Structure and Bonding

• What is ionic bonding?


  The electrostatic attractions between positive and negative ions, it is a relatively strong attraction!
• How are ionic compounds held together?

  -held together in a giant lattice

  -it is a regular structure that extends in all directions of the substance

  -Electrostatic attraction between positive and negative ions holds the structure together
• State the properties of ionic substances


  -high melting and boiling point ( due to the strong electrostatic forces between them)

  -do not conduct electricity when solids as ions are in a fixed position

  -conduct when molten or dissolved in water as the ions are now free to move!
• What two materials does ionic bonding occur between?


  Metal and non-metal!
• Give five examples of positive ions and five examples of negative ions!


  POSITIVE : Na+, Mg2+, Al3+, Ca2+, Rb+

  NEGATIVE: Cl-, Br- , SO42-, NO3-, OH- (chloride, bromide, sulfate, nitrate, hydroxide)

  Ionic compounds are electrically neutral, ie positive and negative charges balance eachother out!
• What kind of diagram does ionic bonding require?


  diagram with two boxes

  
• How are ionic compounds made, explain in terms of MgO


  • reaction between a metal and non metal
  • electron transfer occurs, metal gives away its outer shell electrons to the non metal
  • Mg is group 2 therfore it has 2 available outer shell electrons to give out
  • O is in group 6, meaning it can accept 2 electrons to get a full outer shell configuration
  • Mg becomes Mg2+ and oxygen becomes O2-
• What is a covalent bond?

  A Covalent bond is a shared pair of electrons between two atoms! (non-metal and non-metal)
• Describe the structures and properties of simple molecular covalent substances!

  • Do not conduct electricity (no ions)
  • Small molecules
  • Weak intermolecular forces
  • Low melting and boiling points
• How do intermolecular forces change as the mass/size of the molecule increases?


  -they increase

  -that causes the melting and boiling points to also increase as more energy is now needed to overcome those forces!
• What are polymers and what are thermosoftening polymers?


  Polymers are very large molecules with atoms linked by covalent bonds!

  -Thermosoftening polymers : special type of polymer that melt/soften when heated, there are no bonds between the polymer chains, strong intermolecular forces ensure that the structure is a solid at room temperature, yet those forces are overcome with heating making the polymer melt.
• What are giant covalent structures?

  -Solids, atoms covalently bonded together in a giant lattice

  -High melting and boiling points - strong covalent bonds

  -most do not conduct electricity due to having no delocalised electrons

  eg: diamond, graphite and silicon dioxide
• Name and describe two carbon allotropes

  DIAMOND:

  -four, strong covalent bonds for each carbon atom

  -very hard (strong bonds)

  -very high melting point (strong bonds)

  -does not conduct electricty or charges as it has no delocalised electrons

  GRAHITE:

  -three covalent bonds for each carbon atom

  -layers of hexagonal rings

  -high melting point

  -layers are held together by weak intermolecular forces between layers - soft (can be used as lubricant)

  -conduct thermal and electricity due to one delocalised electron per each carbon atom, and delocalised electrons are free to move between layers!
• Name and describe Fullerenes, Nanotubes and graphene


  FULLERENES (Buckminsterfullerene)

  -hollow shaped molecules, based on hexagonal rings but may have 5/7 carbon rings, formula is C60 and has a spherical shape, with a simple molecular structure

  NANOTUBES:

  -cylindrical fullerene with a high length to diameter ratio, with high tensile strenght (due to its strong bonds), and great conductivity (due to its delocalised electrons)

  GRAPHENE: a single layer of graphite!
• What is metallic bonding?


  The forces of attraction between delocalised electrons and positive metal ions!
• Describe properties of metals


  -High melting and boiling points (due to the strong forces holding them together)

  -good conductors of heat and electricity (delocalised electrons)

  -malleable, soft (layers of atoms can slide over each other whilst maintaining the attraction of forces between them!)
• What are alloys, why are they harder than pure metals?


  ALLOYS:

  -mixtures of metals with other elements usually metals!

  -different sizes of atoms distorts the layers, so they cant slide over eachother, therefore alloys are harder than pure metals!
• Define the properties of simple covalent bonds


  MELTING / BOILING POINTS : low - because of weak intermolecular forces between molecules

  CONDUCTIVITY (SOLID) : poor - no ions do conduct

  CONDUCTIVITY (MOLTEN) : poor - no ions

  GENERAL DESC : mostly gases and liquids
• Define the properties of ionic bonds


  BOILING/MELTING POINT : high - because of giant lattice of ions with strong forces between oppositely charged ions

  CONDUCITIVITY (SOLID) : poor - ions cant move

  CONDUCTIVITY (MOLTEN) : good - ions are free to move

  GENERAL DESC : crystalline solids
• Describe the properties of giant covalent bonds

  BOILING/METLING POINT : high - beacuse of many strong covalent bonds between atoms in the giant structure

  CONDUCTIVTIY (SOLID) : [ diamond and sand = poor as the electrons cant move ] [graphite = good as delocalised electrons can move freely through the structure ]

  CONDUCTIVITY (MOLTEN) : poor

  GENERAL DESC: solids
• Define the properties of metallic bonds


  BOILING/MELTING POINT : high - strong electrostatic forces between positive ions and delocalised electrons

  CONDUCTIVITY (SOLID) : good - delocalised electrons are free to move through structure

  CONDUCTIVITY (MOLTEN) : good

  GENERAL DESC : shiny metal solids
• What are the limitations of the simple model of atomic structure?

  -There are no forces between the spheres and atoms,

  -molecules and ions are solid spheres - this is not true
• What does the amount of energy needed to change state from solid to liquid (or liquid to gas) depend on?

  -The strength of the forces between the particles in the substance

  -The nature of particles involved depends on the type of bonding and the structure of the substance

  -The stronger the forces between the particles the higher the melting and boiling point of the substance!
• A pure substance will melt or boil at..? What about the mixture?


  A pure substance will melt/boil at a fixed temperature

  A mixture will melt over a range of temperatures!
• What are the three states of matter?

  Solid, Liquid, Gas
• What is nanoscience?


  Science that studies particles that are 1 - 100nm in size! (teeny)
• State the uses of nanoparticles


  • Medicine (drug delivery systems)
  • Electronics
  • Deodorants
  • Sun creams (better skin coverage and more effective protection against cell damage)
• What are fine and coarse particles?


  -Fine particles (soot) are 100-2500 nm diameter

  -Coarse particles (dust) are 2500-10^5 nm in diameter
• What is the formula to convert from nm to m?


  m = nm / 1,000,000,000
• Why do nanoparticles have different properties to those for the same materials in bulk?


  They have a significantly larger surface area to volume ratio!