Giant covalent molecules

• What type of bonding leads to the formation of substances with different structures?

  Covalent bonding
• What are the two types of structures formed by covalent bonding?

  • Small molecules: fixed number of atoms joined by covalent bonds
  • Giant covalent substances: many atoms joined by covalent bonds
• What is silicon dioxide commonly called?

  Silica
• What is the main compound found in sand?

  Silicon dioxide
• How are the atoms in silicon dioxide linked together?

  By strong covalent bonds
• What type of structure does silicon dioxide have?

  A giant covalent structure
• Do giant covalent structures have a set number of atoms joined together?

  No, there is no set number of atoms
• Why do substances with giant covalent structures have high melting and boiling points?

  Because large amounts of energy are needed to overcome their strong covalent bonds
• What state are substances with giant covalent structures typically in at room temperature?

  Solids
• Why can't most substances with giant covalent structures conduct electricity?

  They have no charged particles that are free to move
• Which form of carbon can conduct electricity?

  Graphite
• What are the differences between diamond and graphite in terms of structure and bonding?

  • Diamond:
  • Each carbon atom is joined to four others
  • Forms a tetrahedral network structure
  • No free electrons
  • Graphite:
  • Each carbon atom forms three covalent bonds
  • Forms layers of hexagonal rings
  • Has delocalised electrons
• What makes diamond very hard and useful for cutting tools?

  The rigid network of carbon atoms held by strong covalent bonds
• Does diamond conduct electricity?

  No, it does not conduct electricity
• How do the layers in graphite interact with each other?

  There are no covalent bonds between the layers
• What allows graphite to conduct electricity?

  The presence of delocalised electrons that can move between layers
• What makes graphite useful as a lubricant?

  The weak forces between the layers allow them to slide over each other
• What are graphene and fullerenes in relation to carbon structures?

  • Graphene: A single layer of graphite with strong covalent bonds
  • Fullerenes: Molecules of carbon atoms with hollow shapes based on hexagonal rings
• What properties does graphene have due to its structure?

  Very high melting point, strong, and conducts electricity well
• What is the first fullerene to be discovered?

  Buckminsterfullerene
• What is the molecular structure of buckminsterfullerene?

  Made up of 60 carbon atoms joined by strong covalent bonds
• Why does buckminsterfullerene have a low melting point?

  Because there are weak intermolecular forces between its molecules
• What is a nanotube?

  A layer of graphene rolled into a cylinder
• What are the properties of nanotubes?

  High tensile strength and can conduct electricity due to delocalised electrons
• What are the applications of nanotubes?

  • Useful in nanotechnology
  • Useful in electronics
  • Useful in specialized materials
• What type of molecules do polymers have?

  Very large molecules
• How are atoms in a polymer molecule joined together?

  By strong covalent bonds in long chains
• What is an example of a polymer?

  Poly(ethene)
• What are the properties of polymers compared to small molecules?

  • Stronger intermolecular forces than small molecules
  • Melt at higher temperatures
  • Solids at room temperature