9.17C - Polymers and repeating units
Learn how small repeating units form very large polymer molecules, and why a polymer sample has a high average relative molecular mass.
Small units, large molecules
A polymer is a substance made of very large molecules. Its molecules contain small sections of structure joined into a repeating chain: many small units together make one large molecule.
Polymer
A polymer is a substance of high average relative molecular mass made up of small repeating units.
A repeating unit is a short section of the chain that repeats. The units are chemically joined; a collection of separate small molecules is not a polymer just because the whole sample is heavy.
[DIAGRAM: asset_name: polymer_repeating_units: Polymer chain made from small repeating units - diagram 1; asset_slug: 221_9_17c_a_polymer_is_a_substance_of_high_average_relative_molecular_mass_made_up_o_diagram1; file: diagram_assets/221_9_17c_a_polymer_is_a_substance_of_high_average_relative_molecular_mass_made_up_o_diagram1.png; recommended_method: deterministic_drawn; description: Exact monochrome teaching diagram showing a generic polymer substance as several long-chain molecules. One chain has repeated unit blocks with continuation marks, one small repeating unit bracketed and labelled, and a note that different chain lengths mean the substance has an average relative molecular mass. The visual deliberately uses generic units only, with no monomer, C=C bond, named polymer, polymerisation mechanism, properties, recycling or natural-polymer content.]
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