Bonding, structure and the properties of matter

• what is ionic bonding?

  • electrostatic attraction between positive and negative ions
  • relatively strong attraction
• how are ionic compounds held together?

  • in a giant lattice
  • regular structure that extends in all directions in a substance
  • electrostatic attraction between positive and negative ions holds the structure together
• state properties of ionic substances

  • high melting and boiling points (strong electrostatic forces between oppositely charged ions)
  • don’t conduct electricity when solid (ions in fixed positions)
  • conduct when molten or dissolved in water - ions are free to move
• give 5 examples of positive and negative ions.

  what is important when working out a formula of an ionic compound?

  • P: Na+ Mg2+ Al3+ Ca2+ Rb+N: Cl- Br- SO2-4 No-3 OH-
  • ionic compounds are electrically neutral
• how are ionic compounds formed?

  • reaction of a metal with a non-metal
  • electron transfer occurs - metal gives away its outer shell electrons to non-metal
• what is a covalent bond?

  shared pair of electrons between 2 atoms
• describe the structure and properties of simple molecular covalent substances

  • don’t 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?

  • increase
  • causes melting/boiling points to increase as well (more energy needed to overcome these forces)
• what are polymers? What are thermosoftening polymers?

  • very large molecules with atoms linked by covalent bonds
  • special type of polymers, melt/soften when heated, no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature, forces are overcome with heating - polymer melts
• what are giant covalent substances? give examples.

  • solids, atoms covalently bonded together in a giant lattice
  • high melting/boiling points - strong covalent bonds
  • mostly don’t conduct electricity 
  • diamond, graphite, silicon dioxide
• name the allotropes of carbon

  • diamond
  • fullerenes
  • graphite
  • nanotubes
  • graphene
• describe and explain diamond

  • four, strong covalent bonds for each carbon atom
  • very hard, strong bonds
  • very high melting point
  • doesn’t conduct
• describe and explain graphite

  • three covalent bonds for each carbon atom
  • layers of hexagonal rings
  • high melting points
  • layers free to slide as weak intermolecular forces between layers,
  • soft, can be used as lubricant
  • conduct thermal and electricity due to one delocalised electron per each carbon atom
• describe and explain fullerenes

  • hollow shaped molecules
  • based on hexagonal rings but may have 5/7 carbon rings
  • C60 has spherical shape, simple molecular structure (buckminsterfullerene)
• describe and explain nanotubes

  • cylindrical fullerene with length to diameter ratio
  • high tensile strength (strong bonds)
  • conductivity (delocalised electrons)
• describe and explain graphene

  single layer of graphite
• what is metallic bonding?

  forces of attraction between delocalised electrons and nuclei of metal ions
• describe properties of metals

  • high melting/boiling points (strong forces of attraction)
  • good conductors of heat and electricity (delocalised electrons)
  • malleable, soft (layers of atoms can slide over each other whilst maintaining the attraction forces)
• what are alloys? why are they harder than pure metals?

  • mixtures of metal with other elements, usually metals
  • different sizes of atoms distorts the layers so they can’t slide over each other, making them harder than pure metals
• describe the properties of simple covalent structures

  • low boiling and melting points due to weak intermolecular forces between molecules
  • poor conductivity when solid as no ions to conduct
  • poor conductivity when molten as no ions
  • mostly gases and liquids
• describe the properties of ionic structures

  • high melting/boiling points due to giant lattice of ions with strong forces between oppositely charged ions
  • poor conductivity when solid as ions can’t move
  • good conductivity when molten as ions are free to move
  • crystalline solids
• describe the properties of giant covalent structures

  • high boiling/melting points due to many strong covalent bonds between atoms
  • poor conductivity when solid in diamond and sand as electrons can’t move
  • good in graphite as free delocalised electrons between layers can move
  • poor conductivity when molten
  • generally solids
• describe the properties of metallic structures

  • high melting/boiling points as strong electrostatic forces between positive ions and delocalised electrons
  • good conductivity when solid as delocalised electrons are free to move through the structure
  • good conductivity when molten
  • generally shiny metal solids
• what are the limitations of the simple model?

  • shows particles as spheres
  • doesn’t take into account different sizes of particles
  • no forces are shown
  • spheres are shown as solid
• what does the amount of energy needed to change state from solid to liquid or liquid to gas depend on?

  • strength of the forces between the particles of the substance
  • nature of the 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/boiling point of the substance
• a pure substance will melt or boil at…

  • a fixed temperature
  • a mixture will melt over a range of temperatures
• 3 states of matter

  solid, liquid and gas
• what is nanoscience?

  science that studies particles that are 1-100nm in size
• 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) 100-2500 nm diametercoarse particles (dust) 2500-10^5 nm diameter
• why do nanoparticles have different properties to those for the same materials in bulk?

  high surface area to volume ratio