Polymers and giant covalent structures

• What type of bonds do polymers and giant covalent substances have?


  Covalent bonds
• What defines a polymer?


  • Long chains of repeating units
  • Formed by linking small units together
  • Contains strong covalent bonds
• What is the repeating section in a polymer called?

  Repeating unit
• How do you find the molecular formula of a polymer?


  Write the molecular formula of the repeating unit in brackets and put an 'n' outside.
• What is the molecular formula of polyethene?


  (CH₂)_n
• Why are most polymers solid at room temperature?


  Because the intermolecular forces between polymer molecules are larger, requiring more energy to break them.
• How do the boiling points of polymers compare to ionic or giant molecular compounds?


  Polymers generally have lower boiling points than ionic or giant molecular compounds.
• What are the characteristics of giant covalent structures?


  • All atoms are bonded by strong covalent bonds
  • Very high melting and boiling points
  • Do not conduct electricity (except for some like graphite)
• What are the main examples of giant covalent structures?

  Diamond, graphite, and silicon dioxide (silica)
• How many covalent bonds does each carbon atom form in diamond?


  Four covalent bonds
• How does the bonding in graphite differ from that in diamond?


  In graphite, each carbon atom forms three covalent bonds and has one delocalised electron.
• What is silicon dioxide commonly known as?


  Silica
• What is required to melt or boil a giant covalent substance?


  You have to break very strong covalent bonds.
• What is needed to melt or boil a simple molecular substance or a polymer?


  Only the weak intermolecular forces need to be broken.