Polymers: giant molecules that stay solid at room temperature

1. A polymer is a material made from very large molecules.
2. Each molecule contains many atoms joined into one long chain.
   1. A short section of the chain, called the repeating unit, is copied over and over to build the whole molecule.
3. Poly(ethene) is a familiar polymer, and part of its chain is written as $-({CH}_2-{CH}_2{)}_n-$.
   1. The subscript $n$ stands for a very large number of repeating units.

Covalent bonds within a chain: strong bonds hold each molecule together

1. Within each polymer molecule, the atoms are joined by strong covalent bonds.
2. A covalent bond is a shared pair of electrons between two atoms.
   1. In poly(ethene) each carbon atom, $C$, is covalently bonded to other carbon atoms and to hydrogen atoms, $H$.
3. These covalent bonds run along the whole length of the chain, linking every atom in the molecule.
4. Because covalent bonds are strong, a great deal of energy is needed to break them.

Intermolecular forces between chains: the reason polymers are solid

1. Separate polymer molecules are attracted to one another by intermolecular forces.
2. These forces act between whole molecules, not within them.
3. Because each molecule is very large, the total attraction between two chains is relatively strong.
   1. The many points of contact along each long chain add up to a large overall attraction.
4. A large amount of energy is needed to overcome these forces so the chains can move past one another.
5. At room temperature there is not enough energy to separate the chains, so polymers are solid.

Reading polymer diagrams: look for long chains of bonded atoms

1. In a diagram, a polymer is drawn as a very long molecule of many atoms joined by lines.
2. Each line between two atoms represents a strong covalent bond.
3. A diagram usually shows only part of the chain, because the full molecule is far too large to draw.
   1. A repeating bracket or a row of dots shows that the pattern continues well beyond the drawn section.
4. If several long chains are drawn side by side, each row is a separate polymer molecule.
5. The spaces between the rows are bridged by intermolecular forces, not by covalent bonds.
6. To explain why a polymer is solid, first state that it is made of very large molecules.
7. Then state that the atoms in each molecule are held by strong covalent bonds.
8. Next explain that the intermolecular forces between the molecules are relatively strong.
9. Finally link this to the property by stating that the polymer is solid at room temperature.
10. Keep the two attractions separate by using within for covalent bonds and between for intermolecular forces.