4.1.3

• Alkene general formula : Cn H2n
• Alkenes are unsaturated
• Bond angle around a Alkene double bond is 120 (planar)
• In Alkenes carbons form sp2 and one 2p orbital
• The 2p orbital on each carbon in an alkene double bond overlaps sideways to form a pi bond
• The remaining 2p orbital of an alkene in a double carbon bond overlaps with the other directly between the bonding atoms forming a pi bond
• Double carbon bonds are stronger than single carbon bonds
• Double carbon bonds are formed from a pi and sigma bond
• Sigma bonds are stronger than pi bonds
• An Alkene double bond is an area of high electron density and negativity that attracts electrophiles
• Electrophiles : an electron pair acceptor
• Adding hydrogen is called hydrogenation
• reactions involving electrophiles joining are called electrophilic addition mechanisms
• Mechanisms contain: partial charges, lone pairs, ionic charge, curly arrows
• Carbocation: positive carbon ion
• cyclohexane + bromine water -> orange and yellow layers
• cyclohexene + bromine water -> clear and white precipitate, presence of carbon double bond
• markownikoffs rule

  A) major

  B) minor

  
• monomers: small molecules, a single unit
• polymers: multiple monomers joined together in repeating units
• repeating units: small structures/ arrangements occurring over and over again
• addition polymerisation flowchart: crude oil -> fractional distillation -> cracking -> polymerisation
• during polymerisation the pi bond in the double carbon bond is broken and a new sigma bond is formed
• a polymer is surrounded by brackets and has a small n to represent the number of repeating monomers
• monomer -> polymer:

  A) =

  B) -

  
• for complex polymers draw the repeating unit and condense the rest of the carbon chain

  
• landfill: the disposal of waste material by burying it in a lined pit until it is full and recovered.

  x - plastics cannot break down due to lack of light water and oxygen
• combustion: burning plastics

  + - release energy to generate electricity

  x - releases co2 and acidic gases ( the can be counteracted by base gas scrubbers)
• reusing and recycling: using again or making something new

  + - carry out a function many times

  x - plastic must be sorted, expensive, concerns about quality and contamination
• organic feedstock: polymers are broken into small organic molecules to be used in industrial reactions, a type of recycling
• biodegradable polymers: break down via organisms and environmental conditions. contain plant starch and addition polymers

  x - addition polymers still released into the environment
• bioplastic: a polymer made from renewable sources, can be considered carbon neutral if sustainable farming methods are used, fully biodegradable
• photodegradable polymers: break down using energy wavelengths similar to light, affects bonds directly or an additive, cannot be stopped once it starts. must have sufficient light exposure ( that landfills don't have)
• pi bond formation

  A) sideways overlap

  B) p orbitals

  C) pi bond

  
• toxic gas HCl is neutralised by being passed through an alkali or carbonate
• a carbon ring causes a hydrocarbon to loose 2 hydrogen atoms
• reactivity of alkenes

  the pi bond is weaker than the sigma bond so is much easier to break so is more reactive
• alkene + hydrogen

  requires nickel catalyst and 150c, forms alkane
• alkene + halogen

  requires RTP, forms dihaloalkane
• alkene + steam

  requires phosphoric (V) acid catalyst, 300c and 65 atm , produces alcohol