Lesson video

Hello, I am Mrs. Adcock, and welcome to today's lesson on polymer structures.

We are going to be looking at how polymers are made and some of the properties of polymers.

Today's lesson outcome is I can describe the structure and properties of a polymer.

Some of the keywords that we will be using in today's lesson include polymer, monomer, repeating unit and intermolecular forces.

Here you can see each of those keywords written in a sentence.

It would be a good idea to pause the video now and read through those sentences.

You might like to make some notes so that you can refer back to them later in the lesson if needed.

Today's lesson is split into three parts.

First of all, we are going to look at polymerization.

Then we're going to move on to look at monomer, polymers and repeating unit, and then we're going to move on to look at polymer properties.

Let's get started on the first part of our lesson on polymerization.

Plastics are synthetic polymers and synthetic means these are manmade polymers.

Polymers are long chained molecules that are made from joining together monomers.

Here we can see some examples of polymers that you might be familiar with.

We've got PVC, which stands for polyvinyl chloride, and that's used for insulation, and we can see there it's used for insulating electrical wires.

poly(propene) is a another synthetic polymer and that's used in carpets, and we have poly(ethene), which is commonly known as polythene, and that's used in plastic bags.

Polymers are very large covalent molecules.

Here we can see a section of a polymer chain.

We can see that the backbone of this molecule is carbon atoms that are joined together by covalent bonds.

Polymers are made up of small molecules called monomers.

The prefix, poly, refers to many, and polymers are made from many monomers joined together, and the prefix, mono, means one.

So we have monomers, which are just the single units, and these can join together to form our polymers.

Polymerization is the process of monomers joining together to form polymers.

Time for a check for understanding.

Polymers are made from joining together A, monomers, B, monoxides, C, monatomic, and sometimes you'll see that written as monoatomic.

The correct answer is that polymers are made from joining together monomers.

So monomers are the single unit that we join together in the process of polymerization to form our polymers.

The incorrect answer, B, says monoxides.

An example of a monoxide would be carbon monoxide.

That's carbon joined to one oxygen atom, and monatomic or monoatomic means a single atom.

Alkenes can be used as monomers to make polymers.

The carbon-carbon double bond that we find in alkenes opens up allowing the monomers to join together.

Here are some examples of monomers that can polymerize to form polymers.

We've got two alkenes here, and we can spot that these alkenes, because they both contain that carbon-carbon double bond.

The carbon carbon double bond opens up, and that allows lots of monomers to then join together to form our polymers.

Our monomers can all be represented in different ways.

So you can see here we've got three different images, but these are, but all of these images show the same monomer.

They all show a monomer known as butene and butane has four carbon atoms joined together in a chain, and it also has that carbon-carbon double bond.

The carbon-carbon double bond opens up, and that allows these monomers to join together.

Here we can see we've got lots of monomers, and they've all got that carbon-carbon double bond.

They are all alkenes, and that carbon-carbon double bond opens up and that allows these monomers to bond together with each other forming covalent bonds, and there we've got a section of a polymer chain at the bottom that's been formed from those monomers, we've got the monomer and you can see where the double bond has opened up.

So we've no longer got a double bond in our polymer chain, and we can see where that monomer is within our polymer chain.

Time for another question.

Which of the following monomers can polymerize to form a polymer? Is it A, B, or C? Look carefully at those molecules that you've been given there and decide if they are monomers and whether you'd be able to join them together in polymerization to form a polymer.

The correct answer is A and B, because both A and B contain a carbon-carbon double bond that can open up and join together to form those polymers.

So well done, if you correctly identified A and B.

When naming polymers, we use the word poly followed by the monomer name in brackets.

So for example, the monomer(styrene) can join together to make the polymer polystyrene.

So we've got the word poly, and then in brackets we've put the monomer.

In this case it's styrene.

Here we can see some more examples.

So we've got the monomer, ethene, that will form the polymer poly(ethene).

The monomer chloroethene will form the polymer poly(chloroethene) and the polymer poly(tetrafluoroethene) will be made from the monomer, tetrafluoroethene.

Let's see if we've understood that, poly(propene) is made from which monomer? Is it A, propanol, B, propene, C, propanoic acid? The correct answer is B, propene.

So well done if you got that one correct, we could work this out from the polymer name.

The polymer was called poly(propene), so it's poly, and then the name of the monomer in brackets.

So this will be poly(propene), time for our first practise task of today's lesson, and for this practise task, you need to complete the table below, and to complete the table, you need to pop in the names of the polymers and the monomers that are missing from that table.

Pause the video now have a go at answering this question, then come back when you're ready to go over the answers.

Let's see how you got on.

So the monomer butene will join together to form the polymer poly(butene).

The monomer dichloroethene will form the polymer, poly(dichloroethene).

The polymer poly(styrene) is made from the monomer, styrene.

The polymer, poly(vinyl acetate), is made from the monomer, vinyl acetate.

And the monomer, tetrafluoroethene, makes the polymer, poly(tetrafluoroethene).

Hopefully you got those monomer and polymer names correct.

Well done if you did.

We are now going to move on to the second part of our lesson that's on monomers, polymers and the repeating unit.

Chemical equations for polymerization reactions show the monomer and the polymer.

Here we can see an example of a polymerization reaction.

We've got n number of the monomer, and these join together to form the polymer.

N represents any number, and there are often hundreds of thousands of monomers in a polymer chain.

So we can see we have n number of that monomer, and we then have an arrow, and then we have our polymer.

When we draw our polymer, we've removed the double bond, because this opened up when the monomers joined together, and we have bonds that are sticking out of the sides of square brackets,, and then we put the n on the outside of the square bracket.

The unit that repeats in a polymer is known as the repeating unit.

Here we can see a section of a polymer chain, and here we've got one repeat unit.

So this is the section that is repeating throughout the polymer chain.

Here is an example showing the structures of a monomer, polymer, and the repeating unit.

We've got a monomer with our carbon-carbon double bond.

We've got the polymer and we've got our square bracket with an n on the outside to show that we've got n number of the monomer within that polymer, and then we've got the repeating unit.

You will notice that the structure of the polymer is the repeating unit with square brackets and an n on the outside.

The repeating unit contains open bonds, and these show it is bonded to further repeating units.

Here we can see the open bonds on the ends of our repeating unit.

Time for another question.

Which of the following represents a polymer? Is it A, B, or C? So see if you can think which one might be the monomer, which one is a repeating unit, and which one as the question says is the polymer? The correct answer is B.

B shows a polymer structure, A shows the monomer, and C shows the repeating unit.

So remember, the polymer will have square brackets around it and also have an n on the outside of the brackets.

Here's another question for us to have a go at.

Which of the following shows a monomer? Is it A, B, or C? The correct answer is A.

So well done, if you chose A, A has got the carbon-carbon double bond.

That is a monomer.

Hopefully you notice that B is a polymer stretcher and C is the repeating unit.

Here we have a question, draw the polymer produced from this monomer.

So I will have a go first, and then it'll be your turn to have a go.

First of all, we are going to open up the double bond to show the repeating unit, so we take our monomer, and open up the double bond.

So we've done that at the bottom there.

You can see the double bond is opened up, and now we've got open bonds on either side of our repeating unit.

We are then going to add brackets and an n to indicate the number of repeat units that are present in the polymer.

And now we've drawn our polymer structure from the monomer.

You'll turn to have a go, draw the polymer produced from this monomer.

Pause the video now, and have a go at answering that question.

Hopefully you have produced this polymer here where you've opened up the double bond to show the repeat unit.

You've added brackets and an n to indicate the number of repeat units in the polymer.

Well done if you got that one correct.

We're now going to do the opposite, and we are going to try and draw the monomer that's produced when we've been given the polymer.

So here is a section of a polymer, and we need to draw the monomer.

So what we are going to do, first of all, is identify the repeating unit.

Then we are going to reform the carbon-carbon double bond that will be present in our monomer.

There you can see at the bottom that we've reformed the carbon-carbon double bond.

We've made sure that each of our carbon atoms is only forming four covalent bonds and we have now drawn our monomer.

You'll turn to have a go, draw the monomer that produces this polymer.

Let's see how you got on.

The monomer should look like this.

We identified the repeating unit, then we reformed the carbon-carbon double bond and just made sure that our carbon atoms were each only forming four covalent bonds.

Well done if you got that one correct.

Time for us to have a go at our second practise task of today's lesson.

And you need to complete the table for this task.

So in that first row, you need to fill in the repeat unit, and then in the second row, you've been given the repeat unit, and you need to identify the monomer and the polymer structure.

For the second part of this task, you've got another table to complete.

So you've been given a different polymer structure here, and in the second row you've been given a monomer structure and you need to fill in the missing sections showing the monomer structure, the polymer structure, and the repeat unit.

Let's see how you got up in the first row, we needed to draw the repeat unit.

Now you can use the polymer structure for this and just remove the brackets and the n and your repeat unit should look like that one there.

In the second row, we've been given the repeat unit, and we need to draw the monomer.

So to do this, we need to reform that carbon-carbon double bond, and also draw the polymer.

And to draw the polymer, you need to add square brackets, and an n to the repeat unit.

Hopefully you got those two correct.

Let's have a look at question two.

Question two.

In the first row, you were given the polymer structure, and you needed to draw the monomer, so we need to reform that carbon-carbon double bond and the repeat unit will look just like the polymer, but we need to remove those square brackets and the n.

In the second row, to draw the polymer stretcher, you should have opened up that carbon-carbon double bond.

You should have open bonds on either side of your repeat unit, and then because it's the polymer stretcher, we should have square brackets and an n, and here is the image of the repeat unit for that polymer.

Well done if you were able to identify the monomer stretchers, the polymer stretchers, and the repeat unit for those molecules that you were given, we have looked at the process of polymerization and hopefully you've been able to identify monomers and polymers and the repeating unit when you've been given different stretches.

We're now going to move on to the final part of our lesson looking at polymer properties.

Polymers are very large molecules made up of strong covalent bonds, but they are not giant covalent structures.

Here we can see a polymer, and this is a large covalent molecule.

They are molecules where the atoms are bonded together by covalent bonds.

Here is diamond.

Diamond is not a polymer.

Diamond is a giant covalent structure.

Remember that polymers are large molecules that are made from monomers, so they do contain covalent bonds, but they are not giant covalent structures.

Polymer molecules are strong.

They are held together by relatively strong intermolecular forces.

Here in this image we can see three polymer chains and they are held together by intermolecular forces.

Polymers are solid at room temperature,, and the reason they are solid at room temperature is they need a lot of energy to overcome the intermolecular forces between the polymer molecules, because these polymer chains are so long, there are lots of intermolecular forces, and therefore we need a lot of energy to overcome these intermolecular forces, and that's why polymers are solid at room temperature.

When polymers mount, it is the intermolecular forces that are overcome.

And remember, the covalent bonds are not broken.

Polymers have a higher melting point compared to simple covalent molecules.

Here in the image, we can see a model showing our polymer chains, and they are held together by many intermolecular forces.

Here we've got an example showing simple covalent molecules, and they are held together by fewer intermolecular forces.

Because polymers have got many more intermolecular forces, they need more energy to overcome the relatively stronger intermolecular forces that hold the chains together.

Time for a question.

Can you identify the polymer from these three images shown? Is the polymer shown in A, B, or C? The correct answer is B.

A shows graphite.

That is a giant covalent structure, and remember that polymers are not giant covalent structures.

C shows a molecule of chlorine, and chlorine is a simple covalent molecule.

We can tell B is a polymer, because we've got the repeating unit and we've got square brackets with an n on the outside.

Well done if you correctly identified B as the polymer.

Time for our final practise task of today's lesson.

For this task, you need to first of all describe how atoms are held together in polymer molecules, and what holds the polymer molecules together.

For question two, you need to explain why poly(ethene) is solid at room temperature, but chlorine is a gas at room temperature.

Pause the video now.

Have a go answering these two questions.

Then when you come back, we'll go over the answers.

Let's see how you got on with these two questions.

First of all, we needed to describe how atoms are held together in polymer molecules, and then what holds the polymer molecules together.

The atoms in a polymer molecule are held together by strong covalent bonds, and the polymer molecules are held together by intermolecular forces.

Explain why poly(ethene) is a solid at room temperature, but chlorine is a gas.

Poly(ethene) has a higher melting point than chlorine.

Why does it have a higher melting point? It requires more energy to break the intermolecular forces in poly(ethene) compared to the energy that's needed to break the intermolecular forces in chlorine.

Hopefully you included lots of those key details in your answer.

Well done if you got those correct.

We've reached the end of today's lesson on polymer structures.

We're just gonna summarise some of the key points from today's lesson.

Polymers are very large covalent molecules, but they are not giant covalent structures.

Polymers can be represented by showing repeated units.

We draw the repeated unit and we add square brackets and put an n on the outside to show the number of repeating units that are present in the polymer.

Polymers are made from repeating an identical section called monomers, and we saw how those monomers can contain a carbon-carbon double bond.

Polymers are solid at room temperature, because the intermolecular forces between polymer molecules are relatively strong.

You have worked really hard in today's lesson, so well done.

I hope that you've enjoyed the lesson, and I hope that you're able to join me for another lesson soon.