C2.2 Structure and Properties

C2.2 Structure and Properties

1. Giant Ionic Structures

   • Ions arranged in a lattice, with strong electrostatic forces
   • High melting/boiling points as more energy needed to break bonds
   • Solid ionic compound can not conduct electricity as they are in fixed position. Liquid, ions can move so conduct
   • Many dissolve in water. Lattice split by water molecules. Ions are free to move, form a solution, conduct

2. Simple Molecules

   • Covalent bonds have low melting points
   • Intermolecular forces
     • Covalent have weak forces but strong bonds
       • Atoms in molecule are tight together
       • Energy between molecules is weak
   • No overall charge so no chance of conducting electricity

3. Giant Covalent structures

   • AKA Macromolecules
   • Diamond, graphite and silicon dioxide
   • Held by strong convalent bonds
   • Hard, high melting points,
   • Graphite has layers
   • Bonding in graphite
     • Carbon arranged in hexagons
     • Has delocalised electrons
       • can conduct
   • Fullerenes
     • Ball/cage shape
     • Can place things inside the cage
       • medicine?

4. Giant Metallic Structures

   • closely packed layers
   • Alloys are mixtures of metals, they are harder as the layers can not slide as easily
   • Explaining the properties
     • positive ions are held together by a glue of delocalised electrons
     • these electrons can move so allow a lattice to distort
   • Shape Memory Alloys
     • When heated return to their original state
     • braces and bone broken things

5. Properties of Polymers

   • Different Monomers
     • monomers affect the properties of the polymer
   • Different reaction conditions
     • High pressures and a trace of oxygen, ethene makes low density polyethene
       • Polymer chains are Banches
     • Catalyst at 50°C and slight pressure makes High Density Polyethene
       • Chains are closer
   • Thermosoftening and thermosetting polymers
     • Thermosoftening melt and untangle their chains
     • Thermosetting do not melt as they have cross links
   • Bonding
     • Thermosoftening is weak

6. Nanoscience

   • Science of the smallest of things
   • nanoparticles behave differently from the materials they are made from
   • New developements are always good but more research into problems are needed