AQA · A-Level · Chemistry
Course version: 7405 · Version from Sept 2016
Addition polymers: Addition polymers are unreactive.
Once the double bond has been used up, the chain contains only C–C and C–H bonds.
Checked against the AQA 7405 specification (opens in a new tab) on .
- Point 4 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Once the double bond has been used up, the chain contains only C–C and C–H bonds. These are strong and, because carbon and hydrogen have almost the same electronegativity, essentially non-polar, so there is no δ⁺ carbon for a nucleophile to attack and no δ⁻ site for an electrophile. With no functional group there is nothing for a reagent to grip, which is why poly(ethene) survives acids, alkalis and, importantly, the enzymes of decomposer organisms. That inertness makes polyalkenes useful containers and a disposal problem at the same time. Between chains the only forces are van der Waals forces; each is weak, but over a long chain there are so many contacts that the solid is tough, and longer or straighter chains pack better and melt higher.
What earns the marks
- Saying the chain contains only strong, non-polar C–C and C–H bonds.
- Saying there is no δ⁺ carbon, so nucleophiles are not attracted.
- The consequence that the polymer is not biodegradable and persists in landfill.
- Naming van der Waals forces as the only forces acting between polyalkene chains.
Common mistakes and how to put them right
Saying the chains are held together by strong intermolecular forces, when van der Waals forces are individually weak and merely numerous.
Explaining inertness by the size of the molecule rather than by the absence of a functional group.
Claiming covalent bonds join one chain to the next in an addition polymer.
Naming hydrogen bonding between poly(chloroethene) chains, which have no hydrogen bonded to N, O or F.
Exam tips
- Answer "unreactive" questions in two halves: the bonds are strong, and there is no polar site to attack.
- Name the intermolecular force precisely; "intermolecular forces" alone rarely gains the mark.
- Link non-biodegradability to the same lack of a functional group, since enzymes also need a site to act on.
Try the lesson
The start of the Addition polymers: Addition polymers are unreactive. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement describes the chemical reactivity of addition polymers such as poly(ethene)?
Listen
Once the double bond has been used up, the chain contains only C–C and C–H bonds. These are strong and, because carbon and hydrogen have almost the same electronegativity, essentially non-polar, so there is no δ⁺ carbon for a nucleophile to attack and no δ⁻ site for an electrophile. With no functional group there is nothing for a reagent to grip, which is why poly(ethene) survives acids, alkalis and, importantly, the enzymes of decomposer organisms. That inertness makes polyalkenes useful containers and a disposal problem at the same time. Between chains the only forces are van der Waals forces; each is weak, but over a long chain there are so many contacts that the solid is tough, and longer or straighter chains pack better and melt higher. A strong answer earns marks for these points. saying the chain contains only strong, non-polar C–C and C–H bonds. saying there is no δ⁺ carbon, so nucleophiles are not attracted. the consequence that the polymer is not biodegradable and persists in landfill. naming van der Waals forces as the only forces acting between polyalkene chains. Exam tip: Answer "unreactive" questions in two halves: the bonds are strong, and there is no polar site to attack.
Key words
Say what each word means before you turn the card.
non-polar C–C and C–H bonds
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no functional group
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van der Waals forces
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non-biodegradable
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See every definition
- non-polar C–C and C–H bonds
- Carbon and hydrogen have almost the same electronegativity, so these strong bonds are essentially non-polar.
- no functional group
- There is nothing for a reagent to grip, so the polymer survives acids, alkalis and the enzymes of decomposer organisms.
- van der Waals forces
- These are the only forces between chains; each is weak, but over a long chain there are so many contacts that the solid is tough.
- non-biodegradable
- Because there is no functional group for enzymes to act on, the polymer persists in landfill.
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