3.04 Alkenes

• how do plasticisers work?

  They get between the polymer chains and push them apart, reducing the strength of the VDWs allowing them to slide more and bend.
• What are plasticisers?

  Molecules added to polymers to make them more flexible.
• What are addition polyalkenes held together by? And how does there structure affect their use?

  They are held together by VDWs, long straight chains have stronger VDWs because they are closer together meaning they are strong and rigid.

  
  

  Short branched chains have weaker VDWs and are therefore more flexible and weaker.
• Why are polyalkenes unreactive?

  They are saturated and therefore non polar
• What are the two types of polymers?

  Natural e.g. DNA or proteins

  
  

  Synthetic e.g. poly(ethene), nylon, Kevlar
• What are addition polymers?

  Polymers formed from alkenes, they are unreactive and have several uses.
• What are polymers?

  Long molecules made of many smaller monomer units joined by polymerisation.
• What is the test for alkenes?

  Bubble into bromine water, if Alkene is present the solution will turn from orange to colourless.
• How do you get from an Alkene to an alcohol?

  Hydration / electrophillic addition with a strong acidic catalyst.
• How do you get from an Alkene to a alkyl hydrogen sulphate?

  Electrophilic addition with concentrated H2SO4 at room temp.
• What happens when the Alkenes is unsymmetrical during electrophilic addition?

  Two products are produced and the amount of each is dependant on the stability of the carbocation. This is because alkyl groups push electron towards the positive carbon stabilising it.
• How do you get from an Alkenes to a haloalkane?

  Electrophilic addition with a polar halogen bond e.g. HBr HCl
• What are electrophiles?

  electron pair acceptors.

  
  

  They can be positively charged ions e.g. H+, NO2+, polar molecules e.g. HBr, H2SO4, or temporary dipoles in diatomic halogens e.g. Br2.
• Why are alkenes more reactive than alkanes?

  Electrons in C=C are held less tightly so they can attractive positive ions or positive ends of polar molecules.
• How do pi bonds increase Alkenes reactivity?

  They have a high electron density which makes it easier for them to attract positively charged ions or positive ends of polar molecules, increasing its reactivity.
• How are covalent bonds formed?

  sharing of electrons / overlapping orbitals
• What is a pi bond?

  double covalent bond
• What is a sigma bond?

  single covalent bond
• What is the general formula for alkenes?

  CnH2n
• What are alkenes?

  unsaturated hydrocarbons
• How do plasticiser molecules work?

  The plasticiser molecules fit in the gaps between the polymer chains, pushing them apart Intermolecular forces between chains are reduced in strength, and so the polymer gets easier to bend
• How do longer chain polyalkenes compare to short chains?

  Long straight chains will be strong and rigid due to the strong intermolecular van der Waals forces Short branched chains will be weaker and more flexible