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Allotropy
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<h2 id="history">History</h2> <p>The concept of allotropy was originally proposed in 1840 by the Swedish scientist Baron <a href="/facts/J%25C3%25B6ns_Jakob_Berzelius/HakSv3sP">Jöns Jakob Berzelius</a> (1779–1848).<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The term is derived from <a href="/facts/Greek_language/pzDd6eIz">Greek</a> <i> </i>άλλοτροπἱα<i> (allotropia)</i> 'variability, changeableness'.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> After the acceptance of <a href="/facts/Avogadro%2527s_law/r3P987Lj">Avogadro's hypothesis</a> in 1860, it was understood that elements could exist as polyatomic molecules, and two allotropes of oxygen were recognized as O2 and O3.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> In the early 20th century, it was recognized that other cases such as carbon were due to differences in crystal structure. </p><p>By 1912, <a href="/facts/Wilhelm_Ostwald/Abr7Rppg">Ostwald</a> noted that the allotropy of elements is just a special case of the phenomenon of <a href="/facts/Polymorphism_(materials_science)/bu2tqsB9">polymorphism</a> known for compounds, and proposed that the terms allotrope and allotropy be abandoned and replaced by polymorph and polymorphism.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> Although many other chemists have repeated this advice, <a href="/facts/IUPAC/2AV6myCK">IUPAC</a> and most chemistry texts still favour the usage of allotrope and allotropy for elements only.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h2 id="differences-in-properties-of-an-elements-allotropes">Differences in properties of an element's allotropes</h2> <p>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., <a href="/facts/Pressure/eyc37GRG">pressure</a>, <a href="/facts/Photochemistry/GsXNBWon">light</a>, and <a href="/facts/Temperature/QyGe4gmj">temperature</a>. Therefore, the stability of the particular allotropes depends on particular conditions. For instance, <a href="/facts/Iron/QK1JYy8E">iron</a> changes from a <a href="/facts/Body-centered_cubic/92Co7BKM">body-centered cubic</a> structure (<a href="/facts/Allotropes_of_iron/deRQ3dBM">ferrite</a>) to a <a href="/facts/Face-centered_cubic/92Co7BKM">face-centered cubic</a> structure (<a href="/facts/Austenite/Fzp52xYc">austenite</a>) above 906 °C, and <a href="/facts/Tin/obW9mqc3">tin</a> undergoes a modification known as <a href="/facts/Tin_pest/m94dHmJh">tin pest</a> from a <a href="/facts/Metal/PT8hNX6R">metallic</a> form to a <a href="/facts/Semimetal/ELtXVlI5">semimetallic</a> form 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). </p> <h2 id="list-of-allotropes">List of allotropes</h2> <p>Typically, elements capable of variable <a href="/facts/Coordination_number/mf48hsoX">coordination number</a> and/or <a href="/facts/Oxidation_states/W53W6s6V">oxidation states</a> tend to exhibit greater numbers of allotropic forms. Another contributing factor is the ability of an element to <a href="/facts/Catenation/vm7k4zsv">catenate</a>. </p><p>Examples of allotropes include: </p> <h3>Non-metals</h3> <table><tbody><tr><th>Element</th><th>Allotropes</th></tr><tr><td><a href="/facts/Allotropes_of_carbon/GSetCyq6">Carbon</a></td><td><ul><li><a href="/facts/Diamond/IBUdnd1y">Diamond</a> – an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.</li><li><a href="/facts/Lonsdaleite/S5YFqKr5">Lonsdaleite</a> – also called hexagonal diamond.</li><li><a href="/facts/Graphene/QDGUBaPt">Graphene</a> – is the basic structural element of other allotropes, nanotubes, charcoal, and fullerenes.</li><li><a href="/facts/Q-carbon/lAUjjset">Q-carbon</a> – a ferromagnetic, tough, and brilliant crystal structure that is harder and brighter than diamonds.[<i>dubious – discuss</i>]</li><li><a href="/facts/Graphite/sSf3KMXr">Graphite</a> – a semimetallic, soft, black, flaky solid, a good electrical conductor. The C atoms are bonded in flat hexagonal lattices (<a href="/facts/Graphene/QDGUBaPt">graphene</a>), which are then layered in sheets.</li><li><a href="/facts/Linear_acetylenic_carbon/b5ebrE1J">Linear acetylenic carbon</a> (carbyne)</li><li><a href="/facts/Amorphous_carbon/lAUjjset">Amorphous carbon</a></li><li><a href="/facts/Fullerene/LPdnl8ox">Fullerenes</a>, including <a href="/facts/Buckminsterfullerene/F0VebtPK">buckminsterfullerene</a>, also known as "buckyballs", such as C60.</li><li><a href="/facts/Carbon_nanotube/atuDPPaG">Carbon nanotubes</a> – allotropes having a cylindrical nanostructure.</li><li><a href="/facts/Allotropes_of_carbon/GSetCyq6">Schwarzites</a></li><li><a href="/facts/Cyclocarbon/Go19n42Q">Cyclocarbon</a></li><li><a href="/facts/Glassy_carbon/JjH4cQYq">Glassy carbon</a></li><li><a href="/facts/Superdense_carbon_allotropes/DxG87y13">Superdense carbon allotropes</a> – proposed allotropes</li></ul></td></tr><tr><td><a href="/facts/Nitrogen/Nf1QpGDz">Nitrogen</a></td><td><ul><li><a href="/facts/Nitrogen/Nf1QpGDz">Dinitrogen</a> – by far the most common and stable form of nitrogen, found in the air.</li><li><a href="/facts/Hexazine/UoAlXKgD">Hexazine</a></li><li><a href="/facts/Octaazacubane/ndTk3yPF">Octaazacubane</a></li><li><a href="/facts/Tetranitrogen/1Rhl8b0k">Tetranitrogen</a></li><li><a href="/facts/Trinitrogen/FzCUhtrm">Trinitrogen</a></li><li><a href="/facts/Solid_nitrogen/6KF2HYIx">Solid nitrogen</a></li></ul></td></tr><tr><td><a href="/facts/Allotropes_of_phosphorus/GarX3byj">Phosphorus</a></td><td><ul><li><a href="/facts/White_phosphorus/GarX3byj">White phosphorus</a> – crystalline solid of tetraphosphorus (P4) molecules</li><li><a href="/facts/Red_phosphorus/GarX3byj">Red phosphorus</a> – <a href="/facts/Amorphous_solid/YTIzmrR0">amorphous</a> <a href="/facts/Polymer/eF32E50K">polymeric</a> solid</li><li>Scarlet phosphorus</li><li><a href="/facts/Allotropes_of_phosphorus/GarX3byj">Violet phosphorus</a> with <a href="/facts/Monoclinic/5PCwXvzX">monoclinic</a> crystalline structure</li><li><a href="/facts/Allotropes_of_phosphorus/GarX3byj">Black phosphorus</a> – semiconductor, analogous to graphite</li><li><a href="/facts/Diphosphorus/crRKYqB9">Diphosphorus</a> – gaseous form composed of P2 molecules, stable between 1200 °C and 2000 °C; created e.g. by dissociation of P4 molecules of white phosphorus at around 827 °C</li></ul></td></tr><tr><td><a href="/facts/Allotropes_of_oxygen/UVNYnKUQ">Oxygen</a></td><td><ul><li><a href="/facts/Oxygen/acyn6o8r">Dioxygen</a>, O2 – colorless (faint blue liquid and solid)</li><li><a href="/facts/Ozone/o0E5gn2p">Ozone</a>, O3 – blue</li><li><a href="/facts/Tetraoxygen/f8hMAHBQ">Tetraoxygen</a>, O4 – <a href="/facts/Metastability/H72SMWof">metastable</a></li><li><a href="/facts/Octaoxygen/51MyUf1V">Octaoxygen</a>, O8 – red</li></ul></td></tr><tr><td><a href="/facts/Allotropes_of_sulfur/b1TUYVFQ">Sulfur</a></td><td><ul><li>Cyclo-Pentasulfur, Cyclo-S5</li><li>Cyclo-Hexasulfur, Cyclo-S6</li><li>Cyclo-Heptasulfur, Cyclo-S7</li><li>Cyclo-Octasulfur, Cyclo-S8</li></ul></td></tr><tr><td><a href="/facts/Selenium/k975NApC">Selenium</a></td><td><ul><li>"Red selenium", cyclo-Se8</li><li>Gray selenium, polymeric Se</li><li>Black selenium, irregular polymeric rings up to 1000 atoms long</li><li>Monoclinic selenium, dark red transparent crystals</li></ul></td></tr><tr><td><a href="/facts/Spin_isomers_of_hydrogen/zhN4qBMQ">Spin isomers of hydrogen</a></td><td><ul><li>Orthohydrogen, H2 with nuclear spins aligned parallel</li><li>Parahydrogen, H2 with nuclear spins aligned antiparallel</li></ul><p>These nuclear spin isomers have sometimes been described as allotropes, notably by the committee which awarded the 1932 Nobel prize to <a href="/facts/Werner_Heisenberg/n4qzYvj4">Werner Heisenberg</a> for quantum mechanics and singled out the "allotropic forms of hydrogen" as its most notable application.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p></td></tr></tbody></table> <h3>Metalloids</h3> <table><tbody><tr><th>Element</th><th>Allotropes</th></tr><tr><td><a href="/facts/Allotropes_of_boron/fzvC5bye">Boron</a></td><td><ul><li>Amorphous boron – brown powder – B12 regular icosahedra</li><li>α-rhombohedral boron</li><li>β-rhombohedral boron</li><li>γ-orthorhombic boron</li><li>α-tetragonal boron</li><li>β-tetragonal boron</li><li>High-pressure superconducting phase</li></ul></td></tr><tr><td><a href="/facts/Allotropes_of_silicon/fVuCfJVH">Silicon</a></td><td><ul><li><a href="/facts/Amorphous_silicon/lVNN0bv7">Amorphous silicon</a></li><li>α-silicon, a semiconductor, <a href="/facts/Diamond_cubic/6dK7DpGB">diamond cubic</a> structure</li><li>β-silicon - metallic, with the BCC similar to <a href="/facts/Molybdenum/RX6vp2bF">molybdenum</a> and beta-<a href="/facts/Tin/obW9mqc3">tin</a> (High Pressure Phase)</li><li>Q-Silicon - a ferromagnetic (Similar to Q-Carbon) and highly conductive phase of silicon (similar to graphite) <a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></li><li>Silicene, buckled planar single layer Silicon, similar to Graphene</li></ul></td></tr><tr><td><a href="/facts/Germanium/wtoALHGs">Germanium</a></td><td><ul><li>Amorphous germanium</li><li>α-germanium – semimetallic element or semiconductor, with the same structure as diamond (similar chemical properties with sulfur and silicon)</li><li>β-germanium – metallic, with the same structure as beta-tin</li><li>Germanene – Buckled planar Germanium, similar to graphene</li></ul></td></tr><tr><td><a href="/facts/Allotropes_of_arsenic/HFawt6MY">Arsenic</a></td><td><ul><li>Yellow arsenic – molecular non-metallic As4, with the same structure as white phosphorus (Similar chemical properties with nitrogen and phosphorus)</li><li>Gray arsenic, polymeric As (metallic, though heavily anisotropic) (similar to aluminum and antimony in chemical properties)</li><li>Black arsenic – molecular and non-metallic, with the same structure as red phosphorus</li></ul></td></tr><tr><td><a href="/facts/Antimony/YsA7lVgT">Antimony</a></td><td><ul><li>Blue-white antimony – stable form (metallic), with the same structure as gray arsenic (similar to arsenic in chemical properties)</li><li>Black antimony (non-metallic and amorphous, only stable as a thin layer)</li></ul></td></tr><tr><td><a href="/facts/Tellurium/v7QvfIvS">Tellurium</a></td><td><ul><li>Amorphous tellurium – gray-black or brown powder<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></li><li>Crystalline tellurium – hexagonal crystalline structure (metalloid) (similar chemical properties with selenium)</li></ul></td></tr></tbody></table> <h3>Metals</h3> <p>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. Some <a href="/facts/Phase_transition/eLP2BY8R">phase transitions</a> between allotropic forms of technologically relevant metals are those of Ti at 882 °C, Fe at 912 °C and 1,394 °C, Co at 422 °C, Zr at 863 °C, Sn at 13 °C and U at 668 °C and 776 °C. </p> <table><tbody><tr><th>Element</th><th>Phase name(s)</th><th>Space group</th><th><a href="/facts/Pearson_symbol/K3qljnNu">Pearson symbol</a></th><th>Structure type</th><th>Description</th></tr><tr><td rowspan="8"><a href="/facts/Lithium/7vXX6BWA">Lithium</a></td><td>α-Li</td><td>R3m</td><td>hR9</td><td><a href="/facts/Samarium/09K3kl93">α-Sm</a></td><td>Forms below 70 K.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></td></tr><tr><td>β-Li</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td></td><td>Fm3m</td><td>cF4</td><td><a href="/facts/Copper/I8PEE8oX">Cu</a></td><td>Forms above 7GPa</td></tr><tr><td></td><td>R3m</td><td>hR1</td><td><a href="/facts/Mercury_(element)/WlxfoHva">α-Hg</a></td><td>An intermediate phase formed ~40GPa.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a></td></tr><tr><td></td><td>I43d</td><td>cI16</td><td></td><td>Forms above 40GPa.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a></td></tr><tr><td></td><td></td><td>oC88</td><td></td><td>Forms between 60 and 70 GPa.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a></td></tr><tr><td></td><td></td><td>oC40</td><td></td><td>Forms between 70 and 95 GPa.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a></td></tr><tr><td></td><td></td><td>oC24</td><td></td><td>Forms above 95 GPa.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a></td></tr><tr><td rowspan="2"><a href="/facts/Beryllium/dv295voP">Beryllium</a></td><td>α-Be</td><td>P63/mmc</td><td>hP2</td><td><a href="/facts/Magnesium/XyIhd2FG">Mg</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td>β-Be</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Forms above 1255 °C.</td></tr><tr><td rowspan="7"><a href="/facts/Sodium/eYuSPu2V">Sodium</a></td><td>α-Na</td><td>R3m</td><td>hR9</td><td><a href="/facts/Samarium/09K3kl93">α-Sm</a></td><td>Forms below 20 K.</td></tr><tr><td>β-Na</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td></td><td>Fm3m</td><td>cF4</td><td><a href="/facts/Copper/I8PEE8oX">Cu</a></td><td>Forms at room temperature above 65 GPa.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a></td></tr><tr><td></td><td>I43d</td><td>cI16</td><td></td><td>Forms at room temperature, 108GPa.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a></td></tr><tr><td></td><td>Pnma</td><td>oP8</td><td>MnP</td><td>Forms at room temperature, 119GPa.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a></td></tr><tr><td></td><td></td><td>tI19*</td><td></td><td>A host-guest structure that forms above between 125 and 180 GPa.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a></td></tr><tr><td></td><td></td><td>hP4</td><td></td><td>Forms above 180 GPa.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a></td></tr><tr><td rowspan="2"><a href="/facts/Magnesium/XyIhd2FG">Magnesium</a></td><td></td><td>P63/mmc</td><td>hP2</td><td><a href="/facts/Magnesium/XyIhd2FG">Mg</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td></td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Forms above 50 GPa.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a></td></tr><tr><td rowspan="2"><a href="/facts/Aluminium/7wmR8jYE">Aluminium</a></td><td>α-Al</td><td>Fm3m</td><td>cF4</td><td><a href="/facts/Copper/I8PEE8oX">Cu</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td>β-Al</td><td>P63/mmc</td><td>hP2</td><td><a href="/facts/Magnesium/XyIhd2FG">Mg</a></td><td>Forms above 20.5 GPa.</td></tr><tr><td rowspan="7"><a href="/facts/Potassium/FWPwS7Rj">Potassium</a></td><td></td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td></td><td>Fm3m</td><td>cF4</td><td><a href="/facts/Copper/I8PEE8oX">Cu</a></td><td>Forms above 11.7 GPa.<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a></td></tr><tr><td></td><td>I4/mcm</td><td>tI19*</td><td></td><td>A host-guest structure that forms at about 20 GPa.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a></td></tr><tr><td></td><td>P63/mmc</td><td>hP4</td><td><a href="/facts/Nickeline/fbXdeD92">NiAs</a></td><td>Forms above 25 GPa.<a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a></td></tr><tr><td></td><td>Pnma</td><td>oP8</td><td>MnP</td><td>Forms above 58GPa.<a class="footnote-ref" id="fnref:27" href="#fn:27"><sup>27</sup></a></td></tr><tr><td></td><td>I41/amd</td><td>tI4</td><td></td><td>Forms above 112 GPa.<a class="footnote-ref" id="fnref:28" href="#fn:28"><sup>28</sup></a></td></tr><tr><td></td><td>Cmca</td><td>oC16</td><td></td><td>Formas above 112 GPa.<a class="footnote-ref" id="fnref:29" href="#fn:29"><sup>29</sup></a></td></tr><tr><td rowspan="4"><a href="/facts/Allotropes_of_iron/deRQ3dBM">Iron</a></td><td>α-Fe, <a href="/facts/Allotropes_of_iron/deRQ3dBM">ferrite</a></td><td>Im3m</td><td>cI2</td><td><a href="/facts/Body-centered_cubic/92Co7BKM">Body-centered cubic</a></td><td>Stable at room temperature and pressure. <a href="/facts/Ferromagnetism/fH3HFnSl">Ferromagnetic</a> at T<770 °C, <a href="/facts/Paramagnetism/vj1SMbbp">paramagnetic</a> from T=770–912 °C.</td></tr><tr><td>γ-iron, <a href="/facts/Austenite/Fzp52xYc">austenite</a></td><td>Fm3m</td><td>cF4</td><td><a href="/facts/Face-centered_cubic/92Co7BKM">Face-centered cubic</a></td><td>Stable from 912 to 1,394 °C.</td></tr><tr><td>δ-iron</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Body-centered_cubic/92Co7BKM">Body-centered cubic</a></td><td>Stable from 1,394 – 1,538 °C, same structure as α-Fe.</td></tr><tr><td>ε-iron, <a href="/facts/Hexaferrum/SYJqLWzb">Hexaferrum</a></td><td>P63/mmc</td><td>hP2</td><td><a href="/facts/Hexagonal_close-packed/AqL1HUxe">Hexagonal close-packed</a></td><td>Stable at high pressures.</td></tr><tr><td rowspan="3"><a href="/facts/Cobalt/gqhScEw4">Cobalt</a><a class="footnote-ref" id="fnref:30" href="#fn:30"><sup>30</sup></a></td><td>α-Cobalt</td><td></td><td></td><td><a href="/facts/Close-packing_of_equal_spheres/AqL1HUxe">hexagonal-close packed</a></td><td>Forms below 450 °C.</td></tr><tr><td>β-Cobalt</td><td></td><td></td><td><a href="/facts/Close-packing_of_equal_spheres/AqL1HUxe">face centered cubic</a></td><td>Forms above 450 °C.</td></tr><tr><td>ε-Cobalt</td><td>P4132</td><td></td><td><a href="/facts/Cubic_crystal_system/92Co7BKM">primitive cubic</a></td><td>Forms from thermal decomposition of [Co2CO8]. Nanoallotrope.</td></tr><tr><td rowspan="6"><a href="/facts/Rubidium/KDHSe2HM">Rubidium</a></td><td>α-Rb</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Stable at room temperature and pressure.</td></tr><tr><td></td><td></td><td>cF4</td><td></td><td>Forms above 7 GPa.<a class="footnote-ref" id="fnref:31" href="#fn:31"><sup>31</sup></a></td></tr><tr><td></td><td></td><td>oC52</td><td></td><td>Forms above 13 GPa.<a class="footnote-ref" id="fnref:32" href="#fn:32"><sup>32</sup></a></td></tr><tr><td></td><td></td><td>tI19*</td><td></td><td>Forms above 17 GPa.<a class="footnote-ref" id="fnref:33" href="#fn:33"><sup>33</sup></a></td></tr><tr><td></td><td></td><td>tI4</td><td></td><td>Forms above 20 GPa.<a class="footnote-ref" id="fnref:34" href="#fn:34"><sup>34</sup></a></td></tr><tr><td></td><td></td><td>oC16</td><td></td><td>Forms above 48 GPa.<a class="footnote-ref" id="fnref:35" href="#fn:35"><sup>35</sup></a></td></tr><tr><td rowspan="7"><a href="/facts/Tin/obW9mqc3">Tin</a></td><td>α-tin, <a href="/facts/Gray_tin/obW9mqc3">gray tin</a>, <a href="/facts/Tin_pest/m94dHmJh">tin pest</a></td><td>Fd3m</td><td>cF8</td><td><a href="/facts/Diamond_cubic/6dK7DpGB">d-C</a></td><td>Stable below 13.2 °C.</td></tr><tr><td>β-tin, <a href="/facts/White_tin/7nSzQuvj">white tin</a></td><td>I41/amd</td><td>tI4</td><td>β-Sn</td><td>Stable at room temperature and pressure.</td></tr><tr><td>γ-tin, rhombic tin</td><td>I4/mmm</td><td>tI2</td><td><a href="/facts/Indium/zRq3stVb">In</a></td><td>Forms above 10 GPa.<a class="footnote-ref" id="fnref:36" href="#fn:36"><sup>36</sup></a></td></tr><tr><td>γ'-Sn</td><td>Immm</td><td>oI2</td><td>MoPt2</td><td>Forms above 30 GPa.<a class="footnote-ref" id="fnref:37" href="#fn:37"><sup>37</sup></a></td></tr><tr><td>σ-Sn, γ"-Sn</td><td>Im3m</td><td>cI2</td><td><a href="/facts/Tungsten/WYwbNDYX">W</a></td><td>Forms above 41 GPa.<a class="footnote-ref" id="fnref:38" href="#fn:38"><sup>38</sup></a> Forms at very high pressure.<a class="footnote-ref" id="fnref:39" href="#fn:39"><sup>39</sup></a></td></tr><tr><td>δ-Sn</td><td>P63/mmc</td><td>hP2</td><td><a href="/facts/Magnesium/XyIhd2FG">Mg</a></td><td>Forms above 157 GPa.<a class="footnote-ref" id="fnref:40" href="#fn:40"><sup>40</sup></a></td></tr><tr><td><a href="/facts/Stanene/hdg0rh6N">Stanene</a></td><td></td><td></td><td></td></tr><tr><td rowspan="2"><a href="/facts/Polonium/G4rzsyjP">Polonium</a></td><td>α-Polonium</td><td></td><td></td><td><a href="/facts/Cubic_crystal_system/92Co7BKM">simple cubic</a></td><td></td></tr><tr><td>β-Polonium</td><td></td><td></td><td><a href="/facts/Rhombohedral/S7XSr6Yu">rhombohedral</a></td><td></td></tr></tbody></table> <p> Most stable structure under standard conditions. Structures stable below room temperature. Structures stable above room temperature. Structures stable above atmospheric pressure. </p> <h4>Lanthanides and actinides</h4> <ul><li><a href="/facts/Cerium/a7UjMBQ6">Cerium</a>, <a href="/facts/Samarium/09K3kl93">samarium</a>, <a href="/facts/Dysprosium/eMev6zGS">dysprosium</a> and <a href="/facts/Ytterbium/3lerM9uf">ytterbium</a> have three allotropes.</li> <li><a href="/facts/Praseodymium/2lnRJ9dH">Praseodymium</a>, <a href="/facts/Neodymium/GzDkTIoI">neodymium</a>, <a href="/facts/Gadolinium/eLYUeScu">gadolinium</a> and <a href="/facts/Terbium/ICF3PMED">terbium</a> have two allotropes.</li> <li><a href="/facts/Allotropes_of_plutonium/HTlrDzeU">Plutonium</a> has 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. The <a href="/facts/Transuranium_element/a12PwdAw">transuranium</a> metals Np, Am, and Cm are also allotropic.</li> <li><a href="/facts/Promethium/8xvCz9Rg">Promethium</a>, <a href="/facts/Americium/rxL9Yc64">americium</a>, <a href="/facts/Berkelium/ePryEYy3">berkelium</a> and <a href="/facts/Californium/AJVjoVut">californium</a> have three allotropes each.<a class="footnote-ref" id="fnref:41" href="#fn:41"><sup>41</sup></a></li></ul> <h2 id="nanoallotropes">Nanoallotropes</h2> <p>In 2017, the concept of nanoallotropy was proposed.<a class="footnote-ref" id="fnref:42" href="#fn:42"><sup>42</sup></a> Nanoallotropes, or allotropes of <a href="/facts/Nanomaterials/BthrFILJ">nanomaterials</a>, 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).<a class="footnote-ref" id="fnref:43" href="#fn:43"><sup>43</sup></a> Such nanoallotropes may help create ultra-small electronic devices and find other industrial applications.<a class="footnote-ref" id="fnref:44" href="#fn:44"><sup>44</sup></a> The different nanoscale architectures translate into different properties, as was demonstrated for <a href="/facts/Surface-enhanced_Raman_scattering/cgHonFXa">surface-enhanced Raman scattering</a> performed on several different nanoallotropes of gold.<a class="footnote-ref" id="fnref:45" href="#fn:45"><sup>45</sup></a> A two-step method for generating nanoallotropes was also created.<a class="footnote-ref" id="fnref:46" href="#fn:46"><sup>46</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Isomer/PXlvDVdg">Isomer</a></li> <li><a href="/facts/Polymorphism_(materials_science)/bu2tqsB9">Polymorphism (materials science)</a></li></ul> <h2 id="notes">Notes</h2> <ul><li><a href="/facts/Hugh_Chisholm/2vWblUBe">Chisholm, Hugh</a>, ed. (1911). <a href="https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Allotropy">"Allotropy" </a>. <i><a href="/facts/Encyclop%25C3%25A6dia_Britannica_Eleventh_Edition/mPElbCRY">Encyclopædia Britannica</a></i> (11th ed.). Cambridge University Press.</li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Allotropy. <ul><li>Nigel Bunce and Jim Hunt. <a href="https://web.archive.org/web/20080131061355/http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm">"The Science Corner: Allotropes"</a>. Archived from <a href="http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm">the original</a> on January 31, 2008. Retrieved January 6, 2017.</li> <li><a href="http://www.chemistryexplained.com/A-Ar/Allotropes.html">Allotropes – Chemistry Encyclopedia</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "Allotrope". doi:10.1351/goldbook.A00243 <a href="/wiki/International_Union_of_Pure_and_Applied_Chemistry" target="_blank">/wiki/International_Union_of_Pure_and_Applied_Chemistry</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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 (af αλλότροπος, som betyder: af olika beskaffenhet) eller allotropiskt tillstånd." (If it [i.e., the word isomer] 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 word isomers] is not suitable for different conditions of simple substances, where these [substances] transform to have different properties, and [therefore the word isomers] should be replaced, in their case, by a better chosen name; for example, Allotropy (from αλλότροπος, which means: of different nature) or allotropic 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. durch Allotropie (von αλλότροπος, welches bedeutet: von ungleicher Beschaffenheit), oder durch allotropischen Zustand." (Even if it [i.e., the word isomer] 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 word isomer] may be replaced with a better chosen designation, e.g., with Allotropy (from αλλότροπος, which means: of distinct character), or with allotropic condition.) Merriam-Webster online dictionary: Allotropy <a href="https://babel.hathitrust.org/cgi/pt?id=nyp.33433009789326&view=1up&seq=176" target="_blank">https://babel.hathitrust.org/cgi/pt?id=nyp.33433009789326&view=1up&seq=176</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Jensen, W. B. (2006), "The Origin of the Term Allotrope", J. Chem. Educ., 83 (6): 838–39, Bibcode:2006JChEd..83..838J, doi:10.1021/ed083p838. <a href="/wiki/William_B._Jensen" target="_blank">/wiki/William_B._Jensen</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>"allotropy", A New English Dictionary on Historical Principles, vol. 1, Oxford University Press, 1888, p. 238. <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Jensen, W. B. (2006), "The Origin of the Term Allotrope", J. Chem. Educ., 83 (6): 838–39, Bibcode:2006JChEd..83..838J, doi:10.1021/ed083p838. <a href="/wiki/William_B._Jensen" target="_blank">/wiki/William_B._Jensen</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>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." <a href="https://books.google.com/books?id=1w1DAAAAIAAJ&pg=PA104" target="_blank">https://books.google.com/books?id=1w1DAAAAIAAJ&pg=PA104</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Jensen, W. B. (2006), "The Origin of the Term Allotrope", J. Chem. Educ., 83 (6): 838–39, Bibcode:2006JChEd..83..838J, doi:10.1021/ed083p838. <a href="/wiki/William_B._Jensen" target="_blank">/wiki/William_B._Jensen</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Jensen 2006, citing Addison, W. E. 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