but only in 2 dimensions. The layers are free to slide easily over one another. Graphite powder is used as a lubricant. Click on the image with the left mouse button and drag to get a different view.

(if you can't see the image you have to download chime ) Brittle All of the bonds are directional within a layer and stress across a layer will tend to break them. Graphite rods used for electrolysis easily break when dropped. Electrical conductor Only three of the valence (outer shell) electrons are used in sigma bonding. The other electron is in a 'p' orbital which can overlap laterally with neighbouring 'p' orbitals making giant molecular pi orbitals that extend over the whole of each layer. Electrons are free to move within these delocalised pi orbitals. Insoluble in water. There are only very weak Van der Waal's attractions between the carbon atoms and the water molecules whereas the carbon atoms are bonded very tightly to one another. V. high melting point Many strong covalent bonds holding the layers together - it requires massive amounts of energy to pull it apart Fullerenes These are small molecules of carbon in which the giant structure is closed over into spheres of atoms (bucky balls) or tubes (sometimes caled nano-tubes). The smallest fullerene has 60 carbon atoms arranged in pentagons and hexagons like a football. This is called Buckminsterfullerene.

The name 'buckminster fullerene' comes from the inventor of the geodhesic dome (Richard Buckminster Fuller) which has a similar structure to a fullerene. Fullerenes were first isolated from the soot of chimineys and extracted from solvents as red crystals. The bonding has delocalised pi molecular orbitals extending throughout the structure and the carbon atoms are a mixture of sp2 and sp3 hybridised systems. Fullerenes are insoluble in water but soluble in methyl benzene. They are non- conductors as the individual molecules are only held to each other by weak van der Waal's forces. Buckminster fullerene Structure As the molecule is totally symmetrical with all bond lengths and angles being equal, it is likely/inevitable that the hybridisation of the carbon atoms is somewhere between that of sp2 and sp3. Another example of a theory (hybridisation in this case) having to be modified to accomodate the observed experimental data. Physical properties of fullerenes explained by considering the structure and bonding Property The Element Carbon -- Carbon Atom 14N SI units & STP are used except where noted.

Carbon (Wiktionary:carbon) is the chemical element in the periodic table that has the symbol C and atomic number 6. An abundant nonmetallic , tetravalent element, carbon has several allotropic forms : diamonds (hardest known mineral ). Binding structure: 4 electrons in 3-dimensional so-called sp3-orbitals graphite (one of the softest substances). Binding structure: 3 electrons in 2-dimensional sp2-orbitals and 1 electron in s-orbitals. Covalent bound sp1 orbitals are of chemical interest only. Fullerite ( fullerenes ) are nanometer-scale molecules. In the simple form 60 carbon atoms form a graphitic layer which is bent to a 3-dimensional structure, similar to a soccer ball. Lamp black consists of small graphitic areas. These areas are randomly distributed, so the whole structure is isotropic. So-called 'glassy carbon' is isotropic and as strong as glass. Unlike normal graphite, the graphitic layers are not arranged like pages in a book, but are crumpled like crumpled paper. Carbon fibers are similar to glassy carbon.

Under special treatment (stretching of organic fibers and carbonization) it is possible to arrange the carbon planes in direction of the fiber. Perpendicular to the fiber axis there is no orientation of the carbon planes. The result are fibers with a higher specific strength than steel. Carbon occurs in all organic life and is the basis of organic chemistry . This nonmetal also has the interesting chemical property of being able to bond with itself and a wide variety of other elements, forming nearly 10 million known compounds. When united with oxygen it forms carbon dioxide which is absolutely vital to plant growth. When united with hydrogen , it forms various compounds called hydrocarbons which are essential to industry in the form of fossil fuels . When combined with both oxygen and hydrogen it can form many groups of compounds including fatty acids , which are essential to life, and esters, which give flavor to many fruits. The isotope carbon-14 is commonly used in radioactive dating . Notable characteristics Carbon is a remarkable element for many reasons. Its different forms include one of the softest (graphite) and one of the hardest (diamond) substances known to man.

Moreover, it has a great affinity for bonding with other small atoms , including other carbon atoms, and its small size makes it capable of forming multiple bonds. Because of these properties, carbon is known to form nearly ten million different compounds. Carbon compounds form the basis of all life on Earth and the carbon-nitrogen cycle provides some of the energy produced by the sun and other stars . Carbon was not created in the big bang due to the fact that it needs a triple collision of alpha particles ( helium nuclei) to be produced. The universe initially expanded and cooled too fast for that to be possible. It is produced, however, in the interior of stars in the horizontal branch , where stars transform a helium core into carbon by means of the triple-alpha process . Applications Carbon is a vital component of all known living systems, and without it life as we know it could not exist (see carbon chauvinism ). The major economic use of carbon is in the form of hydrocarbons, most notably the fossil fuels methane gas and crude oil . Crude oil is used by the petrochemical industry to produce, amongst others, petroleum , gasoline and kerosene , through a distillation process, in so-called refineries .

Crude oil forms the raw material for many synthetic substances, many of which are collectively called plastics . Other uses: Carbon is used for control rods in nuclear reactors . Graphite carbon in a powdered, caked form is used as charcoal for cooking , artwork and other uses. Charcoal pills are used in medicine in pill or powder form to adsorb toxins or poisons from the digestive system. The chemical and structural properties of fullerenes, in the form of carbon nanotubes , has promising potential uses in the nascent field of nanotechnology. History Carbon ( Latin carbo meaning "charcoal") was discovered in prehistory and was known to the ancients, who manufactured it by burning organic material in insufficient oxygen (making charcoal ). Diamonds have long been considered rare and beautiful. The last-known allotrope of carbon, fullerenes , were discovered as byproducts of molecular beam experiments in the 1980's. Allotropes Four allotropes of carbon are known to exist: amorphous, graphite , diamond and fullerenes .

The discovery of a fifth form was announced on March 22 , 2004 [1] ( In its amorphous form, carbon is essentially graphite but not held in a crystalline macrostructure. It is, rather, present as a powder which is the main constituent of substances such as charcoal and lamp black ( soot ). At normal pressures carbon takes the form of graphite , in which each atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons . The two known forms of graphite, alpha (hexagonal) and beta ( rhombohedral ), both have identical physical properties, except for their crystal structure. Graphites that naturally occur have been found to contain up to 30% of the beta form, when synthetically-produced graphite only contains the alpha form. The alpha form can be converted to the beta form through mechanical treatment and the beta form reverts back to the alpha form when it is heated above 1000 ï¿½ C . Because of the delocalization of the pi-cloud , graphite conducts electricity .

The material is soft and the sheets, frequently separated by other atoms, are held together only by van der Waals forces , so easily slip past one another. At very high pressures carbon has an allotrope called diamond , in which each atom is bonded to four others. Diamond has the same cubic structure as silicon and germanium and, thanks to the strength of the carbon-carbon bonds , is together with the isoelectronic boron nitride (BN) the hardest substance in terms of resistance to scratching. The transition to graphite at room temperature is so slow as to be unnoticeable. Under some conditions, carbon crystallizes as Lonsdaleite , a form similar to diamond but hexagonal. Fullerenes have a graphite-like structure, but instead of purely hexagonal packing, also contain pentagons (or possibly heptagons) of carbon atoms, which bend the sheet into spheres, ellipses or cylinders. The properties of fullerenes (also called "buckyballs" and "buckytubes") have not yet been fully analyzed. All the names of fullerenes are after Buckminster Fuller , developer of the geodesic dome , which mimics the structure of "buckyballs".

Occurrence There are nearly ten million carbon compounds that are known to science and many thousands of these are vital to life processes and very economically important organic-based reactions. This element is abundant in the sun , stars , comets , and in the atmospheres of most planets . Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk . In combination with other elements, carbon is found the earth's atmosphere and dissolved in all bodies of water. With smaller amounts of calcium , magnesium , and iron , it is a major component of very large masses carbonate rock ( limestone , dolomite , marble etc.). When combined with hydrogen , carbon form coal , petroleum , and natural gas which are called hydrocarbons. Natural diamonds occur in the mineral kimberlite found in ancient volcanic "necks," or "pipes". Most diamond deposits are in Africa , notably in South Africa , Namibia , Botswana , the Republic of the Congo and Sierra Leone . There are also deposits in Canada , the Russian Arctic , Brazil and in Northern and Western Australia . Inorganic compounds (See also organic chemistry .) The most prominent oxide of carbon is carbon dioxide , CO2.

This is a minor component of the Earth's atmosphere , produced and used by living things, and a common volatile elsewhere. In water it forms trace amounts of carbonic acid , H2CO3, but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite . Carbon disulfide , CS2, is similar. The other oxides are carbon monoxide , CO, and the uncommon carbon suboxide, C3O2. Carbon monoxide is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar , resulting in a tendency to bind permanently to hemoglobin molecules, so that the gas is highly poisonous. Cyanide , CN-, has a similar structure and behaves a lot like a halide ion; the nitride cyanogen , (CN)2, is related. With strong metals carbon forms either carbides, C-, or acetylides, C22-; these are associated with methane and acetylene , both incredibly pathetic acids .

All in all, with an electronegativity of 2.5, carbon prefers to form covalent bonds . A few carbides are covalent lattices, like carborundum , SiC, which resembles diamond . Carbon chains Itï¿½s the atomic structure of hydrocarbons in which a series of carbon atoms, saturated by hydrogen atoms, form a chain. Volatile oils have shorter chains. Fats have longer chain lengths, and waxes have extremely long chains. Carbon cycle The continuous process of combining and releasing carbon and oxygen thereby storing and emitting heat and energy. Catabolism + anabolism = metabolism . See carbon cycle . Isotopes In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 for basis for atomic weights . Carbon-14 is a radioisotope with a half-life of 5715 years and has been used extensively for radiocarbon dating wood, archaeological sites and specimens. Carbon has two stable, naturally-occurring isotopes: C-12 (98.89%) and C-13 (1.11%). Ratios of these isotopes are reported in ?

relative to the standard VPDB (Vienna Pee Dee Belemnite from the Peedee Formation of South Carolina). The d C-13 of the atmosphere is -7?. During photosynthesis , the carbon that becomes fixed in plant tissue is significantly depleted in C-13 relative to the atmosphere. There is two mode distribution in the dC-13 values of terrestrial plants resulting from differences in the photosynthetic reaction used by the plant. Most terrestrial plants are C3 pathway plants and have dC-13 values range from -24 to -34?. A second category of plants ( C4 pathway plants ), composed of aquatic plants, desert plants, salt marsh plants, and tropical grasses, have dC-13 values that range from -6 to -19. An intermediate group ( CAM plants ) composed of algae and lichens has dC-13 values range from -12 to -23?. The dC-13 of plants and organisms can provide useful information about sources of nutrients and food web relations. Precautions Compounds of carbon have a wide range of toxic action.

Carbon monoxide (C O ), which is present in the exhaust of combustion engines, and cyanide (CN-), which is sometimes in mining pollution, are extremely toxic to mammals . Many other carbon compounds are not toxic and are in fact absolutely essential for life. Organic gases such as ethene (CH2=CH2), ethyne (HCCH), and methane (CH4) are dangerously explosive and flammable when mixed with air.

Question: Fullerite is a man-made allotrope of which chemical element?
Answer: CARBON