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Chemistry > Alkenes > Flashcards

Alkenes Flashcards

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1
Q

What is the general formula of all Alkenes ?

A

CnH2n

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2
Q

Why do alkenes have limited movement ?

A

Less rotation due to the double bond.

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3
Q

What is the spatial arrangement around a double carbon bond ?

A

Planar

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4
Q

What is the bond angle around a double carbon bond ?

A

120 degrees

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5
Q

What are all single covalent bonds known as and explain this.

A

Sigma bonds

Orbitals overlap to form a sigma bond between two carbon atoms.

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6
Q

What are sigma bonds and how are they caused ?

A

A single Covalent bond between 2 carbon atoms which is cause by the overlapping of 2 orbitals.

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7
Q

What is the covalent bond between a double carbon bond called.

A

A ‘pie’ bobs.

Two 2p orbitals overlap above and below the internuclear axis. This causes a ‘pie’ bond.

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8
Q

How is a pie bond formed and what is it ?

A

A double covalent bond between two carbon atoms. Two 2p orbitals overlap above and below the internuclear axis.

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9
Q

What is a Z isomer ?

A

Atoms on the same side of the isomer.

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10
Q

What is an E isomer ?

A

Atoms on opposite sides of the atom.

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11
Q

Which isomers are Z or E depending on the Mr ?

A

If the atoms with the biggest Mr on the same size, it is the Z isomer.

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12
Q

What is optical isomerism ?

A

A molecule can exist as two isomers which are not superimosed and are mirror images of eachother.

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13
Q

How can optical isomerism be identified ?

A

Optical isomers can rotated polarised light in different directions.

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14
Q

What are the different properties of optical isomers ? What

A 
Identical properties ( melting and boiling points, density)
But different reactivity
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15
Q

Why is a double bond electron rich and what does this cause ?

A

It causes a high electron density and means a highly negative charge.

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16
Q

Why does an electrophile attack a double bond ?

A

Electophiles are electron deficient therefore they accept lone pairs of electrons as they have a positive or slight positive charge.

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17
Q

What are the charges of electrophiles ?

A

Positive or slightly positive

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18
Q

What are electrophiles (1 mark)

A

Electron pair acceptor

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19
Q

What reactions occur when alkenes are attacked by electrophiles ?

A

Electrophillic addition

Addition reaction

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20
Q

What are electrophillic addition reactions ?

A

Alkenes undergo electrophillic addition reactions when they are attacked by electrophiles

21
Q

What causes the slight positive and slight negative charges in diative halogen molecules ?

A

There is an induced dipole.

22
Q

What is the second step of electrophillic addition when using concentrated sulphuric acid ? And why is this done ?

A

Boil in water to produce an alcohol by hydrolysis reaction.

23
Q

What are the 3 electrophiles ?

A

Hydrogen halides
Halogens
Concentrated sulphuric acid

24
Q

Explain how you use bromine to test for alkenes and alkanes.

A

Add hydrocarbon to bromine water and shake.
If the bromine water remains organ/Brown, the hydrocarbon was a saturated alkane.
If the bromine water turns colourless, the hydrocarbon was an unsaturated alkene.

25
Q

What type of hydrocarbon remains orange/ brown in bromine water.

A

A saturated alkane.

26
Q

What type of hydrocarbon makes bromine water turn from brown/orange to colourless ?

A

An u saturated alkene

27
Q

What is a co-ordinate covalent bond ?

A

Both pairs of electrons are donated by the same atom in the covalent bond.

28
Q

What happens in step one of a electrophillic addition reaction ?

A

The ‘pie’ bond of the carbon to carbon double bond breaks forming a carbonation ion which has a positively charged carbon.

29
Q

What happens in step two of an electrophillic addition reaction ?

A

The ion acts as a nucleophile and attacks the carbocation ion.

30
Q

What are symmetrical alkenes ?

A

Alkenes which are unsymmetrical and therefore produce a mixture of products.

31
Q

What are the products of unsymmetrical alkenes ?

A

Unsymmetrical alkenes produce a mixture of products which are minor and major products.
The minor major products and produced based on the relative st abilities of the carbocations which are produced.

32
Q

What are minor products ?

A

Minor products are usually produced in primary carbocation and are less stable carbocation ions.

33
Q

What are major products usually v

A

They are usually tertiary carbocations which are therefore highly stable.

34
Q

What is a primary carbocation ?

A

A carbocation containing one carbon, 2 hydrogens and one R group.

35
Q

What is a secondary carbocation ?

A

A carbocation containing one carbon, one hydrogen and 2 R groups.

36
Q

What is a tertiary carbocation ?

A

A carbocation containing one carbon and 3 R groups.

37
Q

Which types of carbocations are usually major products and why ?

A

Tertiary carbocations as they are more stable.

38
Q

Which types of carbocations are usually minor products and why ?

A

Primary carbocations as they are not very stable.

39
Q

How are poly alkenes produced ?

A

Via catalytic or thermal cracking of crude oil.

40
Q

What are the issues of thermal/ catalytic cracking to obtain polyalkenes ?

A

High energy production costs

Use up non-renewable sources.

41
Q

What are the issues with synthetic polymers ?

A

They are non-biodegradable as they are man made so are non-reactive to most chemicals and bacteria.

42
Q

Why are synthetic polymers mostly non biodegradable?

A

They are man made so are unreactive to most chemicals and bacteria.

43
Q

How are polyalkenes disposed of and what are the issues with this ?

A

They must be burnt but produce toxic.

44
Q

Why is burning polyalkenes for disposal positive ?

A

The energy recovered from burning alkenes can be used to create electricity.

45
Q

What are the advantages of recycling polymers ?

A

Consumption of finite resources is reduced.
Less disposal of plastics required.
Carbon footprint reduced.
Water consumption decreases.

46
Q

Lost the disadvantages of recycling.

A

Transport of materials to a process plant is costly.
Energy consumed in melting of the products.
Transport of new products is costly.

47
Q

What are low density polymers ?

A

Flexible, branches polymers which don’t back easily.

48
Q

What are high density polymers ?

A

Long chain, unbranched rigid polymers which are packed easily.

49
Q

What is life cycle analysis (of polymers?).

A

Quantities the energy and raw materials used and any environmental emissions produced during the extraction of raw materials, original manufacture, recycling, refuse or disposal of a polymer product.

Chemistry (27 decks)

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