Alkenes

Shelby E, Melanie, Irene
 * alkenes**

media type="file" key="Alkenes Block B.m4a" width="264" height="264" what are alkenes? In organic chemistry, an alkene, olefin or olefine (alkenes are called olefins or olefines because they form oily liquids on reaction with chlorine gas) is an unsaturated chemical compound containing at least one carbon-to-carbon double bond. Alkenes are a family of unsaturated hydrocarbons (compounds containing carbon and hydrogen only) that contain one or more double carbon-carbon bonds. Alkenes with just one double C-C bond form an homologous series with the general formula CnH2n. The first few in this series are [|ethene], propene, butene, and pentene. Higher members of the series show [|isomerism] depending on the position of the double bond. For example, butene (C4H8) has two isomers – but-1-ene (C2H5CH:CH2) and but-2-ene (CH3CH:CHCH3). The general formula of alkenes is CnH2n (the n and the 2n are supposed to be subscripts but I can't figure out how to do that). Alkenes are generally very reactive and typical reactions involve the additions of hydrogens or halogens. .

What makes them different from Alkanes? Alkanes, also known as paraffins, are chemical compounds that consist only of the elements carbon (C) and hydrogen (H). The presence of at least one double bond in alkenes means that they react in ways that [|alkanes] cannot do. It allows, for example, alkenes to be distinguished from alkanes using a simple chemical test. This test involves the use of [|bromine] water – a dilute solution of bromine which is normally orange-brown in color. Bromine water becomes colorless when shaken with an alkene, through an addition reaction, but is not decolorized by alkanes.

 What do alkenes have to do with polymers? Under pressure and in the presence of a suitable catalyst, small alkenes will join together, by the opening up of their double bonds, to form long chains called [|polymers]. The joining up of many individual alkene units by polymerization results in a variety of much-used and familiar plastics. These include polythene, polypropene, epoxy, polystyrene, and polychloroethene (PV).



Polythene, made from ethene, is very cheap and strong, and is easily molded. It is used to make, for example, plastic bags, bottles, and buckets. Polypropene, made from propene, has strong fibers and a high elasticity. It is used, for example, in the manufacture of crates, ropes, and carpets. Epoxy resins are polymers that can be used as adhesives. Polystyrene, made from styrene, is cheap, easily molded, and can be expanded into insulating forma. Polychloroethene (PVC) is made from [|chloroethene] and used for making wire insulation and records.
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