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Subjects > Chemistry-Module 4 > Flashcards

Chemistry-Module 4 Flashcards

1
Q

What is a functional group?

A

A group of atoms responsible for the characteristic reactions of a compound.

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2
Q

What is a homologous series?

A

A series of organic compounds with the same functional group but each successive member has one more CH2 group.

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3
Q

What does a molecular formula show?

A

The actual number of atoms of each element in a molecule.

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4
Q

What does a structural formula show?

A

The atoms carbon by carbon with the attached hydrogens and functional groups.

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5
Q

What does the displayed formula show?

A

How all the atoms are arranged and all of the bonds between them.

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6
Q

What does the skeletal formula show?

A

The bonds of the carbon skeleton only with any functional groups.

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7
Q

What is a general formula?

A

The simplest algebraic formula of a member of a homologous series.

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8
Q

Describe aromatic compound?

A

Contains a benzene ring

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9
Q

Describe aliphatic compounds

A

Contain carbon and hydrogen joint together in straight chains, branched chains or non-aromatic rings.

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10
Q

What are alicyclic compounds?

A

Compounds arranged in non-aromatic rings with or without side chains.

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11
Q

What is the general formula of alkyl groups?

A

CnH2n+1

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12
Q

Describe are saturated compounds?

A

Contain single carbon-carbon bonds only

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13
Q

Describe unsaturated compounds?

A

Contain multiple carbon-carbon bonds including double bonds, triple bonds and aromatic rings.

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14
Q

Define structural isomers

A

Compounds with the same molecular formula but different structural formulas.

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15
Q

Determine a chain isomer

A

The carbon skeleton can be arranged differently e.g. as a straight chain or branched.

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16
Q

Determine a positional isomer

A

the skeletal and functional group is the same but the functional groups are attached to different carbon atoms.

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17
Q

Determine a functional group isomer

A

The same atoms arranged into different functional groups.

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18
Q

What is an alkane?

A

A saturated hydrocarbon that only contains single C-C and C-H bonds.

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19
Q

What are the IUPAC rules of nomenclature?

A
  1. Count the carbon atoms in the longest continuous chain
  2. Use the main functional group to determine the homologous series
  3. Number the longest carbon chain so that the main functional group has the lowest number
    4
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20
Q

Explain the tetrahedral shape and bond angle around each carbon atom in alkanes

A

Each carbon atom has four pairs of bonding electrons around it which all repel equally with bond angles of 109.5.

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21
Q

What are the single bonds in alkanes called?

A

Sigma bonds

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22
Q

How are sigma bonds formed?

A

When aromatic orbitals on neighbouring atoms overlap to form a new orbital directly between the bonded atoms.

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23
Q

Describe the bonding in alkanes

A

The C-C and C-H bonds are all single covalent bonds

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24
Q

Do sigma bonds have a high/low bond enthalpy? Why?

A

They have a high bond enthalpy and are the strongest type of covalent bond because the bonded atoms are free to rotate around the sigma bond.

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25
Q

Why do sigma bonds have a high bond enthalpy?

A

The high electron density between the nuclei means there is a strong electrostatic attraction between the nuclei and the shared pair of electrons.

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26
Q

Explain why alkanes have a high/low reactivity

A

Alkanes have a low reactivity because the C-C and C-H sigma bonds all have large bond enthalpy making them strong and difficult to break. The bonds are also non-polar and won’t attract to charged particles.

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27
Q

What factors affect the boiling points of alkanes?

A

Size and shape

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28
Q

Explain how size affects the boiling points of alkanes

A

The longer the carbon chain, the more induced dipole-dipole interactions there are because they have a larger molecular surface area so there is more surface contact between the molecules and more electrons to interact>

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29
Q

Why do branched alkanes have a lower boiling point that straight chain alkanes?

A

Branched chain alkanes can’t pack closely together and they have smaller molecular surface areas so induced dipole-dipole interactions are reduced.

30
Q

What are the products of complete combustion of alkanes?

A

Carbon dioxide and water

31
Q

Describe the complete combustion of alkanes

A

Smaller alkanes are combusted easier because complete combustion reactions happen between gases so liquid alkanes have to be vaporised first.

32
Q

Why are larger alkanes used as fuel

A

When alkanes burn some energy is used to break the covalent bonds but more energy is released by forming the new product bonds in CO2 and H2O so larger alkanes release more energy than smaller ones.

33
Q

Describe the incomplete combustion of alkanes

A

If there is a short supply of oxygen alkanes will still burn but it will produce carbon monoxide and water.

34
Q

Explain why carbon monoxide is poisonous?

A

It binds to haemoglobin in the blood which prevents the haemoglobin binding to oxygen so less oxygen is transported around the body.

35
Q

Describe heterolytic fission

A

The bond breaks unevenly with one bonded atom receiving both electrons from the bonded pair so two different substances are formed, a cation and anion.

36
Q

What is the general equation for heterolytic fission?

A

XY = X+ +Y-

37
Q

Describe homolytic fission

A

The bond breaks evenly and each bonding atom receives one electron from the bonded pair and to uncharged radicals are formed.

38
Q

What are radicals?

A

Particles that have an unpaired electron.

39
Q

What is the general equation for homolytic fission?

A

XY = X. + Y.

40
Q

What does a curly arrow represent?

A

Describes the movement of an electron pair and can show either heterolytic fission or formation of a covalent bond.

41
Q

What are photochemical reactions?

A

Reactions started by light

42
Q

Describe radical substitution reactions

A

During the formation of haloalkanes a hydrogen atom is substituted by a halogen.

43
Q

What are the three stages of radical substitution?

A
  1. Initiation- radicals are produced
  2. Propagation- radicals are used up and created in a chain reaction
  3. Termination- two radicals are joined to make a stable molecule
44
Q

What are some problems with radical substitution?

A

hfelhghv

45
Q

Define alkene

A

Unsaturated hydrocarbon containing C=C double bonds.

46
Q

What is the general formula of an alkene?

A

CnH2n

47
Q

What is the structure of a double bond?

A

Made up of a sigma bond and a pi bond

48
Q

How is a pi bond formed?

A

Two orbitals overlap sideways, one above and one below the molecular axis because the p orbitals which overlap are dumbbell shaped.

49
Q

Which bond is weaker, sigma or pi? Why?

A

Sigma bonds are weaker because the electron density is spread out above and below the nuclei which means that the electrostatic attraction between the nuclei and shared pair of electrons is weaker so sigma bonds have a low bond enthalpy.

50
Q

Explain the reactivity of alkenes

A

There are two pairs of electrons in the C=C double bond which has a high electron density. Also the sigma bonds sticks out above and below the molecule so are likely to be attacked by electrophiles.

51
Q

What are electrophiles?

A

Electron pair acceptors with low electron densities.

52
Q

Explain the trigonal planar shape in an alkene molecule?

A

The three bonds repel each other as much as possible and arrange themselves into a trigonal planar shape where the atoms attached to each double bond carbon are at the corners of an imaginary equilateral triangle.

53
Q

Define streoisomers

A

Compounds with the same structural formula but with a different arrangement of space.

54
Q

Describe E/Z isomerism

A

When the double bonded carbon atoms each have two different atoms or groups attached to them.

55
Q

What is E isomerism?

A

If the two carbon atoms have their ‘high priority groups’ on opposite sides.

56
Q

What is Z isomerism?

A

If the two carbon atoms have their ‘high priority groups’ on the same side.

57
Q

Describe cis-trans isomerism

A

Where two carbon atoms either side of the double bond have at least one group in common.

58
Q

What is cis isomerism?

A

The one that has the two identical groups on the same side of the C=C double bond.

59
Q

What is trans isomerism?

A

The one that has the two identical groups on opposite sides of the C=C double bond.

60
Q

Describe electrophilic additon reaxtions

A

Two electrons from the C=C bond attack the delta+ X atom creating a new bond between the carbon 1 and the X atom. The X-Y bond breaks (heterolytic fission) and the electrons from the bond are taken by the Y atom to form a negative ion with a lone pair of electrons. Carbon 2 is left electron deficient because when the double bond broke carbon 1 took the electrons to form a bond with the X atom which left carbo 2 as a positively charged carbocation intermediate. The Y- ion then acts as a nucleophile attacking the positively charged carbocation intermediate and donating its lone pair of electrons forming a new bond with carbon 2.

61
Q

Define nucleophile

A

An electron pair donor

62
Q

What is the general formula for an electrophilic addition reaction?

A

H2C=CH2 + X-Y = CH2XCH2Y

63
Q

Describe the addition reaction of alkenes with hydrogen in the presence of a catalyst?

A

Produces alkanes

H2C=CH2 + H2 = CH3CH3

64
Q

Describe the addition reaction of alkenes with halogens in the presence of a catalyst?

A

Produces a dihaloalkane

H2C=CH2 + X2 = CH2XCH2X

65
Q

What is the investigation to test for alkenes?

A
  1. Use a pipette to add 2 cm3 of orange bromine water to a test tube.
  2. Use a pipette to add 2 cm3 of your unknown hydrocarbon sample to the same test tube.
  3. Stopper the test tube and shake it
  4. Record any observations in a table of results
66
Q

How can bromine water be used to test for alkenes?

A

If the solution turns colourless this means that bromine is added across the double bond to form a colourless dibromoalkane, which happens by electrophilic addition.

67
Q

Describe the addition reaction of alkenes with steam in the presence of an acid catalyst?

A

Alkenes can be hydrated by steam at 300 c and at a pressure of 60-70 atm using an acid catalyst to form an alcohol.
H2C=CH2(g) + H2O(g) = CH3CH2OH(g)

68
Q

Describe the addition reaction of alkenes with hydrogen halides?

A

Forms a haloalkane

69
Q

What is Markownikoff’s rule

A

If the hydrogen halide adds to a symmetrical alkene like ethene then only one product will form. If it is added to an unsymmetrical alkene, two products will form.

70
Q

fhkfug

A

ihszlrbuh

71
Q

Describe the addition polymerisation of alkenes

A

The double bonds in alkenes can open up and join together to make long chains called polymers.

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