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Allotropes are different forms of a particular chemical [[element]], resulting from different configurations of [[atom]]s  making up the molecular or crystalline structure. The existence of an element in more than one form is known as allotropy, but allotropy does not extend to include forms of an element that arise purely because of a change of state, so that, for example, liquid [[nitrogen]] and gaseous nitrogen do not rank as allotropes of that element.
'''Allotropes''' are different forms of an assemblage of the [[atom]]s of a particular chemical [[element]] in the same physical state (gas, liquid, or solid), the different forms resulting from different configurations of the assemblage making up its molecular or crystalline structure.  
 
The existence of an element in more than one form is known as allotropy.  In accord with the definition of an allotrope, allotropy does not extend to include different forms of an element purely because of a difference of physical state, so that, for example, liquid [[nitrogen]] and gaseous nitrogen do not qualify as allotropes of that element.
   
   
Examples of allotropes are the two well-known forms of [[oxygen]]: dioxygen (''O''<sub>2</sub>), which forms roughly one fifth of the atmosphere, and ozone (''O''<sub>3</sub>), also present in the upper atmosphere but in far smaller amount, which absorbs harmful ultraviolet light from the Sun, and also acts as a [[greenhouse gas]].
Examples of allotropes are the two well-known forms of [[oxygen]]: dioxygen (''O''<sub>2</sub>), which forms roughly one fifth of the atmosphere, and ozone (''O''<sub>3</sub>), also present in the upper atmosphere but in far smaller amount, which absorbs harmful ultraviolet light from the Sun, and also acts as a [[greenhouse gas]].
[[Carbon]] in normal circumstances exists as one of the two allotropes graphite (where the atoms are arranged in hexagonal layers) and diamond (where the atoms form a three-dimensional tetrahedral structure). Of this pair graphite is the more stable, but fortunately at normal temperatures the rate of conversion from diamond to graphite is imperceptibly slow! In the mid-1980s a further family of carbon allotropes known as fullerenes (or "buckyballs") were discovered, leading to the award of the 1996 Nobel Prize in chemistry to Harold Kroto, Robert Curl and Richard Smalley.
   
   
Other elements which exhibit allotropy include tin, which exists in grey nonmetallic and white metallic forms, phosphorus, which has white, red and black forms, and sulfur, with a number of allotropes, including a plastic amorphous form.
[[Carbon]] has more than 40 allotropes, most of them amorphous.<ref name=mcmurry2010>McMurry J, Fay RC. (2010) ''General Chemistry: An Atoms-First Approach''. Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 9780321571632.</ref> Among the crystalline allotropes is graphite (where the atoms are arranged in hexagonal layers) and diamond (where the atoms form a three-dimensional tetrahedral structure). Of this pair graphite is the more stable, but fortunately at normal temperatures the rate of conversion from diamond to graphite is imperceptibly slow! In the mid-1980s a further family of carbon allotropes known as fullerenes (or "buckyballs") were discovered, leading to the award of the 1996 Nobel Prize in chemistry to Harold Kroto, Robert Curl and Richard Smalley.
Other elements which exhibit allotropy include [[tin]], which exists in grey nonmetallic and white metallic forms, [[phosphorus]], which has white, red and black forms, and sulfur, with a number of allotropes, including rhombic, monoclinic, and  plastic amorphous forms.
 
The German chemist [[Eilhard Mitscherlich]] first discovered allotropy, in sulfur.
 
==References==
{{reflist}}
 
==External link==
[http://www.arb.ca.gov/toxics/tac/appendxc.htm Glossary California Air Resources Board]

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Allotropes are different forms of an assemblage of the atoms of a particular chemical element in the same physical state (gas, liquid, or solid), the different forms resulting from different configurations of the assemblage making up its molecular or crystalline structure.

The existence of an element in more than one form is known as allotropy. In accord with the definition of an allotrope, allotropy does not extend to include different forms of an element purely because of a difference of physical state, so that, for example, liquid nitrogen and gaseous nitrogen do not qualify as allotropes of that element.

Examples of allotropes are the two well-known forms of oxygen: dioxygen (O2), which forms roughly one fifth of the atmosphere, and ozone (O3), also present in the upper atmosphere but in far smaller amount, which absorbs harmful ultraviolet light from the Sun, and also acts as a greenhouse gas.

Carbon has more than 40 allotropes, most of them amorphous.[1] Among the crystalline allotropes is graphite (where the atoms are arranged in hexagonal layers) and diamond (where the atoms form a three-dimensional tetrahedral structure). Of this pair graphite is the more stable, but fortunately at normal temperatures the rate of conversion from diamond to graphite is imperceptibly slow! In the mid-1980s a further family of carbon allotropes known as fullerenes (or "buckyballs") were discovered, leading to the award of the 1996 Nobel Prize in chemistry to Harold Kroto, Robert Curl and Richard Smalley.

Other elements which exhibit allotropy include tin, which exists in grey nonmetallic and white metallic forms, phosphorus, which has white, red and black forms, and sulfur, with a number of allotropes, including rhombic, monoclinic, and plastic amorphous forms.

The German chemist Eilhard Mitscherlich first discovered allotropy, in sulfur.

References

  1. McMurry J, Fay RC. (2010) General Chemistry: An Atoms-First Approach. Upper Saddle River, NJ: Pearson Prentice Hall. ISBN 9780321571632.

External link

Glossary California Air Resources Board