Chemistry Unit 2.a

Chemistry Unit 2.a

1. Ionic Bonding

   • Regular Lattice Structure
     • Strong electrostatic forces of attraction
       • Between oppositely charged ions/all directions
   • Similar Properties
     • High Melting/Boiling points
       • Strong attraction
       • A lot of energy needed to overcome attraction
     • When melted, ions are free to move and carry a current
     • Dissolve easily in water

2. Covalent Bonding

   • Simple Molecular Substances
     • Weak intermolecular forces
       • Low melting/boiling points
     • Gases/Liquids at room temp
     • No ions to conduct electricity
   • Giant Covalent Structures
     • No charged ions
       • Doesn't conduct electricity
     • Strong covalent bonds
       • Very high melting/boiling points
     • Only graphite conducts electricity
     • Diamond
       • 4 Covalent Bonds
       • Very rigid
     • Graphite
       • 3 Covalent Bonds - creates layers
         • Free to slide over each other
           • Soft and Slippery
         • Weak intermolecular forces
       • Each carbon has 1 delocalised electron

3. Polymers

   • Thermosoftening
     • Weak intermolecular forces
       • Easy to melt
     • When cools, hardens into new shape
     • Melted and remoulded
     • Individual tangled chains of polymers
       • Free to slide over each other
   • Thermosetting
     • Crosslinks
       • solid structure
     • Strong intermolecular forces
     • Strong, hard, rigid
     • Don't soften when heated
   • Conditions
     • Low Density
       • Heat ethene to 200c under high pressure
     • High Density
       • Lower temp/pressure w/ a catalyst

4. New Materials

   • Smart Materials
     • Depend on conditions eg Temperature
     • Nitinol - shape memory alloy
       • Nickel and Titanium
       • Bend and twist
       • Heat above certain temp - goes back to remembered shape
       • Glasses
         • Put frames in hot water and they go back to shape
       • Braces
         • Warms in the mouth and pulls teeth with it
   • Nanoparticles
     • Include Fullerenes
       • Molecules of carbon shaped like tubes, arranged in hexagon rings
       • Different fullerenes have a different number of carbon atoms
       • Fullerenes have different properties to carbon
     • Covalent bonds make nanotubes very strong
     • Uses
       • Large surface area - catalysts
       • Sensors
       • Strong, light building materials
       • Medicine
       • Electrical circuits
       • Cosmetics

5. Metallic Structures

   • Metals
     • Delocalised electrons from every atom
     • Regular structure
     • Strong forces of electrostatic attraction
     • Atoms slide over each other so can be bent and shaped
   • Alloys
     • Different elements have different sized atoms
     • Distorted Layers
       • Harder to slide
         • So alloys are harder

6. Chromatography

   • Gas
     • Time taken to reach detector is called retention time
     • Position of peaks show retention time of each substance
     • Mass Spectrometer
       • Very accurate
       • Work out Relative Molecular Mass from the graph