Unit5EverydayChemicals - The Things we use Everyday Yet...

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– 231 – The Things we use Everyday Yet More Organic Chemistry Before we discuss the chemical makeup of some of the things we use everyday, we are going to have a brief look at the plastic containers that most of this stuff comes in. You might think that these plastics must be really complicated molecules. ....and while they are large molecules, they are actually made up of many repeating units of smaller molecules. These large molecules are what we call polymers , which comes from the Greek, meaning “many parts.” In this section we will consider the types of molecules that can form common polymers and discover how polymers are actually formed. Alkenes These molecules which contain a double bond between two carbon atoms were briefly discussed. The simplest of these molecules is ethylene, C 2 H 4 , which has the following structure: There are many molecules which are based on ethylene, in that they all possess a carbon - carbon double bond (often abbreviated as C=C). All of these molecules can undergo a type of reaction called an addition reaction . In this type of reaction, one of the bonds which makes up the double bond is broken, leaving a carbon - carbon single bond. The electrons which were present in the double bond (one from each carbon atom) are now available to form a bond with some other species. This is the type of reaction that is used when an addition polymer is formed. Each individual molecule that goes into making up the polymer is called a monomer , so a polymer consists of many monomeric units. Many of the plastics that you encounter every day are this type of polymer, and they are all formed by the same type of reaction. H H H H C C
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– 232 – How does the polymerization reaction occur ? (We will look at this in class.) is shown as. ... (recall that a bond consists of 2 electrons, or 2 dots) In the diagrams that follow, the hydrogens have been omitted for more clarity of what’s happening around the carbon atoms. ....but each carbon atom still has 2 hydrogen atoms attached to it. The polymerization process starts with a reaction involving a free radical (has an unpaired electron and is very reactive) catalyst ...shown here as R• , and one ethylene molecule. One of the bonds in the double bond in the ethylene molecule breaks, and the electrons in this bond move to either end of the ethylene molecule. ...this allows the catalyst to attach to the molecule and the whole thing now has an unpaired electron. Another ethylene molecule is encountered by this larger free radical, and the process is repeated. ....over and over again. The process stops when we run out of ethylene. ...the original catalyst is removed and the result is polyethylene, a very long hydrocarbon molecule.
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This note was uploaded on 10/23/2011 for the course CHEMISTRY 1027 taught by Professor Calvin during the Fall '10 term at UWO.

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Unit5EverydayChemicals - The Things we use Everyday Yet...

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