Year 9 Science · Unit 2 · Lesson 16

Polymers and Monomers

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Learning Goals

Warm Up

Because… chain

Fill in the missing steps. Each cause leads to the next effect in the chain. The overall outcome is given, use it as a guide.

Ethene (CH₂=CH₂) has a C=C double bond
→
Each ethene monomer links to the next
→
A long chain of –CH₂–CH₂– repeating units forms
→
The product is polyethylene with very different properties to ethene gas
→

Overall outcome:

Your Turn

Real-world context

Every year, Australians use approximately 3.4 billion plastic bags. About 7% are recycled; the rest go to landfill or leak into the environment. Polyethylene bags can take 20–1,000 years to break down. In 2018, Queensland and South Australia became the last states to ban single-use plastic bags, bringing Australia into line with international efforts to reduce plastic pollution.

(a) Using your knowledge of polymer chemistry, explain why polyethylene bags take so long to break down in the environment.

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(b) Describe one natural polymer that could be used as an alternative to plastic bags. Explain, using polymer science, why this natural polymer might break down faster in the environment.

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Show What You Know

1. Polypropylene (PP) and polyethylene (PE) are both made by addition polymerisation but have different properties. Propylene's monomer has a –CH₃ side group attached to the chain. Predict one way this side group would change the properties of PP compared to PE, and explain why using ideas about chain structure.

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2. Condensation polymerisation produces a byproduct, but addition polymerisation does not. Explain this difference in terms of what happens chemically when the monomers join together.

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Wrap Up

In one sentence, what was the main idea of this lesson?

HSCScience · Year 9 Science · Unit 2 · Lesson 16 · Apply Worksheet