Difference between revisions of "Allotropy"

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'''Allotropy''' is a phenomenon in chemistry whereby a given [[chemical element]] can exist in several different structural forms.<ref>{{GoldBookRef|title=allotropes|file=A00243|accessdate=2010-04-05}}.</ref> Each of these forms is called an '''allotrope'''. The best known example is that of [[diamond]] and [[graphite]], which are both allotropes of [[carbon]]. Allotropy can be seen as a special case of [[polymorphism]].
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{| class="wikitable" style="text-align:center; width:30em; float:right; margin:0 0 0 0.5em;"
 
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The term was first proposed by [[Jöns Jakob Berzelius]] in 1841:<ref>{{citation | last = Jensen | first = W. B. | title = The Origin of the Term Allotrope | journal = J. Chem. Educ. | year = 2006 | volume = 83 | issue = 6 | pages = 838–39 | doi = 10.1021/ed083p838}}.</ref> it is derived from the Greek {{Polytonic|άλλοτροπἱα}} (''allotropia''; variation, changeableness), from {{Polytonic|ἄλλος}} (''allos''; other, different) and {{Polytonic|τρόπος}} (''tropos''; turn of mind, manner).<ref>{{Citation | contribution = allotropy | title = A New English Dictionary on Historical Principles | volume = 1 | publisher = Oxford University Press | year = 1888 | page = 238}}.</ref>
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| width=10em | <big>'''C'''</big><br/>[[graphite]]<br/>[[diamond]]<br/>[[Fullerene|[60]fullerene]]<br/>''[[glassy carbon]]''
 
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| width=10em | <big>'''N'''</big>
At any given temperature and pressure, one allotrope will be more thermodynamically stable than the others. Nevertheless, other allotropes can exhibit substantial [[kinetic stability]], e.g. diamond. Allotropy is most pronounced in groups 14, 15 and 16 of the periodic table.
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| width=10em | <big>'''O'''</big><br/>[[dioxygen]]<br/>[[ozone]]
 
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|- valign=top
{| class="wikitable" style="text-align:center;"
 
|-
 
| <big>'''C'''</big>
 
| <big>'''N'''</big>
 
| <big>'''O'''</big>
 
|-
 
 
| <big>'''Si'''</big>
 
| <big>'''Si'''</big>
| <big>'''P'''</big>
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| <big>'''P'''</big><br/>[[black phosphorus]]<br/>[[white phosphorus]]<br/>''[[red phosphorus]]''
| <big>'''S'''</big>
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| <big>'''S'''</big><br/>[[α-sulfur]]<br/>[[β-sulfur]]<br/>[[γ-sulfur]]<br/>[[ε-sulfur]]
|-
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|- valign=top
 
| <big>'''Ge'''</big>
 
| <big>'''Ge'''</big>
| <big>'''As'''</big>
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| <big>'''As'''</big><br/>α-arsenic<br/>yellow arsenic<br/>ε-arsenic<br/>''amorphous arsenic''
| <big>'''Se'''</big>
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| <big>'''Se'''</big><br/>[[α-selenium]]<br/>[[β-selenium]]<br/>[[γ-selenium]]<br/>grey selenium<br/>''red selenium''<br/>''black selenium''
|-
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|- valign=top
| <big>'''Sn'''</big>
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| <big>'''Sn'''</big><br/>[[white tin]]<br/>[[grey tin]]
| <big>'''Sb'''</big>
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| <big>'''Sb'''</big><br/>α-antimony<br/>antimony-I<br/>antimony-II
 
| <big>'''Te'''</big>
 
| <big>'''Te'''</big>
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|- valign=top
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| <big>'''Pb'''</big>
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| <big>'''Bi'''</big><br/>α-bismuth<br/>ζ-bismuth
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| <big>'''Po'''</big><br/>α-polonium<br/>β-polonium
 
|-
 
|-
| <big>'''Pb'''</big>
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| colspan=3 align=left | '''Some allotropes of the elements of groups 14, 15 and 16.''' The most stable allotrope at 25&nbsp;°C and 1&nbsp;bar is listed first; amorphous allotropes are listed in italics.
| <big>'''Bi'''</big>
 
| <big>'''Po'''</big>
 
 
|-
 
|-
 
|}
 
|}
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'''Allotropy''' is a phenomenon in chemistry whereby a given [[chemical element]] can exist in several different structural forms.<ref>{{GoldBookRef|title=allotropes|file=A00243|accessdate=2010-04-05}}.</ref> Each of these forms is called an '''allotrope'''. The best known example is that of [[diamond]] and [[graphite]], which are both allotropes of [[carbon]]. Allotropy can be seen as a special case of [[polymorphism]].
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The term was first proposed by [[Jöns Jakob Berzelius]] in 1841:<ref>{{citation | last = Jensen | first = W. B. | title = The Origin of the Term Allotrope | journal = J. Chem. Educ. | year = 2006 | volume = 83 | issue = 6 | pages = 838–39 | doi = 10.1021/ed083p838}}.</ref> it is derived from the Greek {{Polytonic|άλλοτροπἱα}} (''allotropia''; variation, changeableness), from {{Polytonic|ἄλλος}} (''allos''; other, different) and {{Polytonic|τρόπος}} (''tropos''; turn of mind, manner).<ref>{{OED1st | entry = allotropy | volume = 1 | page = 238}}.</ref>
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At any given temperature and pressure, one allotrope will be more thermodynamically stable than the others. Nevertheless, other allotropes can exhibit substantial [[kinetic stability]], e.g. diamond: such allotropes are said to be metastable.<ref>{{GoldBookRef|title=metastability (of a phase)|file=M03871|accessdate=2010-04-05}}.</ref> Allotropy is most pronounced in groups 14, 15 and 16 of the periodic table. [[Boron]] also forms several allotropes: the different structural forms of the d- and f-block metals are usually referred to as [[phase]]s rather than allotropes.
  
 
==Nomenclature==
 
==Nomenclature==
Most allotropes have long-accepted [[semisystematic name]]s (e.g., [[red phosphorus]], [[white phosphorus]]) or [[trivial name]]s (e.g., [[ozone]], graphite). A systematic nomenclature is available,<ref>{{RedBook2005|pages=49–51}}.</ref> but is not widely used.
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Most allotropes have long-accepted [[semisystematic name]]s (e.g., [[red phosphorus]], [[white phosphorus]]) or [[trivial name]]s (e.g., [[ozone]], graphite). The different allotropes may also be labelled with Greek letters (e.g., α-sulfur, β-sulfur), where the α-allotrope is usually (but not always) the most stable under ambient conditions.
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A systematic nomenclature is available, but is not widely used. Molecular allotropes are named using [[compositional nomenclature]] (e.g., tetraphosphorus for white phosphorus), while solid-state allotropes with infinite structures are labelled withe the [[Pearson symbol]] in parentheses after the element name (e.g., phosphorus(''oS''8) for black phosphorus).<ref>{{RedBook2005|pages=49–51}}.</ref>
  
 
==References==
 
==References==

Latest revision as of 13:17, 23 May 2010

C
graphite
diamond
[60]fullerene
glassy carbon
N O
dioxygen
ozone
Si P
black phosphorus
white phosphorus
red phosphorus
S
α-sulfur
β-sulfur
γ-sulfur
ε-sulfur
Ge As
α-arsenic
yellow arsenic
ε-arsenic
amorphous arsenic
Se
α-selenium
β-selenium
γ-selenium
grey selenium
red selenium
black selenium
Sn
white tin
grey tin
Sb
α-antimony
antimony-I
antimony-II
Te
Pb Bi
α-bismuth
ζ-bismuth
Po
α-polonium
β-polonium
Some allotropes of the elements of groups 14, 15 and 16. The most stable allotrope at 25 °C and 1 bar is listed first; amorphous allotropes are listed in italics.

Allotropy is a phenomenon in chemistry whereby a given chemical element can exist in several different structural forms.[1] Each of these forms is called an allotrope. The best known example is that of diamond and graphite, which are both allotropes of carbon. Allotropy can be seen as a special case of polymorphism.

The term was first proposed by Jöns Jakob Berzelius in 1841:[2] it is derived from the Greek άλλοτροπἱα (allotropia; variation, changeableness), from ἄλλος (allos; other, different) and τρόπος (tropos; turn of mind, manner).[3]

At any given temperature and pressure, one allotrope will be more thermodynamically stable than the others. Nevertheless, other allotropes can exhibit substantial kinetic stability, e.g. diamond: such allotropes are said to be metastable.[4] Allotropy is most pronounced in groups 14, 15 and 16 of the periodic table. Boron also forms several allotropes: the different structural forms of the d- and f-block metals are usually referred to as phases rather than allotropes.

Nomenclature

Most allotropes have long-accepted semisystematic names (e.g., red phosphorus, white phosphorus) or trivial names (e.g., ozone, graphite). The different allotropes may also be labelled with Greek letters (e.g., α-sulfur, β-sulfur), where the α-allotrope is usually (but not always) the most stable under ambient conditions.

A systematic nomenclature is available, but is not widely used. Molecular allotropes are named using compositional nomenclature (e.g., tetraphosphorus for white phosphorus), while solid-state allotropes with infinite structures are labelled withe the Pearson symbol in parentheses after the element name (e.g., phosphorus(oS8) for black phosphorus).[5]

References

  1. allotropes, <http://goldbook.iupac.org/A00243.html> (accessed 5 April 2010), Compendium of Chemical Terminology Internet edition; International Union of Pure and Applied Chemistry (IUPAC).
  2. Jensen, W. B. The Origin of the Term Allotrope. J. Chem. Educ. 2006, 83 (6), 838–39. DOI: 10.1021/ed083p838.
  3. allotropy. In A New English Dictionary on Historical Principles; Oxford University Press, 1888; Vol. 1, p 238.
  4. metastability (of a phase), <http://goldbook.iupac.org/M03871.html> (accessed 5 April 2010), Compendium of Chemical Terminology Internet edition; International Union of Pure and Applied Chemistry (IUPAC).
  5. Nomenclature of Inorganic Chemistry; IUPAC Recommendations 2005; Royal Society of Chemistry: Cambridge, 2005; pp 49–51. ISBN 0-85404-438-8, <http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf>.

External links

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