6) Polymers and Giant Covalent Structures

Polymers — Long Chains of Repeating Units

1. Polymers are made of many small units (monomers) linked together to form long chains with repeating sections.

2. In polymers, all atoms are bonded by strong covalent bonds.

3. Instead of drawing the entire polymer, you can draw a repeating unit, which is the smallest section that repeats.

   • Example: Poly(ethene) has a repeating unit of (C₂H₄)n.

     

4. To find the molecular formula of a polymer, write the formula of the repeating unit inside brackets, followed by 'n' outside.

   • For poly(ethene), the molecular formula is (C₂H₄)ₙ.

5. The intermolecular forces between polymer molecules are stronger than in simple covalent molecules, so more energy is required to break them.

   • This means that polymers are solid at room temperature.

6. However, the intermolecular forces in polymers are weaker than ionic or giant covalent bonds, so they have lower boiling points than ionic or giant molecular compounds.

Giant Covalent Structures (Macromolecules)

1. In giant covalent structures, all atoms are bonded together by strong covalent bonds, forming a macromolecule.

2. These structures have very high melting and boiling points due to the large amount of energy needed to break the covalent bonds between atoms.

3. Giant covalent structures do not contain charged particles, so they do not conduct electricity, not even when molten (except graphite).

4. Examples of giant covalent structures include:

   • Diamond: Each carbon atom forms four covalent bonds in a rigid, giant structure.

   • Graphite: Each carbon atom forms three covalent bonds, creating layers of hexagons. Each carbon atom has one delocalised electron.

   • Silicon Dioxide (SiO₂): Commonly known as silica (found in sand), where each silicon atom bonds with oxygen atoms to form a giant structure.