Allotropy
![](https://upload.wikimedia.org/wikipedia/commons/thumb/f/f9/Diamond_and_graphite.jpg/193px-Diamond_and_graphite.jpg)
Allotropyorallotropism(fromAncient Greekἄλλος(allos)'other' andτρόπος(tropos)'manner, form') is the property of somechemical elementsto exist in two or more different forms, in the same physicalstate,known asallotropesof the elements. Allotropes are different structural modifications of an element: theatomsof the element arebondedtogether in different manners.[1] For example, theallotropes of carbonincludediamond(the carbon atoms are bonded together to form acubic latticeoftetrahedra),graphite(the carbon atoms are bonded together in sheets of ahexagonal lattice),graphene(single sheets of graphite), andfullerenes(the carbon atoms are bonded together in spherical, tubular, or ellipsoidal formations).
The termallotropyis used for elements only, not forcompounds.The more general term, used for any compound, ispolymorphism,although its use is usually restricted to solid materials such as crystals. Allotropy refers only to different forms of an element within the same physicalphase(the state of matter, such as asolid,liquidorgas). The differences between these states of matter would not alone constitute examples of allotropy. Allotropes of chemical elements are frequently referred to aspolymorphsor asphasesof the element.
For some elements, allotropes have different molecular formulae or different crystalline structures, as well as a difference in physical phase; for example, twoallotropes of oxygen(dioxygen,O2,andozone,O3) can both exist in the solid, liquid and gaseous states. Other elements do not maintain distinct allotropes in different physical phases; for example,phosphorushasnumerous solid allotropes,which all revert to the same P4form when melted to the liquid state.
History
[edit]The concept of allotropy was originally proposed in 1840 by the Swedish scientist BaronJöns Jakob Berzelius(1779–1848).[2][3]The term is derived fromGreekάλλοτροπἱα(allotropia)'variability, changeableness'.[4]After the acceptance ofAvogadro's hypothesisin 1860, it was understood that elements could exist as polyatomic molecules, and two allotropes of oxygen were recognized as O2and O3.[3]In the early 20th century, it was recognized that other cases such as carbon were due to differences in crystal structure.
By 1912,Ostwaldnoted that the allotropy of elements is just a special case of the phenomenon ofpolymorphismknown for compounds, and proposed that the terms allotrope and allotropy be abandoned and replaced by polymorph and polymorphism.[5][3]Although many other chemists have repeated this advice,IUPACand most chemistry texts still favour the usage of allotrope and allotropy for elements only.[6]
Differences in properties of an element's allotropes
[edit]Allotropes are different structural forms of the same element and can exhibit quite different physical properties and chemical behaviours. The change between allotropic forms is triggered by the same forces that affect other structures, i.e.,pressure,light,andtemperature.Therefore, the stability of the particular allotropes depends on particular conditions. For instance,ironchanges from abody-centered cubicstructure (ferrite) to aface-centered cubicstructure (austenite) above 906 °C, andtinundergoes a modification known astin pestfrom ametallicform to asemimetallicform below 13.2 °C (55.8 °F). As an example of allotropes having different chemical behaviour, ozone (O3) is a much stronger oxidizing agent than dioxygen (O2).
List of allotropes
[edit]Typically, elements capable of variablecoordination numberand/oroxidation statestend to exhibit greater numbers of allotropic forms. Another contributing factor is the ability of an element tocatenate.
Examples of allotropes include:
Non-metals
[edit]Element | Allotropes |
---|---|
Carbon |
|
Nitrogen |
|
Phosphorus |
|
Oxygen |
|
Sulfur |
|
Selenium |
|
Spin isomers of hydrogen |
|
Metalloids
[edit]Element | Allotropes |
---|---|
Boron |
|
Silicon |
|
Germanium |
|
Arsenic |
|
Antimony |
|
Tellurium |
|
Metals
[edit]Among the metallic elements that occur in nature in significant quantities (56 up to U, without Tc and Pm), almost half (27) are allotropic at ambient pressure: Li, Be, Na, Ca, Ti, Mn, Fe, Co, Sr, Y, Zr, Sn, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Yb, Hf, Tl, Th, Pa and U. Somephase transitionsbetween allotropic forms of technologically relevant metals are those of Ti at 882 °C, Fe at 912 °C and 1394 °C, Co at 422 °C, Zr at 863 °C, Sn at 13 °C and U at 668 °C and 776 °C.
Element | Phase name(s) | Space group | Pearson symbol | Structure type | Description |
---|---|---|---|---|---|
Lithium | α-Li | R3m | hR9 | α-Sm | Forms below 70 K.[9] |
β-Li | Im3m | cI2 | W | Stable at room temperature and pressure. | |
Fm3m | cF4 | Cu | Forms above 7GPa | ||
R3m | hR1 | α-Hg | An intermediate phase formed ~40GPa.[10] | ||
I43d | cI16 | Forms above 40GPa.[10] | |||
oC88 | Forms between 60 and 70 GPa.[11] | ||||
oC40 | Forms between 70 and 95 GPa.[11] | ||||
oC24 | Forms above 95 GPa.[11] | ||||
Beryllium | α-Be | P63/mmc | hP2 | Mg | Stable at room temperature and pressure. |
β-Be | Im3m | cI2 | W | Forms above 1255 °C. | |
Sodium | α-Na | R3m | hR9 | α-Sm | Forms below 20 K. |
β-Na | Im3m | cI2 | W | Stable at room temperature and pressure. | |
Fm3m | cF4 | Cu | Forms at room temperature above 65 GPa.[12] | ||
I43d | cI16 | Forms at room temperature, 108GPa.[13] | |||
Pnma | oP8 | MnP | Forms at room temperature, 119GPa.[14] | ||
tI19* | A host-guest structure that forms above between 125 and 180 GPa.[11] | ||||
hP4 | Forms above 180 GPa.[11] | ||||
Magnesium | P63/mmc | hP2 | Mg | Stable at room temperature and pressure. | |
Im3m | cI2 | W | Forms above 50 GPa.[15] | ||
Aluminium | α-Al | Fm3m | cF4 | Cu | Stable at room temperature and pressure. |
β-Al | P63/mmc | hP2 | Mg | Forms above 20.5 GPa. | |
Potassium | Im3m | cI2 | W | Stable at room temperature and pressure. | |
Fm3m | cF4 | Cu | Forms above 11.7 GPa.[11] | ||
I4/mcm | tI19* | A host-guest structure that forms at about 20 GPa.[11] | |||
P63/mmc | hP4 | NiAs | Forms above 25 GPa.[11] | ||
Pnma | oP8 | MnP | Forms above 58GPa.[11] | ||
I41/amd | tI4 | Forms above 112 GPa.[11] | |||
Cmca | oC16 | Formas above 112 GPa.[11] | |||
Iron | α-Fe,ferrite | Im3m | cI2 | Body-centered cubic | Stable at room temperature and pressure.Ferromagneticat T<770 °C,paramagneticfrom T=770–912 °C. |
γ-iron,austenite | Fm3m | cF4 | Face-centered cubic | Stable from 912 to 1,394 °C. | |
δ-iron | Im3m | cI2 | Body-centered cubic | Stable from 1,394 – 1,538 °C, same structure as α-Fe. | |
ε-iron,Hexaferrum | P63/mmc | hP2 | Hexagonal close-packed | Stable at high pressures. | |
Cobalt[16] | α-Cobalt | hexagonal-close packed | Forms below 450 °C. | ||
β-Cobalt | face centered cubic | Forms above 450 °C. | |||
ε-Cobalt | P4132 | primitive cubic | Forms from thermal decomposition of [Co2CO8]. Nanoallotrope. | ||
Rubidium | α-Rb | Im3m | cI2 | W | Stable at room temperature and pressure. |
cF4 | Forms above 7 GPa.[11] | ||||
oC52 | Forms above 13 GPa.[11] | ||||
tI19* | Forms above 17 GPa.[11] | ||||
tI4 | Forms above 20 GPa.[11] | ||||
oC16 | Forms above 48 GPa.[11] | ||||
Tin | α-tin,gray tin,tin pest | Fd3m | cF8 | d-C | Stable below 13.2 °C. |
β-tin,white tin | I41/amd | tI4 | β-Sn | Stable at room temperature and pressure. | |
γ-tin, rhombic tin | I4/mmm | tI2 | In | Forms above 10 GPa.[17] | |
γ'-Sn | Immm | oI2 | MoPt2 | Forms above 30 GPa.[17] | |
σ-Sn, γ "-Sn | Im3m | cI2 | W | Forms above 41 GPa.[17]Forms at very high pressure.[18] | |
δ-Sn | P63/mmc | hP2 | Mg | Forms above 157 GPa.[17] | |
Stanene | |||||
Polonium | α-Polonium | simple cubic | |||
β-Polonium | rhombohedral |
Most stable structure under standard conditions.
Structures stable below room temperature.
Structures stable above room temperature.
Structures stable above atmospheric pressure.
Lanthanides and actinides
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/0/0a/Actinide_phases.svg/250px-Actinide_phases.svg.png)
- Cerium,samarium,dysprosiumandytterbiumhave three allotropes.
- Praseodymium,neodymium,gadoliniumandterbiumhave two allotropes.
- Plutoniumhas six distinct solid allotropes under "normal" pressures. Their densities vary within a ratio of some 4:3, which vastly complicates all kinds of work with the metal (particularly casting, machining, and storage). A seventh plutonium allotrope exists at very high pressures. Thetransuraniummetals Np, Am, and Cm are also allotropic.
- Promethium,americium,berkeliumandcaliforniumhave three allotropes each.[19]
Nanoallotropes
[edit]In 2017, the concept of nanoallotropy was proposed.[20]Nanoallotropes, or allotropes ofnanomaterials,are nanoporous materials that have the same chemical composition (e.g., Au), but differ in their architecture at the nanoscale (that is, on a scale 10 to 100 times the dimensions of individual atoms).[21]Such nanoallotropes may help create ultra-small electronic devices and find other industrial applications.[21]The different nanoscale architectures translate into different properties, as was demonstrated forsurface-enhanced Raman scatteringperformed on several different nanoallotropes of gold.[20]A two-step method for generating nanoallotropes was also created.[21]
See also
[edit]Notes
[edit]- ^IUPAC,Compendium of Chemical Terminology,2nd ed. (the "Gold Book" ) (1997). Online corrected version: (2006–) "Allotrope".doi:10.1351/goldbook.A00243
- ^See:
- Berzelius, Jac. (1841).Årsberättelse om Framstegen i Fysik och Kemi afgifven den 31 Mars 1840. Första delen[Annual Report on Progress in Physics and Chemistry submitted March 31, 1840. First part.] (in Swedish). Stockholm, Sweden: P.A. Norstedt & Söner. p. 14.From p. 14:"Om det ock passar väl för att uttrycka förhållandet emellan myrsyrad ethyloxid och ättiksyrad methyloxid, så är det icke passande för de olika tillstånd hos de enkla kropparne, hvari dessa blifva af skiljaktiga egenskaper, och torde för dem böra ersättas af en bättre vald benämning, t. ex.Allotropi(afαλλότροπος,som betyder: af olika beskaffenhet) ellerallotropiskt tillstånd."(If it [i.e., the wordisomer] is also well suited to express the relation between formic acid ethyl oxide [i.e., ethyl formate] and acetic acid methyloxide [i.e., methyl acetate], then it [i.e., the wordisomers] is not suitable for different conditions of simple substances, where these [substances] transform to have different properties, and [therefore the wordisomers] should be replaced, in their case, by a better chosen name; for example,Allotropy(fromαλλότροπος,which means: of different nature) orallotropic condition.)
- Republished in German:Berzelius, Jacob; Wöhler, F. (1841)."Jahres-Bericht über die Fortschritte der physischen Wissenschaften"[Annual Report on Progress of the Physical Sciences].Jahres Bericht Über die Fortschritte der Physischen Wissenschaften(in German).20.Tübingen, (Germany): Laupp'schen Buchhandlung: 13.From p. 13:"Wenn es sich auch noch gut eignet, um das Verhältniss zwischen ameisensaurem Äthyloxyd und essigsaurem Methyloxyd auszudrücken, so ist es nicht passend für ungleiche Zustände bei Körpern, in welchen diese verschiedene Eigenschaften annehmen, und dürfte für diese durch eine besser gewählte Benennung zu ersetzen sein, z. B. durchAllotropie(vonαλλότροπος,welches bedeutet: von ungleicher Beschaffenheit), oder durchallotropischen Zustand."(Even if it [i.e., the wordisomer] is still well suited to express the relation between ethyl formate and methyl acetate, then it is not appropriate for the distinct conditions in the case of substances where these [substances] assume different properties, and for these, [the wordisomer] may be replaced with a better chosen designation, e.g., withAllotropy(fromαλλότροπος,which means: of distinct character), or withallotropic condition.)
- Merriam-Webster online dictionary:Allotropy
- ^abcJensen, W. B.(2006), "The Origin of the Term Allotrope",J. Chem. Educ.,83(6): 838–39,Bibcode:2006JChEd..83..838J,doi:10.1021/ed083p838.
- ^"allotropy",A New English Dictionary on Historical Principles,vol. 1, Oxford University Press, 1888, p. 238.
- ^Ostwald, Wilhelm; Taylor, W.W. (1912).Outlines of General Chemistry(3rd ed.). London, England: Macmillan and Co., Ltd. p. 104.From p. 104: "Substances are known which exist not only in two, but even in three, four or five different solid forms; no limitation to the number is known to exist. Such substances are called polymorphous. The name allotropy is commonly employed in the same connexion, especially when the substance is an element. There is no real reason for making this distinction, and it is preferable to allow the second less common name to die out."
- ^Jensen 2006, citing Addison, W. E. The Allotropy of the Elements (Elsevier 1964) that many have repeated this advice.
- ^Werner Heisenberg – FactsNobelprize.org
- ^Raj, G.Advanced Inorganic Chemistry Vol-1.Krishna Prakashan. p. 1327.ISBN9788187224037.RetrievedJanuary 6,2017.
- ^Overhauser, A. W. (1984-07-02). "Crystal Structure of Lithium at 4.2 K".Physical Review Letters.53(1). American Physical Society (APS): 64–65.Bibcode:1984PhRvL..53...64O.doi:10.1103/physrevlett.53.64.ISSN0031-9007.
- ^abHanfland, M.; Syassen, K.; Christensen, N. E.; Novikov, D. L. (2000). "New high-pressure phases of lithium".Nature.408(6809). Springer Science and Business Media LLC: 174–178.Bibcode:2000Natur.408..174H.doi:10.1038/35041515.ISSN0028-0836.PMID11089965.S2CID4303422.
- ^abcdefghijklmnopDegtyareva, V.F. (2014). "Potassium under pressure: Electronic origin of complex structures".Solid State Sciences.36:62–72.arXiv:1310.4718.Bibcode:2014SSSci..36...62D.doi:10.1016/j.solidstatesciences.2014.07.008.
- ^Hanfland, M.; Loa, I.; Syassen, K. (2002-05-13). "Sodium under pressure: bcc to fcc structural transition and pressure-volume relation to 100 GPa".Physical Review B.65(18). American Physical Society (APS): 184109.Bibcode:2002PhRvB..65r4109H.doi:10.1103/physrevb.65.184109.ISSN0163-1829.
- ^McMahon, M. I.; Gregoryanz, E.; Lundegaard, L. F.; Loa, I.; Guillaume, C.; Nelmes, R. J.; Kleppe, A. K.; Amboage, M.; Wilhelm, H.; Jephcoat, A. P. (2007-10-18)."Structure of sodium above 100 GPa by single-crystal x-ray diffraction".Proceedings of the National Academy of Sciences.104(44): 17297–17299.Bibcode:2007PNAS..10417297M.doi:10.1073/pnas.0709309104.ISSN0027-8424.PMC2077250.PMID17947379.
- ^Gregoryanz, E.; Lundegaard, L. F.; McMahon, M. I.; Guillaume, C.; Nelmes, R. J.; Mezouar, M. (2008-05-23). "Structural Diversity of Sodium".Science.320(5879). American Association for the Advancement of Science (AAAS): 1054–1057.Bibcode:2008Sci...320.1054G.doi:10.1126/science.1155715.ISSN0036-8075.PMID18497293.S2CID29596632.
- ^Olijnyk, H.; Holzapfel, W. B. (1985-04-01). "High-pressure structural phase transition in Mg".Physical Review B.31(7). American Physical Society (APS): 4682–4683.Bibcode:1985PhRvB..31.4682O.doi:10.1103/physrevb.31.4682.ISSN0163-1829.PMID9936412.
- ^de la Peña O’Shea, Víctor Antonio; Moreira, Iberio de P. R.; Roldán, Alberto; Illas, Francesc (8 July 2010). "Electronic and magnetic structure of bulk cobalt: The α, β, and ε-phases from density functional theory calculations".The Journal of Chemical Physics.133(2): 024701.doi:10.1063/1.3458691.PMID20632764.
- ^abcdDeffrennes, Guillaume; Faure, Philippe; Bottin, François; Joubert, Jean-Marc; Oudot, Benoit (2022). "Tin (Sn) at high pressure: Review, X-ray diffraction, DFT calculations, and Gibbs energy modeling".Journal of Alloys and Compounds.919:165675.arXiv:2203.16240.doi:10.1016/j.jallcom.2022.165675.
- ^Molodets, A. M.; Nabatov, S. S. (2000). "Thermodynamic Potentials, Diagram of State, and Phase Transitions of Tin on Shock Compression".High Temperature.38(5): 715–721.doi:10.1007/BF02755923.S2CID120417927.
- ^Benedict, U.; Haire, R. G.; Peterson, J. R.; Itie, J. P. (1985). "Delocalisation of 5f electrons in curium metal under high pressure".Journal of Physics F: Metal Physics.15(2): L29–L35.Bibcode:1985JPhF...15L..29B.doi:10.1088/0305-4608/15/2/002.
- ^abUdayabhaskararao, Thumu; Altantzis, Thomas; Houben, Lothar; Coronado-Puchau, Marc; Langer, Judith; Popovitz-Biro, Ronit; Liz-Marzán, Luis M.; Vuković, Lela; Král, Petr (2017-10-27)."Tunable porous nanoallotropes prepared by post-assembly etching of binary nanoparticle superlattices".Science.358(6362): 514–518.Bibcode:2017Sci...358..514U.doi:10.1126/science.aan6046.hdl:10067/1472420151162165141.ISSN0036-8075.PMID29074773.
- ^abc"Materials That Don't Exist in Nature Might Lead to New Fabrication Techniques".israelbds.org.Archived fromthe originalon 2017-12-09.Retrieved2017-12-08.
References
[edit]- Chisholm, Hugh,ed. (1911). .Encyclopædia Britannica(11th ed.). Cambridge University Press.
External links
[edit]![](https://upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png)
- Nigel Bunce and Jim Hunt."The Science Corner: Allotropes".Archived fromthe originalon January 31, 2008.RetrievedJanuary 6,2017.
- Allotropes – Chemistry Encyclopedia