Chapter 13 - Alkenes Flashcards
What is the general formula for alkenes?
CnH2n
How is a double bond formed?
Starts with 3 sigma bonds forming.
1 electron is left in the p-orbital.
Pi bond forms from the sideways overlap of 2 p-orbitals.
What stops rotation in alkenes?
The pi bond locks the 2 carbons in position, so alkenes cannot be rotated.
What is the shape around the carbons in the double bond and why?
Trigonal planar because theres 3 regions of electron density around each carbon, which repel each other, all in the same plane.
What are uses of polypropene?
Children’s toys,
Packing crates
Guttering
What are the uses of polyphenylethene aka polystyrene?
Packaging material
Food trays and cups
Because of its thermal insulating properties
What is the downside of current disposal of waste polymers?
Very unreactive so are non-biodegradable, with negative environmental effects.
What are the benefits of recycling polymers?
Reduces environmental impact by conserving fossil fuels and decreasing waste.
What are the weaknesses of recycling polymers?
Polymers have to be sorted by type. They can’t be mixed because they would become unusable.
What are the dangers of PVC (Polychloroethene) disposal?
High chlorine content and range of additives present make it hazardous.
When burnt it releases corrosive hydrogen chloride gas.
How can polymers be used as fuel?
They can be burned to produce heat.
What is feedstock recycling?
Chemical and thermal processes that can reclaim monomers and gases from waste polymers.
What is a major advantage of feedstock recycling?
Able to handle unsorted and unwashed polymers.
What are biodegradable polymers?
Polymers made from renewable sources and can be broken down by microbes.
Made from starch or cellulose.
How is a sigma bond formed?
Head on overlap of orbitals of 2 bonding atoms,
With electron density centred around a line directly between the nuclei of bonding atoms.
What is a pi bond?
A sideways overlap of 2 p-orbitals with electron density above and below the plane of bonding atoms.
What is a reaction mechanism?
A series of steps that shows how a reaction takes place
What is an electrophile?
An atom or group of atoms that is attracted to an electron-rich centre and accepts an electron pair.
What atom or molecule is usually an electrophile?
Positive ions or molecules with an atom that has a δ+ charge
How does a double bond attract electrophiles?
It represents a region of high electron density due to the presence of π electrons, which attracts electrophiles.
Why are alkenes more reactive than alkanes?
Because the π bond electrons are more exposed than the σ bond electrons, so the π bond breaks more easily
What is a monomer?
A small molecule that combines with many other monomers to form the polymer.
What is a repeat unit?
The arrangement of atoms that occurs in the polymer structure over and over again.
