Hydrocarbon
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/* General properties */ Revised section
[[Image:Methane-3D-balls.png|thumb|240px|right|A 3-dimensional rendered [[Ball-and-stick model]] of the [[methane]] molecule. Methane is part of a [[homologous series]] known as [[alkanes]], which are forms of hydrocarbons that comprise single [[chemical bond|bonds]].]]
In [[organic chemistry]], a '''hydrocarbon''' is an [[organic compound]] consisting entirely of [[hydrogen]] and [[carbon]]. With relation to chemical terminology, [[aromatic hydrocarbon]]s or arenes, [[alkane]]s, [[alkene]]s and [[alkyne]]-based compounds composed entirely of carbon or hydrogen are referred to as "pure" hydrocarbons, whereas other hydrocarbons with bonded compounds or impurities of sulphur or nitrogen, are referred to as "impure", and remain somewhat erroneously referred to as hydrocarbons.
Hydrocarbons are referred to as consisting of a "backbone" or "skeleton" composed entirely of [[carbon]] and [[hydrogen]] and other bonded compounds, and lack a [[functional group]] that generally facilitates [[combustion]].
The majority of hydrocarbons found naturally occur in [[crude oil]], where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can [[catenation|catenate]] to form seemingly limitless chains.<ref>Clayden, J., Greeves, N., et al. (2000), p21</ref><ref>McMurry, J. (2000), p75-81</ref>
==Types of hydrocarbons ==
The classifications for hydrocarbons defined by [[IUPAC nomenclature of organic chemistry]] are as follows:
# '''Saturated hydrocarbons''' ([[alkanes]]) are the most simple of the hydrocarbon species and are composed entirely of single bonds and are saturated with hydrogen; they are the basis of petroleum fuels and are either found as linear or branched species of unlimited number. The general formula for saturated hydrocarbons is C<sub>''n''</sub>H<sub>''2n+2''</sub> (assuming non-cyclic structures).
#[[Unsaturated hydrocarbon]]s have one or more double or triple bonds between carbon atoms. Those with one double bond are called [[alkene]]s, with the formula C<sub>''n''</sub>H<sub>''2n''</sub> (assuming non-cyclic structures). Those containing triple bonds are called [[alkyne]]s, with general formula C<sub>''n''</sub>H<sub>''2n-2''</sub>.
#[[Cycloalkanes]] are hydrocarbons containing one or more carbon rings to which hydrogen atoms are attached. The general formula for a saturated hydrocarbon containing one ring is C<sub>''n''</sub>H<sub>''2n''</sub>
#[[Aromatic hydrocarbon]]s, also known as [[arene]]s, are hydrocarbons that have at least one [[aromatic ring]].
Hydrocarbons can be [[gases]] (e.g. [[methane]] and [[propane]]), [[liquids]] (e.g. [[hexane]] and [[benzene]]), waxes or low melting [[solids]] (e.g. [[paraffin wax]] and [[naphthalene]]) or [[polymers]] (e.g. [[polyethylene]], [[polypropylene]] and [[polystyrene]]).
=== General properties ===
Because of differences in molecular structure, the empirical formula remains different between hydrocarbons; in linear, or "straight-run" alkanes, alkenes and alkynes, the amount of bonded hydrogen lessens in alkenes and alkynes due to the "self-bonding" or catenation of carbon preventing entire saturation of the hydrocarbon by the formation of double or triple bonds.
This inherent ability of hydrocarbons to bond to themselves is referred to as [[catenation]], and allows hydrocarbon to form more complex molecules, such as [[cyclohexane]], and in rarer cases, arenes such as [[benzene]]. This ability comes from the fact that bond character between carbon atoms is entirely non-polar, in that the distribution of electrons between the two elements is somewhat even due to the same electronegativity values of the elements (~0.30), and does not result in the formation of an electrophile.
Generally, with catenation comes the loss of the total amount of bonded hydrocarbons and an increase in the amount of energy required for bond cleavage due to strain exerted upon the molecule; in molecules such as cyclohexane, this is referred to as [[ring strain]], and occurs due to the "destabilized" spatial electron configuration of the atom.
In simple chemistry, as per [[valence bond theory]], the carbon atom must follow the "''4-hydrogen rule''", which states that the maximum number of atoms available to bond with carbon is equal to the number of electrons that are attracted into the outer shell of carbon. In terms of shells, carbon consists of an incomplete outer shell, which comprises 4 electrons, and thus has 4 electrons available for covalent or dative bonding.
According to thermodynamics studies, hydrocarbons are stable in great depths within the earth. Hydrocarbons also are abundant in the universe. On [[Titan (moon)|Titan]], Saturn's largest moon, there are lakes and seas filled with liquid methane and ethane, confirmed by the Cassini-Huygens Mission.{{Fact|date=March 2008}}
=== Simple hydrocarbons and their variations ===
<center>
{| class="wikitable" align="center"
!Number of<br />carbon atoms
![[Alkane]]
![[Alkene]]
![[Alkyne]]
![[Cycloalkane]]
![[Alkadiene]]
|- align=center
| 1 ||[[Methane]] ||— ||— ||— ||—
|- align=center
| 2 ||[[Ethane]] ||[[Ethene]] ||[[Acetylene|Ethyne]] || — || —
|- align=center
| 3 ||[[Propane]] ||[[Propene]] ||[[Methylacetylene|Propyne]] || [[Cyclopropane]] || [[Allene]]
|- align=center
| 4 ||[[Butane]]<br>[[Isobutane]] ||[[Butene]] ||[[Butyne]] || [[Cyclobutane]]<br>[[Methylcyclopropane]] || [[Butadiene]]
|- align=center
| 5 ||[[Pentane]]<br>[[Isopentane]]<br>[[Neopentane]] ||[[Pentene]] ||[[Pentyne]] || [[Cyclopentane]] || [[Pentadiene]]<br>[[Isoprene]]
|- align=center
| 6 ||[[Hexane]] ||[[Hexene]] ||[[Hexyne]] || [[Cyclohexane]] || [[Hexadiene]]
|- align=center
| 7 ||[[Heptane]] ||[[Heptene]] ||[[Heptyne]] || [[Cycloheptane]]<br>[[Methylcyclohexane]] || [[Heptadiene]]
|- align=center
| 8 ||[[Octane]] ||[[Octene]] ||[[Octyne]] || [[Cyclooctane]] || [[Octadiene]]
|- align=center
| 9 ||[[Nonane]] ||[[Nonene]] ||[[Nonyne]] || [[Cyclononane]] || [[Nonadiene]]
|- align=center
| 10 ||[[Decane]] ||[[Decene]] ||[[Decyne]] || [[Cyclodecane]] || [[Decadiene]]
|}
</center>
==Usage==
Hydrocarbons are one of the Earth's most important [[energy resource]]s. The predominant use of hydrocarbons is as a combustible [[fuel]] source.
Mixtures of volatile hydrocarbons are now used in preference to the [[chlorofluorocarbons]] as a [[propellant]] for [[aerosol spray]]s, due to chlorofluorocarbons impact on the [[ozone layer]].
[[Methane]] [1C] and [[ethane]] [2C] are gaseous at ambient temperatures and cannot be readily liquified by pressure alone. [[Propane]] [3C] is however easily liquified, and exists in 'propane bottles' mostly as a liquid. [[Butane]] [4C] is so easily liquified that it safely provides a safe, volatile fuel for small pocket lighters. [[Pentane]] [5C] is a clear liquid at room temperature, commonly used in chemistry and industry as a powerful nearly odorless [[solvent]] of waxes and high molecular weight organic compounds, including greases. [[Hexane]] [6C] is also a widely used non-polar, non-aromatic solvent, as well as a significant fraction of common [[gasoline]].
The [6C] through [10C] alkanes, alkenes and isomeric cycloalkanes are the top components of [[gasoline]], [[naptha]], [[jet fuel]] and specialized industrial solvent mixtures. With the progressive addition of carbon units, the simple non-ring structured hydrocarbons have higher viscosities, lubricating indices, boiling points, solidification temperatures, and deeper color. At the opposite extreme from [1C] methane lie the heavy tars that remain as the ''lowest fraction'' in a crude oil refining retort. They are collected and widely utilized as roofing compounds, pavement composition, wood preservatives (the [[creosote]] series) and as extremely high viscosity sheer-resisting liquids.
=== Burning hydrocarbons ===
{{mainarticle|Combustion}}
Hydrocarbons are currently the main source of the world’s [[electric power|electric energy]] and heat sources (such as home heating) because of the energy produced when burnt. Often this energy is used directly as heat such as in home heaters, which use either [[oil]] or [[natural gas]]. The hydrocarbon is burnt and the heat is used to heat water, which is then circulated. A similar principle is used to create electric energy in power plants.
As methane only releases one carbon dioxide for two water molecules, it is considered the cleanest fuel.{{Fact|date=February 2008}}
==== Petroleum ====
{{main|Petroleum}}
[[Image:ShellMartinez-refi.jpg|thumb|right|340px|[[Oil refinery|Oil refineries]] are key to obtaining hydrocarbons; [[crude oil]] is processed through several stages to form desirable hydrocarbons, used in fuel and other commercial products.]]
Liquid geologically-extracted hydrocarbons are referred to as [[petroleum]] (literally "rock oil") or [[mineral oil]], while gaseous geologic hydrocarbons are referred to as [[natural gas]]. All are significant sources of fuel and raw materials as a feedstock for the production of [[organic chemistry|organic chemicals]] and are commonly found in the Earth's subsurface using the tools of [[petroleum geology]].
The extraction of liquid hydrocarbon fuel from a number of [[sedimentary basin]]s has been integral to modern [[energy development]]. Hydrocarbons are [[mining|mined]] from [[tar sands]], [[oil shale]] and potentially extracted from sedimentary [[methane hydrate]]s. These reserves require distillation and upgrading to produce [[synthetic crude]] and petroleum.
[[Oil reserves]] in sedimentary rocks are the principal source of hydrocarbons for the energy, [[transport]] and [[petrochemical]] industries. Hydrocarbons are of prime economic importance because they encompass the constituents of the major [[fossil fuel]]s ([[coal]], petroleum, [[natural gas]], etc.) and [[plastic]]s, [[paraffin]], [[wax]]es, [[solvent]]s and oils. In urban [[pollution]], these components--along with NOx and [[sunlight]]--all contribute to the formation of [[tropospheric ozone]].
== See also ==
{{wiktionary}}
*[[Abiogenic petroleum origin|Abiogenic petroleum origin hypothesis]]
*[[Biohydrocarbon]]
*[[Energy storage]]
*[[Fractional distillation]]
*[[Functional group]]
*[[Hydrocarbon mixtures]]
== Notes ==
<references />
== References ==
# McMurry, J. (2000). ''Organic Chemistry'' 5<sup>th</sup> ed. Brooks/Cole: Thomson Learning.
# Clayden, J., Greeves, N., et al. (2000) ''Organic Chemistry'' Oxford.
{{Refimprove|date=September 2007}}
== External links ==
* [http://www.worldofmolecules.com/fuels/methane.htm The Methane Molecule]
* [http://www.poten.com/ut_glossary.asp Poten & Partners: Glossary of Hydrocarbon Terms]
{{Hydrocarbons}}
[[Category:Soil contamination]]
[[Category:Hydrocarbons|*]]
[[Category:Fossil fuels]]
[[Category:Petroleum]]
[[Category:Oilfield terminology]]
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