Alkanes and Alkenes

• Electrophillic Addition: A reaction in which a nucleophile attacks a carbon atom with a lone pair of electrons
• Carbocation: A carbocation is a carbonyl group that is bonded to a carbon atom
• A primary, secondary and tertiary carbocation is classified by the amount of R groups present
• R groups push electron density towards the positive carbon, stabilising it. This is known as the Inductive Effect
• Markovnikov's Rule: Hydrogen will bond to the Carbon with the most Hydrogen atom attached
• Major products are formed using Markovnikov's Rule whilst minor products aren't
• Polymer: A large molecule made up of many small molecules joined together
• Monomer: A molecule that can be combined to form a polymer
• Addition Polymerisation: Monomer units add onto each other without forming any new bonds
• Examples of Natural Polymers:

  • Starch
  • Proteins
  • Cellulose
  • DNA
• Bakelite is an example of a synthetic polymer
• Plasticiser: Small molecules that get between polymer chains and allow polymer chains to slide over each other
• New polymers have been created over time with specific properties for certain jobs
• There are van der waals forces between the polyalkene chains. As the Mr of these chains are high, they are solids at room temperature
• The less branched the polymer chains are, the more dense the plastic and the stronger the van der waals forces. This increases the melting point and makes the plastic stronger
• Low Density Polyethene (LDPE)

  • 200 C
  • 2000 atm
  • O2
  • Molecules loosely packed due to branching due to free radical mechanism
  • Flexible and soft
  • Used to make bags and cling flim
• High Density Polyethene (HDPE)

  • 60C
  • 2 atm
  • Molecules Tightly Packed
  • Denser, Stiffer, Harder
  • Buckets, Bottles
• Isotatic Polypropene:

  • Strong
  • Used in crates, carpets and ropes
• Atactic Polypropene:

  • Softer
  • Lower MP
  • Used in tape, sealants
• Biodegradability:

  • Polyalkenes are saturated (like alkanes).
  • Non-polar bonds.
  • Very unreactive, a useful property.
  • Not attacked by biological agents e.g. enzymes so are non-biodegradeable.
  • Waste disposal an issue.
• Solutions to pollution by plastics - Mechanical recycling

  • Separate different types of plastic.
  • Washed, sorted and ground into pellets.
  • Pellets can be melted and remoulded
• Solution to pollution by plastics - Feedstock Recycling

  • Plastics heated to break polymer chains and form monomers to make new plastics.
  • Thermoplastic polymers soften when heated so can be melted and re-used, this can only be a few times before the chains break and degrade the plastic’s properties.