Chapter 3 A property matter
Worksheet 3.3 How can we make the properties of compounds
benefit us?
1
Polymers are sometimes called giant molecules because they contain so many atoms. As polymer chains
are twisted together they form fibres. Diamond and graphite are called giant molecules because they have
many atoms within the structure bonded together. Metals have special properties because they have
delocalised outer electrons.
Complete the table below by sketching the bonding that would be found within each of the substances listed:
Substance
Sketch
Type of
bonding
polyethylene
diamond
covalent
copper
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
2
The most common synthetic polymer is polyethylene. Polyethylene is a polymer formed when ethylene
molecules are joined together end to end. The formulae for ethylene is CH2=CH2. Sometimes this molecule
is called ethene and the polymer formed from it polyethene.
To model the formation of polyethylene, form a line of ten students and ask each student to fold their arms
across their chest – this corresponds to the double bond. Now ask each student to unfold their arms and
join hands with the students on either side of them to from a 10-person chain. This is what happens in a
polymerisation reaction. The double bond between the carbon atoms is broken and only single bonds
remain as the carbons join onto other carbon atoms. In polyethylene there are more than ten units bonded
together. There can be many tens of thousands of CH2=CH2 monomers joined together.
3
a
The chemical reaction for creating polyethylene is called an addition reaction. Each ethylene molecule
adds on to the next ethylene molecule. Write a chemical equation showing how polyethylene is formed
from ethylene in the space below.
b
Describe how jelly jubes and toothpicks could be used to demonstrate the polymerisation of ethylene.
Polyethylene comes in different grades and has different uses depending on how many monomers are
joined together. One grade of polyethylene has about 70 monomers linked together to form a polymer with
waxlike properties. It is used in floor polishes. Another grade is used to make plastic toys. It has about
5 000 monomers linked together. Cross-linked polyethylene is used to make the plastic caps for milk and
soft drink bottles.
What properties would the polythene need to have if it was to be used to make children’s toys?
4
The polymer used to create food wrap is polyethylene. Because it is made from long chains which are
lined up in rows it is transparent and it can be easily stretched to go around food of different shapes.
Explain this behaviour using the analogy of the line of ten students that was formed earlier.
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
5
Freezer bags are made from polyethylene in which the long chains become tangled up. This changes the
properties of the polymer so that it is no longer able to allow the light to pass through it easily and it is more
difficult for molecules of gases or water to pass through the polymer. This keeps the food inside the bag
fresh and prevents it from drying out. Draw a diagram to illustrate how the chains of polyethylene are
arranged in food wrap and how they are arranged differently in freezer bags.
6
What does the term plasticiser mean?
7
Why would it be better to take a tent made from nylon rather than a tent made from canvas on your next
holiday?
8
What is one disadvantage of making tents from plastic?
9
Is nylon a plastic? Explain your answer.
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
10 Different kinds of plastics have different properties. The table below lists some of the useful properties of
different plastics.
Property
Example
Ability to transmit light
Food wrap is transparent
Good insulators of heat
Polystyrene is used to make food coolers as it is a poor
conductor of heat energy and a good insulator.
Good insulators of
electricity
Copper wires are coated with PVC as the polymer is a poor
conductor of electricity.
Hardness
Aeroplane windows are made of perspex as it is very hard
and strong.
Non-stick
The Teflon coating on saucepans stops them from sticking to
food.
Waterproofing
PVC or nylon is used to make rain jackets as it is waterproof.
Resistant to corrosion
None of the plastics will rust.
Ability to be compressed
and then return to its
shape
Latex is used to make a ball because it is compressible and
has a good bounce.
What properties would the ‘plastic’ need if you wanted to make a cover for a mobile phone?
11 Perspex is an addition polymer which has the appearance of glass. It is made from this monomer:
Draw a part of the perspex polymer which contains at least four monomer units. (Hint: remember what
happened to the ethylene when it joined up with other monomers to from polyethylene.)
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
Read the following information and then answer the questions that follow:
Polymers which do not melt when heated but char instead are called thermosetting polymers. These polymers
must be shaped during their manufacture. They are cross-linked, rigid, strong polymers which enables
them to be used for tasks involving high temperatures that would cause thermoplastic polymers to fail. The
cover of a Playstation console is made from a thermosetting plastic, as is the case of a laptop computer.
The highly cross-linked polymer Ebonite was first created in 1851 and it is still used to create bowling balls.
12 What does the term cross-linked mean when referring to plastics?
13 How are thermoplastics different to thermosetting polymers?
14 How would thermoplastics ‘fail’ at high temperatures?
15 What could happen if a laptop computer was made from a thermoplastic polymer?
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
16 Complete the table below to identify whether the listed objects should be made from thermoplastic or
thermosetting polymers and justify your choice. The first one has been done for you.
Object
Thermoplastic polymer
Thermosetting polymer
√
Coffee Cup
The cup needs to hold its
shape when filled with hot
water.
Container for storing
ice cream
Hair dryer
Electric jug
Lunch box
Tray for making ice cubes
Child’s bucket to take to the
beach
17 Use this website to review your knowledge of atoms and ions and covalent and ionic bonding. What type of
bonding is found in polymers?
18 Explore ‘Where are polymers?’ to learn more about how polymers are used to create clothing, footwear,
toys, musical instruments, packaging for food and many other products. Carefully read the section called
‘What’s so great about polymers’ and make a list of the advantages and disadvantages of using synthetic
polymers.
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia
19 This website also has lots of information about how polymers are used in different ways. How were
polymers used in wartime?
20 Not all polymers are man-made. Use this website to find out about natural polymers. Record the names of
four natural polymers and where they are found and/or what they are used for.
21 Now make a virtual polymer at this website. You can make polyethylene or a protein, take your pick!
22 Which one is this?
Oxford Big Ideas Science 3
ISBN 978 0 19 556453 2
© Oxford University Press Australia