Chapter 13 Flashcards
What are orbitals?
Regions around the nucleus which can hold up to 2 electrons
What are sigma bonds?
Head-on overlap of 2 orbitals. It is positioned on a line directly between 2 bonding atoms and are single bonds.
What are Pi bonds?
Pi bonds are formed by the sideway overlap of 2 p orbitals. It results in a high electron density above and below the sigma bond. It locks the 2 atoms in position and prevents rotation around the double bond.
Characteristics of Alkenes
General formula is CnH2n It is aliphatic with 1 double bond 120° Trigonal planar Has sigma and pi bonds
Pi bonds vs Sigma bonds
Pi bonds: Overlap of p orbitals 2nd bond in a double bond Above and below the plane of Carbon atoms Sigma bonds: Overlap of any orbitals Single bonds On the plane of Carbon atoms
What are stereoisomers?
Stereoisomers have the same structural and molecular formula but have a different arrangement of atoms in space. There are 2 types:
E/Z isomers
Optical isomerism
What is E/Z isomerism?
It occurs due to the rigidity of the C=C bond
The pi bond above and below the carbon atoms restrict the carbons from being able to rotate
The 2 conditions needed for E/Z isomerism to occur are a C=C bond and different groups attached to each carbon in the double bond
What is Cis/Trans isomerism?
Cis/trans isomerism is a special kind of E/Z isomerism where 1 group of the groups attached to each carbon has to be a hydrogen
Reactivity of alkenes
Alkenes are more reactive than alkanes due to the presence of a pi bond. Pi bonds are easier to break down
Addition reactions of alkenes
Hydrogen in presence of a nickel catalyst
Halogens
Hydrogen halides
Steam in the presence of an acid catalyst
Hydrogenation
It produces an alkane
The hydrogen is added across the double bonds
Halogenation
Alkenes undergo a rapid addition reaction with the chlorine, bromine and iodine
It can be used to test for a double bond as the colour of the halogen becomes colourless
Produces haloalkanes
Addition reactions of alkenes with hydrogen halides
Reacts with gaseous hydrogen halides at room temperature to form haloalkanes
Forms haloalkanes
There can be 2 products
Hydration reaction of alkenes
Alcohols are formed
Alkenes react with steam
Steam adds across the double bond
Can form 2 possible products
What is an electrophile?
An electrophile is an atom or group of atoms that are attracted to electron-rich centres and can accept an electron pair. It is usually a positive ion or molecule containing a partial positive charge.
What is a nucleophile?
A nucleophile is a chemical species that donates an electron pair to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond can act as nucleophiles
What is carbocation stability?
Each alkyl group will donate and push electrons towards the positive charge of the carbocation.
If there are more alkyl groups, the positive charge will be spread out more and therefore will make it more stable. The carbocation formed is more likely to be the more stable carbocation.
What is Markownikoff’s rule?
When a hydrogen halide reacts with an unsymmetrical alkene, the hydrogen of the hydrogen halides attaches itself to the carbon atom of the alkenes with the greater number of hydrogen atoms.
What is addition polymerisation?
Unsaturated alkene molecules produce long saturated chains containing no double bonds. Industrial polymerisation is carried out at high temperatures and high pressure using catalysts
What is recycling?
Recycling polymers reduces their environmental impact by conserving finite fossil fuels and decreasing the amount of waste. Polymers are sorted then chopped into flakes, washed, dried then melted. Then it is cut into pellets and used by manufactures.
What is PVC recycling?
Disposal and recycling of PVC is hazardous due to high chlorine content
Can be grounded up or use solvents to dissolve and recovered using precipitation
What can waste polymers also be used as?
Waste polymers can be burned to produce heat, generating steam to generate electricity
What is feedstock recycling?
Describes the chemical and thermal processes that can reclaim oil, monomers or gasses from waste polymers.
The products can be used as raw materials to produce new polymers.
Polymers can be unsorted and still be recycled
What are biodegradable and photodegradable polymers?
Biodegradable polymers are broken down by microorganisms into water, carbon dioxide and biological compounds. They are made from starch or cellulose.
Photodegradable polymers are weakened by light instead
