Polymers: Polymers have very large molecules.

The idea

Polymers are large molecules made from many small repeating units called monomers joined together by covalent bonds. Because each polymer molecule contains many atoms, it is described as a macromolecule. It is important not to confuse these discrete macromolecules with continuous giant covalent structures like diamond. The atoms within a polymer molecule are held by strong covalent bonds, while separate polymer molecules are held together by intermolecular forces. The large size of polymer molecules means the intermolecular forces between them are stronger than those between small molecules, so polymers are often solid at room temperature. An example is poly(ethene), formed from ethene monomers.

What earns the marks

• Polymers are macromolecules made from many monomers joined together.
• Monomers are small repeating units that covalently bond to form a polymer.
• The atoms within a polymer molecule are held by strong covalent bonds.
• Intermolecular forces act between separate polymer molecules.
• Large polymer molecules have stronger intermolecular forces than small molecules, so many polymers are solid at room temperature.

Common mistakes and how to put them right

• Confusing monomers with polymers.

  Put it right: Monomers are the small repeating units and polymers are the large molecules made from them.

• Thinking polymers are held together only by intermolecular forces.

  Put it right: Covalent bonds hold the atoms within each polymer molecule.

• Assuming all polymers are identical.

  Put it right: Different monomers produce different polymers with different properties.

Exam tips

• Define monomer and polymer clearly before describing polymer structure.
• State that covalent bonds join atoms within a polymer molecule, while intermolecular forces act between molecules.
• Use a named example, such as poly(ethene) from ethene, to show understanding.