Alkenes and Polymers Flashcards
A double bond is made up of what?
A sigma bond and a pi bond.
When is a sigma bond formed?
When two s orbitals overlap.
The two s orbitals overlap in a straight line- this gives the highest possible electron density between the two nuclei.
This is a single covalent bond.
When is a pi bond formed?
When two p orbitals overlap.
Its got two parts to it- one ‘above’ and one ‘below’ the molecular axis. This is because the pi orbitals which overlap are dumbbell shaped.
Why are alkenes much more reactive than alkanes?
Each double bond in an alkene sandwiches the pi and sigma bond in the middle.
Because there’s two pairs of electrons in the bond, the C=C double bond has a really high electron density.
Also, the pi bond sticks out above and below the molecule so more likely to be attacked by electrophiles.
Why can’t the carbon atoms in the C=C double bonds rotate?
The p orbitals have to overlap to a form a pi bond.
The C=C double bond and the atoms bonded to these carbons are planar (flat) and rigid (they can’t bend or twist much).
The restricted rotation around the C=C double bond is what causes cis-trans/E/Z isomerism.
The double bonds in alkenes can open up and join together to make long chains called…
Polymers. This is called addition polymerisation.
What are the uses of poly(chloroethene)?
It is made to use water pipes, for insulation on electric wires and as a building material.
What are the uses of poly(tetrafluoroethene)?
It is chemically inert and has non stick properties.
Making it an ideal coating for frying pans.
What is addition polymerisation?
The formation of poly(ethene) from ethene is an example of addition polymerisation.In addition polymerisation small unsaturated monomers (monomers with carbon to carbon double bonds) join up by the opening of the double bond allowing them to join up to form a long carbon chain.
