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 with a fixed number of atoms
  • Giant covalent substances with many atoms
• What is silicon dioxide commonly called?

  Silica
• What type of structure does silicon dioxide have?

  Giant covalent structure
• How are the atoms in silicon dioxide linked together?

  By strong covalent bonds
• What is the arrangement of atoms in silicon dioxide?

  Regular arrangement
• What are the melting and boiling points of substances with giant covalent structures?

  Very high melting and boiling points
• Why do substances with giant covalent structures have high melting and boiling points?

  Large amounts of energy are needed to overcome strong covalent bonds
• What state are most substances with giant covalent structures 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 properties?

  • Diamond:
  • Each carbon atom is joined to four others
  • Forms a tetrahedral network
  • Very hard, high melting point, does not conduct electricity
  • Graphite:
  • Each carbon atom forms three bonds
  • Forms layers of hexagonal rings
  • Conducts electricity, slippery
• What is the structure of diamond?

  A giant covalent structure with a tetrahedral network
• What makes diamond useful for cutting tools?

  Its hardness due to a rigid network of carbon atoms
• What is the melting point of diamond?

  Very high
• What type of structure does graphite have?

  A giant covalent structure
• How do carbon atoms bond in graphite?

  Each carbon atom forms three covalent bonds
• What is the arrangement of carbon atoms in graphite?

  Layers of hexagonal rings
• What is unique about the electrons in graphite?

  There is one non-bonded delocalised electron from each atom
• Why can graphite conduct electricity?

  Because it has delocalised electrons that can move
• 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
  • Very strong, high melting point, conducts electricity
  • Fullerenes:
  • Molecules of carbon with hollow shapes
  • Based on hexagonal rings of carbon atoms
• What is the structure of graphene?

  A single layer of graphite
• What properties make graphene useful in electronics?

  It conducts electricity well due to delocalised electrons
• What are fullerenes made of?

  Molecules of carbon atoms
• What is the shape of buckminsterfullerene molecules?

  Spherical
• What are the intermolecular forces like in buckminsterfullerene?

  Weak intermolecular forces
• Why does buckminsterfullerene have a low melting point?

  Because weak intermolecular forces need little energy to overcome
• What is a nanotube?

  A layer of graphene rolled into a cylinder
• What is the length to diameter ratio of nanotubes?

  High length to diameter ratios
• What properties make nanotubes useful in nanotechnology?

  High tensile strength and ability to conduct electricity
• What are the characteristics of polymers?

  • Very large molecules
  • Atoms joined by strong covalent bonds in long chains
  • Variable numbers of atoms in the chains
• What is an example of a polymer?

  Poly(ethene)
• How do the intermolecular forces between polymer molecules compare to those between small molecules?

  Stronger intermolecular forces
• What is the state of polymers at room temperature?

  Solids
• Why do polymers melt at higher temperatures than small molecules?

  Because of stronger intermolecular forces