Carbon: Difference between revisions
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'''Carbon''' is a [[element|chemical element]] | '''Carbon''' (C) is a [[element|chemical element]]. It is the fourth most abundant element in the Universe,<ref>in the following order: hydrogen (H), helium (He), and oxygen (O) and carbon (C)</ref> and it is literally the building block of life.<ref name=NASACarbCycle>[http://earthobservatory.nasa.gov/Library/CarbonCycle/ The carbon cycle] NASA</ref> | ||
The electron configuration is [He]2s<sup>2</sup>2p<sup>2</sup> | Carbon has an [[atomic number]] ''Z'' = 6, i.e., the carbon nucleus has charge ''6e'', where ''e'' is the [[elementary charge]], and carbon takes the sixth position in the [[periodic table]] of elements. The chemical symbol of carbon is C and its electron configuration is [He]2s<sup>2</sup>2p<sup>2</sup> | ||
One twelfth of the mass | One twelfth of the mass<ref>formerly called atomic weight</ref> of the most abundant [[isotope]] <sup>12</sup>C is by definition the [[unified atomic mass unit]]: A(<sup>12</sup>C) ≡ 1 u. The atomic mass averaged over the naturally occurring isotopes is 12.0107 u. | ||
Carbon has a melting point of 3550 °C (diamond) and a boiling point of 3800 °C (sublimation) | Carbon has a melting point of 3550 °C (diamond) and a boiling point of 3800 °C (sublimation) | ||
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The [[greenhouse gas]] carbon dioxide CO<sub>2</sub> is an oxide of carbon, as is the poisonous gas carbon monoxide (CO). | The [[greenhouse gas]] carbon dioxide CO<sub>2</sub> is an oxide of carbon, as is the poisonous gas carbon monoxide (CO). | ||
==Isotopes== | ==[[Isotope|Isotopes]]== | ||
There are seven isotopes of carbon. | There are seven isotopes of carbon. | ||
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==Forms== | ==Forms== | ||
Carbon occurs naturally in three allotropic forms: graphite, diamond, and fullerines. There is a fourth form, Ceraphite (also known as "white" carbon), which may also exist. | Carbon occurs naturally in three allotropic forms<ref> Allotropic means the existence, especially in the solid state, of two or more crystalline or molecular structural forms of an element. A chemical that exists in more than one form as opposed to different states such as liquid or solid or gas [http://www.arb.ca.gov/toxics/tac/appendxc.htm Glossary] California Air Resources Board</ref>: graphite, diamond, and fullerines. There is a fourth form, Ceraphite (also known as "white" carbon), which may also exist. | ||
Graphite occurs in two forms: alpha<ref> Alpha form occurs in a hexogonal crystal</ref> and beta.<ref>The beta form occurs in rhombohedral crystal </ref> They have identical physical properties and differ only in their crystalline structure. Naturally occurring graphites are reported to contain as much as 30% of the beta form, whereas synthetic materials contain only the alpha form. The alpha type can be converted to the beta by mechanical manipulation, and the beta form will revert to the alpha when it is heated above 1000 °C. | Graphite occurs in two forms: alpha<ref> Alpha form occurs in a hexogonal crystal</ref> and beta.<ref>The beta form occurs in rhombohedral crystal </ref> They have identical physical properties and differ only in their crystalline structure. Naturally occurring graphites are reported to contain as much as 30% of the beta form, whereas synthetic materials contain only the alpha form. The alpha type can be converted to the beta by mechanical manipulation, and the beta form will revert to the alpha when it is heated above 1000 °C. | ||
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==Carbon cycle== | ==Carbon cycle== | ||
Carbon is the essential element of all organic substances ranging from fossil fuels to cell components and DNA. Here on Earth, carbon circulates in various chemical components in a vast biogeochemical cycle through the lithosphere (land and Earth’s interior), hydrosphere (ocean and other bodies of water), and atmosphere. | |||
There are two categories to this global carbon cycle: the geological cycle operating over millions of years, and the biological/physical cycle, which is much shorter and spans a few days to thousands of years.<ref name=NASACarbCycle/> | |||
The oceans of the Earth are dominant environments in the carbon cycle. The oceans collectively hold about 50 times as much carbon as the atmosphere. The carbon in the oceans is exchanged with the atmosphere over a period of hundreds of years. Nearly ½ of all oxygen we breath is generated by photosynthesis of marine plants. Approximately 48% of all carbon produced by burning fossil fuel is sequestered (absorbed) into the oceans. This sequestered carbon accumulates<ref>accumulation of carbon is referred to as a carbon sink or carbon reservoir</ref> in the deep ocean and ocean sediment. <ref>[http://science.hq.nasa.gov/oceans/system/carbon.html The Ocean and the Carbon Cycle] NASA Oceonography</ref> | The oceans of the Earth are dominant environments in the carbon cycle. The oceans collectively hold about 50 times as much carbon as the atmosphere. The carbon in the oceans is exchanged with the atmosphere over a period of hundreds of years. Nearly ½ of all oxygen we breath is generated by photosynthesis of marine plants. Approximately 48% of all carbon produced by burning fossil fuel is sequestered (absorbed) into the oceans. This sequestered carbon accumulates<ref>accumulation of carbon is referred to as a carbon sink or carbon reservoir</ref> in the deep ocean and ocean sediment. <ref>[http://science.hq.nasa.gov/oceans/system/carbon.html The Ocean and the Carbon Cycle] NASA Oceonography</ref> | ||
Revision as of 18:10, 30 November 2007
Carbon (C) is a chemical element. It is the fourth most abundant element in the Universe,[1] and it is literally the building block of life.[2]
Carbon has an atomic number Z = 6, i.e., the carbon nucleus has charge 6e, where e is the elementary charge, and carbon takes the sixth position in the periodic table of elements. The chemical symbol of carbon is C and its electron configuration is [He]2s22p2
One twelfth of the mass[3] of the most abundant isotope 12C is by definition the unified atomic mass unit: A(12C) ≡ 1 u. The atomic mass averaged over the naturally occurring isotopes is 12.0107 u.
Carbon has a melting point of 3550 °C (diamond) and a boiling point of 3800 °C (sublimation)
One of the most widely distributed and abundant of all elements, carbon is a constituent of all organic matter. Diamond, graphite, and fullerenes are non-organic compounds consisting of carbon only; these are known as allotropes of carbon. Most organic carbon compounds contain hydrogen; those that contain oxygen as well include the extensive class of carbohydrates.
Carbon is abundant in the sun, stars, comets, and atmospheres of most planets. Carbon is also found in the form of microscopic diamonds in some meteorites.[4]
Plastics, drugs, animal and plant tissue, foods, textile, wood, paper, and many other common substances contain carbon. Fossil fuels (coal, petroleum, natural gas, etc.) are compounds of carbon.
The greenhouse gas carbon dioxide CO2 is an oxide of carbon, as is the poisonous gas carbon monoxide (CO).
Isotopes
There are seven isotopes of carbon.
12C was adopted as the basis of atomic weights by the International Union of Pure and Applied Chemistry in 1961.[4] 12C Comprises about 98.89% of all carbon on Earth.
13C is another natural, stable isotope of carbon comprising about 1.1% of all natural carbon on Earth.
14C, an unstable isotope with a half-life of 5,715 years, is commonly used to date such materials as wood, archaeological specimens, etc.
Forms
Carbon occurs naturally in three allotropic forms[5]: graphite, diamond, and fullerines. There is a fourth form, Ceraphite (also known as "white" carbon), which may also exist.
Graphite occurs in two forms: alpha[6] and beta.[7] They have identical physical properties and differ only in their crystalline structure. Naturally occurring graphites are reported to contain as much as 30% of the beta form, whereas synthetic materials contain only the alpha form. The alpha type can be converted to the beta by mechanical manipulation, and the beta form will revert to the alpha when it is heated above 1000 °C.
A new allotropic form of carbon was produced in 1969. Ceraphite, white carbon, was produced when pyrolytic graphite was sublimated at low pressures. Under free-vaporization conditions above approximately 2550 °K, "white" carbon will form as small transparent crystals. Little information is presently available about this allotrope.[4]
Carbon cycle
Carbon is the essential element of all organic substances ranging from fossil fuels to cell components and DNA. Here on Earth, carbon circulates in various chemical components in a vast biogeochemical cycle through the lithosphere (land and Earth’s interior), hydrosphere (ocean and other bodies of water), and atmosphere.
There are two categories to this global carbon cycle: the geological cycle operating over millions of years, and the biological/physical cycle, which is much shorter and spans a few days to thousands of years.[2]
The oceans of the Earth are dominant environments in the carbon cycle. The oceans collectively hold about 50 times as much carbon as the atmosphere. The carbon in the oceans is exchanged with the atmosphere over a period of hundreds of years. Nearly ½ of all oxygen we breath is generated by photosynthesis of marine plants. Approximately 48% of all carbon produced by burning fossil fuel is sequestered (absorbed) into the oceans. This sequestered carbon accumulates[8] in the deep ocean and ocean sediment. [9]
Footnotes
- ↑ in the following order: hydrogen (H), helium (He), and oxygen (O) and carbon (C)
- ↑ 2.0 2.1 The carbon cycle NASA
- ↑ formerly called atomic weight
- ↑ 4.0 4.1 4.2 [1] Los Alamos National Labs, Chemistry Division
- ↑ Allotropic means the existence, especially in the solid state, of two or more crystalline or molecular structural forms of an element. A chemical that exists in more than one form as opposed to different states such as liquid or solid or gas Glossary California Air Resources Board
- ↑ Alpha form occurs in a hexogonal crystal
- ↑ The beta form occurs in rhombohedral crystal
- ↑ accumulation of carbon is referred to as a carbon sink or carbon reservoir
- ↑ The Ocean and the Carbon Cycle NASA Oceonography