Because they all have atleat one double bond and so can make extra bonds with extra atoms in addition reactions.
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What is the formula of propene?
C3H6
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What is the structural formula of Butene?
CH3CH=CHCH3
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How is a sigma bond formed?
When 2 S orbitals overlap.
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What is the shape of an S orbital?
Spherical.
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How do the S orbitals overlap? And what does it make?
In a straight line which gives the highest possible electron density between the two nuclei. It makes a single covalent bond.
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How is a pi bond formed?
When two P orbitals over lap.
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Why does a pi bond have two parts to it?
There is an upper attraction and a lower attraction because P orbitals are dum bell shaped.
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If you were to describe the double bond in an alkane like a hot dog, how would you describe it?
The Pi bond acts as the bread bun on either side and the sigma bond is sandwiched in the middle like a sausage.
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Why does a carbon-carbon double bond have a really high electron density?
Because there are two pairs of electrons in the bond.
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What does having a really high electron density mean for an alkane?
It makes it very reactive.
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What other reasons are there for an alkenes high reactivity?
The pi bond sticks out above and below the rest of the molecule which means it is likely to be attacked by electrophiles.
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What is an electrophile? And what is its charge?
An electrophile is something which is attracted to electron-rich regions in other molecules or ions. Always positive or atleast slightly positively charged.
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What is a use of alkenes due to their reactivity?
They are handy starting points for making other organic compounds and for making petrochemicals.
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Why can't the carbon-carbon double bond in an alkene rotate?
Because the p orbiatals have to overlap to form a pi bond. The double bond and the atoms bonded to these carbons are FLAT and RIGID and so can't twist or bend.
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How are some alkenes different when referring to being 'planar'?/What does this mean?
Smaller alkenes are completely planar but in large alkenes only the carbon to carbon double bond is planar. This means atoms can still rotate around single bonds within the molecule.
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What causes cis/trans isomerism? (Could also be called e/z)
The lack of rotation around a carbon carbon double bond.
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How are polymers made?
By the breaking of the double bonds in alkenes to make long chains.
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What are the individual, small alkenes called?
Monomers
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What is the term for making a polymer from an alkene?
Addition polymerisation. For instance you would say poly(ethene) is made by the addition polymerisation of ethene.
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What must you include when drawing a polymer to get the marks?
The brackets or side links must stick out of the brackets to show that this is a repeating unit. The N outside of the brackets to show that there are lots of these chains.
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How do we find the monomer used to form an additional polymer?
You take the repeating unit and add a double bond.
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Can you polymerise other molecules other than basic alkanes? Give an example if so.
Yes. You can polymerise chloroethene to make poly(chloroethene), or PVC.
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What are some uses of poly(chloroethene) or PVC?
It can be used to make water pipes, for insulation on electric wires and as a building material.
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What is the polymer of tetraflouroethene?
Poly(tetrafluoroethene) or PTFE.
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What is special about poly(tetrafluorothene)?
It is chemically inert.
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What is the meaning of bein chemically inert
It means very unreactive.
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Why is poly(tetrafluoroethene) used as a coating for frying pans?
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