C2

• ionic banding

  Electrostatic attraction between positive and negative ions
• Ionic compounds


  • Held together in a giant structure (a regular structure that extends in all directions in a substance, electrostatic attraction between positive and negative ions holds the structure together)
• 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 position)
  • Conduct when molten or dissolved in water (ions free to move)
  • Positive ions: Na, Mg, Al, Ca, Rb
  • Negative ions: Cl, Br, S, O, OH
• Ionic compounds are electrically neutral (positive and negative charges balance out)
• Formation of ionic compounds

  1. Reaction of a metal and a non-metal

  2. Electron transfer occurs - metal gives away electrons in outer shell to non-metal

  3. Metal becomes positive ion, non-metal becomes negative ion
• Covalent bond


  Shared pair of electrons between 2 atoms
• Properties of simple molecular covalent substances

  • Don't conduct electricity (no ions)
  • Small molecules
  • Weak intermolecular forces so low melting/boiling points
  • As mass/size of molecule increases, intermolecular forces increase causing higher melting/boiling points and more energy required to overcome these forces
• Polymers


  Very large molecules with atoms linked by covalent bonds
• Thermosoftening polymers


  • Polymers that melt/soften when heated
  • No bonds between polymer chains, strong intermolecular forces ensure solid at room temp but overcome with heating
• Covalent substances


  • Atoms covalently bonded together in a giant lattice
  • High melting/boiling points due to strong covalent bonds
  • Mostly don't conduct electricity (no delocalised electrons)
  • Examples: diamond, graphite, silicon dioxide
• Diamond


  •Four covalent bonds for each carbon atom, very hard (strong bonds)

  • doesn’t conduct electricity
• Graphite

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


  Hollow shaped molecules, based on hexagonal rings but may have 5/7 carbon rings, Buckminsterfullerene has a spherical shape, simple molecular structure
• Nanotubes


  Cylindrical fullerene with high length to diameter ratio, high tensile strength (strong bonds), conductivity (delocalised electrons)
• Graphene


  A single layer of graphite
• Metallic bonding


  Forces of attraction between delocalised electrons and nuclei of metal ions
• Properties of metals


  • High melting/boiling points (strong forces of attraction), good conductors of heat and electricity (delocalised electrons), malleable, soft (layers of atoms slide over each other whilst maintaining the attraction forces)
• Alloys


  Mixtures of metal with other elements, usually metals, different sizes of atoms distorts the layers, so they can't slide over each other as easily, therefore alloys are harder than pure metals
• Limitations of the simple model - no forces between spheres and atoms, molecules and ions are solid spheres. This isn't true.
• Most metal objects made from alloys - mixtures that contain a metal and at least one other element, pure metals are too soft
• In alloys, the added element disturbs the metal's regular arrangement, the layers don't slide over each other as easily, this means alloys are stronger/harder than regular elements
• Melting and boiling points

  The amount of energy needed to charge state depends on the strength of the forces between the particles of the substance. The stronger the forces, the higher the melting and boiling points.
• A pure substance will melt at a fixed temperature, a mixture will melt over a range of temperatures.
• States of matter


  Solid, liquid, gas
• Nanoscience


  Science that studies particles that are 1-100 nm in size
• Uses of nanoparticles


  • Medicine (drug delivery systems)
  • Electronics
  • Cosmetics (deodorants, sun creams - better UV coverage and more effective protection against cell damage)
• Fine particles


  100-2500 nm diameter
• Coarse particles


  2500-10000 nm diameter
• Nanoparticles have properties different from those for the same materials in bulk because they have a high surface area to volume ratio