Chemical bonds and properties-Chemistry

• What are covalent bonds formed between?


  Two non-metal atoms sharing pairs of electrons
• Why are covalent bonds considered strong?


  Because shared electrons are attracted to the nucleus of both atoms
• What types of substances can covalently bonded substances be?


  • Small molecules
  • Large molecules
  • Giant covalent structures
• What are metallic bonds?


  Electrostatic attractions between positive ions and negative delocalised electrons
• Describe the structure of metals.


  • Made of giant structures of regularly arranged atoms
  • Regular lattice of positive ions (cations)
  • Surrounded by a 'sea' of delocalised electrons
• What are delocalised electrons?


  Electrons that are not bound to an atom and can move freely within the lattice
• Why do metals have delocalised electrons?

  Because metal atoms have a small number of electrons in their outer shells
• What is diamond an allotrope of?


  Carbon
• What are the properties of diamond?

  • Does not conduct electricity
  • Very hard
  • High melting point
• Why does diamond not conduct electricity?

  Because there are no delocalised electrons in the diamond structure
• How many carbon atoms is each carbon atom in diamond bonded to?


  Four other carbon atoms
• Why is diamond very hard?

  Because there are many strong covalent bonds in diamond
• Why is diamond used as a cutting tool?

  Because it is very hard
• What does a high melting point in diamond indicate?


  That a lot of energy is needed to break strong covalent bonds
• What is graphite an allotrope of?


  Carbon
• What are the properties of graphite?


  • Soft
  • Conducts electricity
• How many carbon atoms is each carbon atom in graphite bonded to?

  Three other carbon atoms
• Why is graphite soft?


  Because the layers can easily slide over one another due to weak intermolecular forces
• What makes graphite useful as a lubricant?


  The ability of its layers to slide over one another easily
• Why does graphite conduct electricity?


  Because there is one delocalised electron from every carbon atom that can move freely
• What is graphene an allotrope of?


  Carbon
• What are the properties of graphene?


  • Conducts electricity
  • Light but strong
• Why does graphene conduct electricity?


  Because each carbon atom has a delocalised electron
• What is the thickness of graphene?

  Just 1 atom thick
• Why is graphene considered light yet strong?


  Because it is almost a 2-dimensional structure with strong covalent bonds
• What are the uses of graphene?


  • Electronics
  • Composite materials
  • Solar panels
  • Batteries
• What are fullerenes?


  • Molecules of carbon atoms in hollow structures
  • Usually arranged in hexagonal rings
  • Can also have pentagonal and heptagonal rings
• What is the formula of buckminsterfullerene?

  C60
• What is the shape of buckminsterfullerene?


  Spherical
• Why is buckminsterfullerene considered a simple molecule?


  Because of its fixed size
• What are the common uses of spherical fullerenes?


  • Catalysts
  • Lubricants
  • Vehicles for transporting drugs
• What are carbon nanotubes?

  • Cylindrical fullerenes
  • Often called molecular wires
  • Have a tiny diameter but can be very long
• Why are carbon nanotubes exceptionally strong for their size?


  Because of the strong covalent bonds between carbon atoms
• What are the uses of carbon nanotubes?


  • In electronics
  • In nanotechnology
  • For strengthening materials (e.g. tennis racket frames)