General

• Ionic bonding

  Electrostatic attraction between positive and negative ions. It is a relatively strong attraction.
• How ionic compounds are held together

  1. They are held together in a giant lattice

  2. It's a regular structure that extends in all directions in a substance

  3. Electrostatic attraction between positive and negative ions holds the structure together
• Properties of ionic substances

  • High melting and boiling point (strong electrostatic forces between oppositely charged ions)
  • Do not conduct electricity when solid (ions in fixed positions)
  • Conduct when molten or dissolved in water - ions are free to move
• Examples of positive ions


  • Na+
  • Mg2+
  • Al3+
  • Ca2+
  • Rb+
• Examples of negative ions

  • Cl−
  • Br−
  • SO4 2−
  • NO3−
  • OH−
• Ionic compounds are electrically neutral, i.e. positive and negative charges balance each other
• How ionic compounds are formed (MgO case)

  1. Reaction of a metal with a non-metal

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

  3. Mg becomes Mg2+ and O becomes O2− (oxide)
• Covalent bond

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

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

  They increase. That causes melting/boiling points to increase as well (more energy needed to overcome these forces)
• Polymers


  Very large molecules (>100s, 1000s of atoms) with atoms linked by covalent bonds
• Thermosoftening polymers

  Special type of polymers; they melt/soften when heated. There are no bonds between polymer chains. Strong intermolecular forces ensure that the structure is solid at room temperature. These forces are overcome with heating - polymer melts
• Giant covalent substances

  • Solids, atoms covalently bonded together in a giant lattice
  • High melting/boiling points – strong covalent bonds
  • Mostly don't conduct electricity (no delocalised e−)
  • Examples: diamond, graphite, silicon dioxide
• Properties of diamond

  • Four, strong covalent bonds for each carbon atom
  • Very hard (Strong bonds)
  • Very high melting point (strong bonds)
  • Does not conduct (no delocalised electrons)
• Properties of 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
• Properties of fullerenes

  • Hollow shaped molecules
  • Based on hexagonal rings but may have 5/7-carbon rings
  • C60 has spherical shape, simple molecular structure (Buckminsterfullerene)
• Properties of nanotubes

  • Cylindrical fullerene with high length to diameter ratio
  • High tensile strength (strong bonds)
  • Conductivity (deloc. electrons)
• Graphene is 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 can slide over each other whilst maintaining the attraction forces)
• Alloys

  Mixtures of metal with other elements, usually metals
• Alloys are harder than pure metals because the different sizes of atoms distorts the layers, so they can't slide over each other
• The simple model has limitations as there are no forces between spheres and atoms, molecules and ions are solid spheres - this is not true
• The amount of energy needed to change state from solid to liquid or liquid to gas depends on the strength of the forces between the particles of the substance
• A pure substance will melt or boil at a fixed temperature, while a mixture will melt over a range of temperatures
• The three states of matter

  • Solid
  • Liquid
  • Gas
• Nanoscience

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

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

  • Fine particles (soot), 100-2500 nm diameter
  • Coarse particles (dust), 2500-105 nm diameter
• Nanoparticles have different properties to those for the same materials in bulk due to their high surface area to volume ratio