|
[[Berkas:Diamond and graphite.jpg|jmpl|300px|[[Intan]] dan [[grafit]] adalah dua alotrop [[karbon]]: bentuk murni dari unsur yang sama tetapi berbeda dalam struktur.]]
{{base tanpapenerjemahan|d=4|m=01|y=2009|i=14|ket=|kat=no}}
[[Image:Diamond and graphite.jpg|thumb|300px|[[Intan]] dan [[grafit]] adalah dua alotrop [[karbon]]: bentuk murni dari unsur yang sama tapi berbeda dalam struktur.]]
'''Alotropi''' (Gr.atau ''allos'alotropisme''', other,(dari and[[bahasa Yunani]] ''troposallos'', manner)'lainnya', ordan ''tropos'alotropisme', 'tata krama' ) adalah sebuah perilaku yang diperlihatkan oleh beberapa [[unsur kimia]]. Unsur-unsur seperti ini dapat ditemukan dalam dua bentuk atau bisa juga lebih, yang dikenal sebagai '''allotrop''' unsur tersebut. Pada tiap alotrop, [[atom|atom-atom]] unsur tersebut [[ikatan kimia|terikat]] dalam bentuk yang berbeda-beda. Alotrop adalah modifikasi struktural yang berbeda-beda dari sebuah unsur. <ref>Allotrope in ''IUPAC Compendium of Chemical Terminology'', Electronic/ version, http://goldbook.iupac.org/A00243.html. Accessed March 2007.</ref>
Sebagai contoh, unsur [[karbon]] memiliki dua alotrop umum: [[intan]], yang terdiri atas atom karbon yang terikat bersama-sama dalam susunan kisi [[tetrahedral]], dan [[grafit]], yang terdiri atas atom karbon yang terikat dalam lembaran-lembaran kisi [[heksagonal]].
== Referensi ==
<!--
Note that allotropy refers only to different forms of an element within the same phase or [[state of matter]] (i.e. different [[solid]], [[liquid]] or [[gas]] forms) - the changes of state between solid, liquid and gas in themselves are not considered allotropy. For some elements, allotropes have different molecular formulae which can persist in different phases - for example, the two allotropes of [[oxygen]] ([[dioxygen]], O<sub>2</sub> and [[ozone]], O<sub>3</sub>), can both exist in the solid, liquid and gaseous states. Conversely, some elements do not maintain distinct allotropes in different phases: for example [[phosphorus]] has numerous solid allotropes, which all revert to the same P<sub>4</sub> form when melted to the liquid state.
== History ==
The concept of allotropy was originally proposed in 1841 by the Swedish scientist Baron [[Jons Jakob Berzelius]] (1779-1848) who offered no explanation.<ref>Jensen W.B., "The Origin of the Term Allotrope", Journal of Chemical Education, 2006, '''83''', 838-9 </ref> After the acceptance of [[Avogadro's law|Avogadro's hypothesis]] in 1860 it was understood that elements could exist as polyatomic molecules, and the two allotropes of oxygen were recognized as O<sub>2</sub> and O<sub>3</sub>. In the early 20th century it was recognized that other cases such as carbon were due to differences in crystal structure.
By 1912, [[Wilhelm Ostwald|Ostwald]] noted that the allotropy of elements is just a special case of the phenomenon of [[Polymorphism (materials science)|polymorphism]] known for compounds, and proposed that the terms allotrope and allotropy be abandoned and replaced by polymorph and polymorphism. Although many other chemists have repeated this advice, [[IUPAC]] and most chemistry texts still favour the usage of allotrope and allotropy for elements only.
== Differences in properties of an element's allotropes ==
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]], [[photochemistry|light]], and [[temperature]]. Therefore the stability of the particular allotropes depends on particular conditions. For instance, [[iron]] changes from a [[body-centered cubic]] structure [[Ferrite (iron)|(ferrite)]] to a [[face-centered cubic]] structure ([[austenite]]) above 906 °C, and [[tin]] undergoes a transformation known as [[tin pest]] from a [[metallic]] phase to a [[semiconductor]] phase below 13.2 °C.
== List of allotropes ==
Typically, elements capable of variable [[coordination number]] and/or [[oxidation states]] tend to exhibit greater numbers of allotropic forms. Another contributing factor is the ability of an element to [[catenation|catenate]]. Allotropes are typically more noticeable in [[non-metal]]s (excluding the [[halogen]]s and the [[noble gas]]es) and [[metalloid]]s. Nevertheless, [[metal]]s tend to have many allotropes.
Examples of allotropes include:
===Non-metals and metalloids===
{| class="wikitable"
|-
! Element
! Allotropes
|-
|''[[Allotropes of carbon|Carbon]]''
|
* [[diamond]] - an extremely hard, transparent crystal, with the carbon atoms arranged in a tetrahedral lattice. A poor electrical conductor. An excellent thermal conductor.
* [[graphite]] - a soft, black, flaky solid, a moderate electrical conductor. The C atoms are bonded in flat hexagonal lattices, which are then layered in sheets.
* [[amorphous carbon]]
* [[fullerene]]s, including "[[buckyball]]s", such as C<sub>60</sub>, and [[carbon nanotube]]s
|-
|''[[Allotropes of phosphorus|Phosphorus]]'':
|
* White phosphorus - crystalline solid {{chem|P|4}}
* Red phosphorus - polymeric solid
* Scarlet phosphorus
* Violet phosphorus
* Black phosphorus - semiconductor, analogous to graphite
* [[Diphosphorus]]
|-
|''[[Allotropes of oxygen|Oxygen]]'':
|
* [[dioxygen]], O<sub>2</sub> - colorless
* [[ozone]], O<sub>3</sub> - blue
* [[tetraoxygen]], O<sub>4</sub> - [[Metastability|metastable]]
* [[solid oxygen|octaoxygen]], {{chem|O|8}} - red
|-
|''[[Nitrogen#Properties|Nitrogen]]:
|
* [[dinitrogen]]
* [[tetranitrogen]]
* trinitrogen
* two solid forms: one hexagonal close-packed and the other alpha cubic
|-
|''[[Allotropes of sulfur|Sulfur]]'':
|
* Plastic (amorphous) sulfur - polymeric solid
* Rhombic sulfur - large crystals composed of S<sub>8</sub> molecules
* Monoclinic sulfur - fine needle-like crystals
* Other ring molecules such as S<sub>7</sub> and S<sub>12</sub>
|-
|''[[Selenium]]'':
|
* "Red selenium," cyclo-Se<sub>8</sub>
* Gray selenium, polymeric Se
* Black selenium
|-
|''[[Boron]]''
|
* amorphous boron - brown powder
* crystalline boron - black, hard (9.3 on Mohs' scale), and a weak conductor at room temperature.
|-
|''[[Germanium]]''
|
*α-germanium -
*β-germanium - at high pressures
|-
|''[[Silicon]]''
|
* amorphous silicon - brown powder
* [[nanocrystalline silicon ]] - similar to the amorphous silicon
* crystalline silicon - has a metallic luster and a grayish color. Single crystals of crystalline silicon can be grown with a process known as the Czochralski process
|-
|''[[Arsenic]]'':
|
* Yellow arsenic - molecular non-metallic As<sub>4</sub>
* Gray arsenic, polymeric As (metalloid)
* Black arsenic (metalloid) and several similar other ones.
|-
|''[[Antimony]]'':
|
* blue-white antimony - the stable form (metalloid)
* yellow antimony (non-metallic)
* black antimony (non-metallic)
* (a fourth one too)
|}
===Metals===
{{Expand-section|date=January 2008}}
Among the naturally occuring metallic elements (up to U, without Tc and Pm), 28 are allotropic at ambient pressure: Li, Be, Na, Ca, Sr, Ti, Mn, Fe, Co, Sr, Y, Zr, Sn, La, Ce, Pr, Nd, (Pm), Sm, Gd, Tb, Dy, Yb, Hf, Tl, Po, Th, Pa, U.
Considering only the technologically-relevant metals, six metals are allotropic: Ti at 882˚C, Fe at 912 and 1394˚C, Co at 422˚C, Zr at 863˚C, Sn at 13˚C and U at 668 and 776˚C.
''[[Tin#Allotropes|Tin]]''
* grey tin (alpha-tin)
* white tin (beta tin)
* rhombic tin (gamma)
''[[Allotropes of iron|Iron]]''
* [[Ferrite (iron)|ferrite]] (alpha iron) - forms below 770°C (the Curie point, Tc ); the iron becomes magnetic in its alpha form; BCC
* beta - forms below 912°C (BCC)
* gamma - forms below 1394°C; face centred cubic (FCC) crystal structure
* delta - forms from cooling down molten iron below 1538°C; has a body-centred cubic (BCC) crystal structure
====Lanthanides and actinides====
*''[[Cerium#Notable characteristics|Cerium]]'', ''[[Samarium#Notable characteristics|Samarium]]'', ''[[Terbium#Notable characteristics|Terbium]]'',''[[Dysprosium#Notable characteristics|Dysprosium]]'' and ''[[Ytterbium#Notable characteristics|Ytterbium]]'' have three allotropes.
*''[[Praseodymium#Notable characteristics|Praseodymium]]'', ''[[Neodymium#Notable characteristics|Neodymium]]'' , ''[[Gadolinium#Notable characteristics|Gadolinium]]'' and ''[[Terbium#Notable characteristics|Terbium]]'' have two allotropes
*''[[Allotropes of plutonium|Plutonium]]'' 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, which adds further difficulties in exotic applications.{{Fact|date=January 2008}} The transuranien metals Np, Am, and Cm are also allotropic.
*''[[Promethium#Notable characteristics|Promethium]]'', [[Americium]], [[Berkelium]], [[Californium]] have 3 allotropes <ref>http://www.iop.org/EJ/article/0305-4608/15/2/002/jfv15i2pL29.pdf?request-id=AFlRqDDL3BGhbarg2wi7Kg</ref>
[[Image:Actinide phases.png|right|thumb|250px|Phase diagram of the actinide elements.]]
==References==
{{reflist}}
[[Kategori:Kimia anorganik]]
==External links==
* http://www.physics.uoguelph.ca/summer/scor/articles/scor40.htm
[[Category:Allotropy]]
[[Category:Inorganic chemistry]]
-->
{{kimia-stub}}
[[ar:تآصل]]
[[be:Алатропія]]
[[bg:Алотропия]]
[[bs:Alotropske modifikacije]]
[[ca:Al·lotropia]]
[[cs:Alotropie]]
[[cy:Alotrop]]
[[de:Allotropie]]
[[el:Αλλότροπα]]
[[en:Allotropy]]
[[eo:Alotropo]]
[[es:Alotropía]]
[[et:Allotroopia]]
[[eu:Alotropia]]
[[fa:دگرشکلی]]
[[fi:Allotropia]]
[[fr:Allotropie]]
[[gl:Alotropía]]
[[he:אלוטרופיה]]
[[hr:Alotropija]]
[[hu:Allotrópia]]
[[is:Fjölgervi]]
[[it:Allotropia (chimica)]]
[[ja:同素体]]
[[kn:ಭಿನ್ನವರ್ತನೆ]]
[[ko:동소체]]
[[ku:Alotrop]]
[[lv:Alotropija]]
[[mn:Аллотропи]]
[[ms:Alotrop]]
[[nl:Allotropie]]
[[nn:Allotrope former]]
[[no:Allotropi]]
[[pl:Alotropia]]
[[pt:Alotropia]]
[[ru:Аллотропия]]
[[simple:Allotrope]]
[[sk:Alotropia]]
[[sl:Alotropija]]
[[sr:Alotropska modifikacija]]
[[sv:Allotropi]]
[[tr:Allotrop]]
[[uk:Алотропія]]
[[vi:Thù hình]]
[[zh:同素异形体]]
| 