Plastics

All of the Organic Chemistry that we have worked through so far has been done to give us a deeper understanding of a common chemical in our everyday lives - plastic.

This video gives a good overview of the history of plastics:

Plastics are an amazing technology, but their use has led to soooooo many problems. What is the future of plastics? How can we continue to use plastics without creating such a big waste issue for our planet?

There is a variety of plastic used in our everyday life:

The main advantage of plastics are their ability to be recycled...but this isn't the case for every plastic (for example, polystyrene). Also, recycling is expensive, and we do not do it as often as we should. That has led to a new movement - REFUSE single-use plastics.

Over the next two weeks, we will be looking at the past, present and future of one plastic - polythene (also called PE, polyethene and polyethylene).

• How was it discovered?
• How is it made?
• How is it used? Why?
• How has its production changed over time? Why?
• How has its use changed over time? Why?
• What is the future for polythene?

Polymerisation

Polymer = macro-molecule (huge molecule) made up of many repeating units
Monomer = the starting molecule for a polymer (mono = "one"; mer = "unit")
Repeating Unit = the basic structural component of the polymer; the part that is repeated continually in the structure of the polymer
Addition Polymerisation = polymerisation where the monomers are simply added together when the double (or triple) bond of neighbouring monomers contribute one electron each to the formation of a new bond.

Addition Polymerisation

CASE STUDY #1: Polyvinyl Chloride (PVC)

CASE STUDY #2: Polyacetylene

Identifying the Monomer

Drawing Alkenes

When given the name of an alkene, we need to be able to draw them. For this assessment, it is useful to draw them around the C=C double bond, as this is where polymerisation occurs. This video goes through how you draw an alkene from its name.

1. It has "ene" in the name, so draw a C=C double bond, and four bonds (2 off each carbon atom)
2. Use the number in the alkene part of name to number the far-left carbon atom
3. Use the prefix (but-, pent-, hex- etc.) to build the rest of the carbon chain. Number every carbon.
4. If it says cis, make sure the carbon chain is all on the same side of the C=C bond (above it or below it on the page. If it says trans, make sure the carbon chain goes across the C=C bond, like in the picture and video.
5. Add any side chains to the appropriate carbon(s) - you had already numbered the carbon atoms so this should be easy :)
6. Fill in all of the hydrogen atoms to the vacant bonds.

Alkenes - Geometric Isomerism

Because the C=C double bond cannot freely rotate in space, alkenes have a special type of isomerism, called geometric isomerism (or cis/trans isomerism).

Alkenes - Functional Group and Structural Isomerism

Our second hydrocarbon homologous series are the alkenes. They are unsaturated carbons, containing a carbon-carbon double bond.

In this first part, we need to be able to:

• identify the functional group
• apply the general formula to predict the number of hydrogen atoms
• draw structural isomers
• name structural isomers

Alkanes

Alkanes are our first hydrocarbon homologous series to focus on. They cannot be used to make addition polymers because they are saturated, but an understanding of this group is critical foundation organic chemistry.

Hydrocarbons

Hydrocarbons are, as the name suggests, made up of only hydrogen and carbon atoms. There are three types of hydrocarbons (called homologous series):

1. Alkanes
2. Alkenes
3. Alkynes

You need to know about the naming, structure and properties of these.

It is very worthwhile to come up with your own mnemonic to remember the naming of the first four.