Chemistry
Polymer structures Learning objectives: • identify polymers from diagrams showing their bonding and structure • explain why some polymers can stretch • explain why some plastics do not soften on heating.
KEY WORDS intermolecular force monomer polymer repeating unit
Polymers such as poly(ethene), PVC, PTFE and nylon are used in many areas of everyday life. These polymers are very large molecules. They are made in different ways and have different properties. Can we link their properties to their structure as chemicals?
Polymers Polymers are very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds and so form a chain. strong covalent bonds
Figure 2.25 Model of polymers such as polyvinyl chloride H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
strong covalent bonds
Figure 2.26 The bonds between the atoms in a polymer chain are strong covalent bonds.
The forces between polymer molecules are weaker. These forces can be broken so the polymer chains can move over each other so the polymer can be stretched, but are not so weak that the chains pull apart. There are many forces between two long polymer chains and so the substances are solids at room temperature. 1
weaker forces between polymer chains
Figure 2.27 Strong bonds join atoms into a polymer chain. Weaker forces between the chains hold the chain together.
Poly(ethene) is a solid at room temperature not a liquid. Suggest why.
Intermolecular forces
KEY INFORMATION
Chains of polymers are held together to make a bulk substance.
Remember intramolecular bonds are bonds joining atoms within a molecule. Intermolecular forces are forces between chains of molecules.
• The atoms of the monomers along the chains in a polymer are held together by strong covalent bonds. These are bonds within the polymer molecules and so are intramolecular bonds. • The chains of the polymer are held together by weak forces of attraction. These are forces between polymer molecules and so are intermolecular forces.
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AQA GCSE Chemistry for Combined Science: Trilogy: Student Book
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