GCSE Chemistry revision

Polymers

How bonding and structure are related to the properties of substances

AQA 4.2.2.5 Foundation & Higher

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Polymers are large molecules made up of many smaller repeating units called monomers joined together in a long chain.
Polypropylene is a common example of a polymer found in plastics, formed from propene monomers with the formula C₃H₆.
A single polymer molecule can be thousands of atoms long, making it a giant molecular structure.

1. What Are Polymers? AQA

Polymers are large molecules made up of many smaller repeating units called monomers joined together in a long chain.
Polypropylene is a common example of a polymer found in plastics, formed from propene monomers with the formula C₃H₆.
A single polymer molecule can be thousands of atoms long, making it a giant molecular structure.

You can identify a polymer by spotting a small section of the molecule that repeats along the chain.
The repeating unit is drawn inside curved brackets with bonds shown passing through the brackets on each side.
The letter n is written in the bottom right corner of the brackets to represent the number of repeating units in the polymer chain.
Instead of drawing out hundreds of monomers, you can represent the whole polymer by drawing just the repeating unit with n (or a specific number) in the corner.

2. Identifying the Repeating Unit AQA

You can identify a polymer by spotting a small section of the molecule that repeats along the chain.
The repeating unit is drawn inside curved brackets with bonds shown passing through the brackets on each side.
The letter n is written in the bottom right corner of the brackets to represent the number of repeating units in the polymer chain.
Instead of drawing out hundreds of monomers, you can represent the whole polymer by drawing just the repeating unit with n (or a specific number) in the corner.

The atoms within a polymer chain are held together by strong covalent bonds, which require very high temperatures to break.
The forces between separate polymer molecules are intermolecular forces, which are much weaker than covalent or ionic bonds.
Because polymer chains are very long, they have a large surface area, meaning there are many intermolecular forces acting between molecules.

3. Bonding Within Polymers AQA

The atoms within a polymer chain are held together by strong covalent bonds, which require very high temperatures to break.
The forces between separate polymer molecules are intermolecular forces, which are much weaker than covalent or ionic bonds.
Because polymer chains are very long, they have a large surface area, meaning there are many intermolecular forces acting between molecules.

To melt or boil a polymer, you need to break the intermolecular forces between molecules, not the covalent bonds within them.
Although intermolecular forces are individually weak, the sheer number of them in long polymer chains means a significant amount of energy is still needed to overcome them.
Polymers have lower melting points than giant covalent structures (e.g. diamond) or giant ionic structures (e.g. sodium chloride), but higher melting points than simple molecular substances like oxygen or chlorine.
The relatively high number of intermolecular forces explains why polymers are generally solid at room temperature.

4. Melting Points & Physical State AQA

To melt or boil a polymer, you need to break the intermolecular forces between molecules, not the covalent bonds within them.
Although intermolecular forces are individually weak, the sheer number of them in long polymer chains means a significant amount of energy is still needed to overcome them.
Polymers have lower melting points than giant covalent structures (e.g. diamond) or giant ionic structures (e.g. sodium chloride), but higher melting points than simple molecular substances like oxygen or chlorine.
The relatively high number of intermolecular forces explains why polymers are generally solid at room temperature.

Two major categories of polymers are addition polymers and condensation polymers, each formed by different types of reactions.
Addition polymers, such as polypropylene, are formed when monomers containing a double bond join together without any other product being made.