Monomers and Polymers

Overview

This lesson is Lesson 14 of 20 in Exploring Organic Chemistry Layers. Students build on earlier ideas about organic molecules and bonding by comparing monomers and polymers, then zoom in on alkene monomers and how they form polymers. Students model polymerisation to explain why different monomers produce different polymer properties.

Learning intentions

• WALT compare monomers and polymers using scientific language.
• WALT describe polymer formation from alkene monomers using the idea of addition reactions.
• WALT contrast linear, branched, and cross-linked polymer structures using evidence from simple models.
• WALT use particulate and structural representations to explain how structure affects properties.

Success criteria

• I can define monomers and polymers and give examples.
• I can describe the process by which an alkene monomer becomes part of a polymer chain.
• I can compare and contrast how monomer structure influences polymer structure.
• I can use a particle/structural model to justify a claim about polymer properties.

Curriculum links

• Science learning goal: understanding about chemistry involves using models to explain particle behaviour and chemical reactions.
• Nature of Science: develop and use evidence-based explanations from observations and representations.
• Science capabilities: using scientific language, interpreting and communicating findings, and building conceptual understanding through models.
• Processes: exploring patterns and relationships by comparing monomer–polymer pairs and linking structure to outcomes.

Lesson structure (60 minutes)

1. 0–5 min · Starter prompt. Teacher writes: “Are polymers just ‘bigger molecules’ or are they different in a meaningful way?” Students do a quick free-write (3–4 sentences) and label one example.

2. 5–15 min · Mini-teach: key ideas. Teacher explains monomers vs polymers, then introduces alkene monomers and addition polymerisation at a conceptual level (no heavy mechanism detail). Students copy a two-column summary: Monomer / Polymer and add one example each.

3. 15–25 min · Guided comparison (lab-style stations, no real chemicals). Teacher sets up stations with provided polymer/monomer cards (e.g., ethene→poly(ethene), propene→poly(propene) as simplified examples) and asks students to match pairs and justify using structure cues. Students work in pairs to match cards and record one similarity and one difference for each match.

4. 25–40 min · Modelling alkene polymerisation. Teacher demonstrates a simple chain-building model: start with alkene units (C=C shown on monomer cards), then “link” monomers into a repeating unit to form a polymer chain, explaining that bonds change as the C=C becomes part of the chain. Students build two polymer chains from two different alkene monomers provided on worksheets, labelling the repeating unit on each.

5. 40–50 min · Structure types and properties connection. Teacher shows three polymer structure sketches (linear, branched, cross-linked) and poses: “Which structure is most likely to be stiff, elastic, or brittle, and why?” Students complete a short comparison table linking structure type to likely property trends using their models and reasoning.

6. 50–55 min · Whole-class share. Teacher leads a structured discussion: each group shares one evidence-based claim (from their model) and one question they still have. Students practise using stems: “Our model suggests…” and “This is supported because…”

7. 55–60 min · Exit ticket (formative assessment). Teacher gives a prompt: “Using words and a sketch, explain how an alkene monomer becomes part of a polymer, and state one way monomer structure affects polymer structure.” Students submit on a half-page.

Resources

• Monomer/polymer matching cards (paper or digital projected copies without internet use)
• Alkene monomer strip templates showing C=C and carbon skeletons
• Repeating unit and polymer chain worksheets
• Structure sketches for linear/branched/cross-linked polymer types
• Coloured pens/highlighters for linking steps
• Exit ticket slips (printed)
• Teacher slide/board summary of key terms: monomer, polymer, repeating unit, polymerisation, addition (conceptual)

Assessment

• During stations: teacher circulates using a checklist for correct matching and clear justification language.
• During modelling: quick conference check for whether students correctly identify the repeating unit and describe the alkene “linking” conceptually.
• Exit ticket: assess definitions, polymer formation from alkene monomers, and one structure-to-property link.

Differentiation

• Support: provide sentence starters (“A monomer is…”, “In an alkene polymer, the repeating unit is…”) and partially completed chain frames.
• Support: allow students to use the structure cards as prompts when writing the exit ticket explanation.
• Extension: challenge students to predict the likely effect of introducing a substituted alkene (e.g., methyl side group) on branching and related properties, using only model-based reasoning.
• EAL/SEN: offer bilingual glossary on paper if needed and encourage diagrams as a parallel to written explanations; keep explanations short and structured with stems.