Allotrope: Difference between revisions
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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 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. | ||
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]]. | ||
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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. | 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. | ||
[[Category:Chemistry Workgroup]] | |||
Revision as of 12:18, 1 December 2007
Allotropes are different forms of a particular chemical element, resulting from different configurations of atoms 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.
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 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.