Polymers are very large molecules which are made by linking many smaller, identical molecules known as monomers. These monomers are joined together by strong covalent bonds.
One well-known example of a polymer is poly(ethene).
In this example of polyethene, four ethene molecules join to form a poly(ethene) chain. However, in reality, poly(ethene) molecules can contain thousands of these monomers in a chain.
Due to the numerous atoms and covalent bonds in a polymer molecule, it’s often easier to represent them using repeating units. For example, the diagram below shows the repeating unit of poly(ethene).
One key property of polymers is the presence of strong intermolecular forces. These forces exist between polymer molecules, which are notably strong due to the large size of the molecules. Because of these strong forces, it takes a lot of energy to break the bonds between the polymer molecules. As a result, polymers often have high melting and boiling points and are typically solids at room temperature.
In comparison, smaller molecules have weaker intermolecular forces, which makes them easier to break apart. This results in lower melting and boiling points, and smaller molecules are often liquids or gases at room temperature.