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AQA - A level Chemistry > Transition metals > Flashcards

Transition metals Flashcards

1
Q

What is a transition element?

A
  • element that forms at least one stable ion
  • with partially filled d sub-shell
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2
Q

Why is scandium not a transition metal?

A
  • does not have partially filled d sub-shell
  • only forms one ion Sc3+
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3
Q

Why is zinc not a transition metal?

A
  • full d sub-shell
  • Zn+ = only ion formed
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4
Q

What are the key features of transition elements?

A
  • complex ions formed
  • coloured ions formed
  • catalytic properties
  • variable oxidation states
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5
Q

what is a co-ordinate bond?

A
  • shared pair of electrons
  • both from same atom
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6
Q

what is a ligand?

A
  • ion/molecule with lone pair of e-
  • can form co-ordinate bond with transition metal ion
  • e.g. H2O
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7
Q

what is a bidentate ligand?

A
  • ion/molecule with 2 lone pairs of e-
  • on two different atoms
  • each forms co-ordinate bond with metal ion
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8
Q

what is a co-ordination number?

A

number of bonds a transition metal forms

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9
Q

what is a complex ion?

A

central atom/ion surrounded by ligands

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10
Q

what is the electron configuration of copper?

A

1s2 2s2 2p6 3s2 3p6 3d10 4s1

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11
Q

what is the rule for electron configurations of transition metal ions?

A

First in - First out
4s sub-shell empties first

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12
Q

What are the 3 types of ligands that transition metals can form?

A
  • monodentate = each ligand forms 1 co-ordinate bond
  • bidentate = each ligand forms 2 co-ordinate bonds
  • multidentate = each ligand forms 2 or more co-ordinate bonds
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13
Q

What are the 3 monodentate ligands?

A
  • NH3
  • H2O
  • Cl-
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14
Q

What are the two bidentate ligands?

A
  • Ethane-1,2-diamine OR 1,2-diaminoethane
    H2:N-CH2-CH2-N:H2
  • ethandioate ion
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15
Q

What are the 4 shapes that transition metals form?

A
  • Octahedral
  • Tetrahedral
  • Square planar
  • Linear
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16
Q

What is an example of an octahedral complex?

A
  • [Cu(H2O)6] 2+
  • H2O = no charge
  • overall charge = 2+
  • oxidation state of Cu = 2+
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17
Q

What is an example of a tetrahedral complex?

A
  • [CoCl4] 2-
  • Cl- = 1- charge
  • overall charge - 2-
  • oxidation state of Co = 2+
  • Cl- ions = relatively large
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18
Q

What is an example of a square planar complex?

A
  • [Ni(CN)4] 2-
  • CN = 1- charge
  • overall charge = 2+
  • oxidation state of Ni = 2+
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19
Q

What is an example of a linear complex?

A
  • [Ag(NH3)2] +
  • NH3 = no charge
  • overall charge = 1+
  • oxidation state of Ag = 1+
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20
Q

What is an example of a bidentate octahedral complex?

A
  • [Ni(NH2CH2CH2NH2)3] 2+
  • oxidation state of Ni = 2+
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21
Q

Copper(I) iodide is a white solid. Explain why copper(I) iodide is white

A
  • Full (3)d (sub)shell or (3)d10
  • No (d-d) transitions possible/ cannot absorb visible/white light
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22
Q

[EDTA] 4-

A
  • hexadentate ligand
  • can form 6 coordinate bonds
  • 2 from N atoms
  • 4 from O- atoms
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23
Q

[Cu(H2O)6]2+ —-> [Cu(H2O)2(NH3)4) 2+

ligand substitution

A

[Cu(H2O)6]2+ + 4NH3 —> [Cu(H2O)2(NH3)4] 2+ + 4H2O

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24
Q

ligand substitution with [Cu(H2O)6]2+ and CN

A

[Cu(H2O)6]2+ + CN —> [Cu(H2O)5 CN]+ + H2O

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25
Q

what is the chelate effect

A
  • mono dentate ligand
  • replaced by bidentate/multidentate ligand
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26
Q

[Cu(H2O)6]2+ and NH2CH2CH2NH2 chelate effect

A

[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6H2O

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27
Q

[Cu(H2O)6]2+ and NH2CH2CH2NH2 chelate effect

describe entropy change in this reaction

A

[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6H2O

  • 4 moles on left
  • 7 moles on right
  • increase in entropy
  • thermodynamically more favourable
  • large increase in entropy = chelate effect
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28
Q

[Co(NH3)6] 2+ and EDTA 4-
chelate effect

A

[Co(NH3)6] 2+ + EDTA 4- —> [CoEDTA] 2- + 6NH3

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29
Q

[Co(NH3)6] 2+ and EDTA 4-
chelate effect

describe entropy change

A

[Co(NH3)6] 2+ + EDTA 4- —> [CoEDTA] 2- + 6NH3

  • 2 moles on left
  • 7 moles on right
  • large increase in entropy
  • thermodynamically favourable
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30
Q

[Cu(NH3)6] 2+ + 3H2NCH2CH2NH2 —> [Cu(H2NCH2CH2NH2)3] 2+ + 6NH3

explain why this reaction is feasible

A
  • enthalpy change = 0
  • same number of Cu-N bonds broken and made
  • 7 molecules produced from 4 molecules
  • large increase in entropy
  • delta G will be negative
  • so reaction is feasible
31
Q

[Cu(H2O)6] 2+ + 4Cl- —>

A

[CuCl4] 2- + 6H2O

32
Q

Haemoglobin

A
  • 4 co-ordinate bonds between Fe2+ N atoms in the haem structure
  • 1 co-ordinate bond with globin (protein)
  • 1 co-ordinate bond between O2 and Fe2+
  • O2 forms a co-ordinate bond to Fe2+ in haemoglobin enabling oxygen to be transported in the blood
  • CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin.
    This prevents O2 from bonding to the Fe2+, causing suffocation
33
Q

2 types of isomerism shown by transition metals

A
  • stereoisomerism
  • optical isomerism
34
Q

stereoisomerism

A

same structural formula but different arrangement of carbon atoms in space

35
Q

cis/trans isomerism

A
  • 4 of one type of ligand
  • 2 of another
  • octahedral complexes
  • 2 ligands 180 degrees opposite eo = trans isomerism
  • 2 ligands 90 degrees next to eo = cis isomerism
36
Q

example of octahedral cis/trans isomerism

A

[CoCl2(NH3)4] +

37
Q

example of square planar cis/trams isomerism

A

[PtCl2(NH3)2]

38
Q

cisplatin

A
  • cis isomer of [PtCl2(NH3)2]
  • effective anti cancer drug
  • binds to DNA in cells and stops replication
  • two Cl- ions substituted for 2 N atoms on adjacent guanine bases
39
Q

example of bidentate cis/trans isomerism

A

[Cr(H2O)2(C2O4)2] -
oxidation state of Cr = +3
co-ordination number = 6

40
Q

cis isomer of [Cr(H2O)2(C2O4)2] - also displays

A

optical isomerism

41
Q

optical isomerism

A
  • occurs with at least 2 bidentate ligands
  • 2 bidentate ligands and 2 mono dentate = structure has to be cis to be optical
42
Q

ROY G BIV

A

ROY = low energy
BIV = high energy

43
Q

why does KMnO4 appear purple

A
  • contains Mn2+
  • absorbs yellow and green
  • remaining colours reflected
44
Q

why does CuSO4 appear blue

A
  • absorbs ROYG
  • remaining colours make it appear blue
45
Q

why are transition metals coloured

A

partially filled d-sub shells

46
Q

ground state

A

all d orbitals are of equal energy

47
Q

when transition metal moves from lower energy orbital to higher energy orbital

A
  • energy taken from white light
  • absorbed light is missing
  • reflected light gives compound colour
48
Q

frequency of light equation

A

energy change (joules) = Planck constant x frequency of light (Hz)

49
Q

wavelength of light equation

A

energy change (joules) = Planck constant x (speed of light/wavelength of light)

50
Q

if transition metal has large change in energy

A
  • high energy light BIV absorbed to excite electrons
  • ROY reflected
  • compound will look red/orange
51
Q

if transition metal has low change in energy

A
  • low energy light ROY absorbed to excite electrons
  • BIV reflected
  • compound will appear blue/purple
52
Q

change in energy leading change in colour means

A

LOCoS
- change in ligands
- change in oxidation states
- change in co-ordination number
- change in shape of complex

53
Q

[VO2(H2O)4]+ colour

A

oxidation state +5
(VO2) + = yellow

54
Q

[VO(H2O)5]2+ colour

A

oxidation state +4
VO2+ = blue

55
Q

[V(H2O)6]3+ colour

A

oxidation state +3
V3+ = green

56
Q

[V(H2O)6]2+ colour

A

oxidation state +2
V2+ = violet

57
Q

transmittance readings

A

1.0 = all light passed through none absorbed
0.5 = some light passed through some absorbed
0.0 = all light absorbed by transition metal compound

58
Q

to find unknown concentration of sample from calibration curve

A
  • measure absorbance for a range of known concentrations
  • plot graph of absorbance against concentration
  • read value of concentration for the measured absorbance from the graph
59
Q

what is a catalyst

A

chemical/substance that speeds up rate of reaction without being used up

60
Q

how do catalysts work

A

provides alternative pathway with lower activation energy

61
Q

heterogenous catalyst

A

catalyst in different phase to reactants

62
Q

homogenous catalyst

A

catalyst in same phase as reactants

63
Q

heterogeneous catalysis process

A
  • reactants adsorb onto surface of catalyst on an active site
  • reaction occurs on the surface of the catalyst
  • products desorb from surface of catalyst
64
Q

making catalysts efficient

A
  • increase surface area
  • spread catalyst over an inert support medium
65
Q

catalyst poisoning

A
  • impurities can block active sites
  • prevents reactants adsorbing
  • purifying reactants to prevent poisoning
66
Q

heterogenous catalyst example haber process

A

N2 (g) + 3H2 (g) —-> 2NH3 (g)
catalysed by SOLID IRON

67
Q

heterogeneous catalyst example contact process
catalyst V2O5
sulphuric acid made

A

step 1
SO2 (g) + V2O5 (s) —> SO3 (g) + V2O4 (s)

step 2
2V2O4 (s) + O2 (g) —> 2V2O5 (s)

overall reaction
2SO2 (g) + O2 (g) —> 2SO3 (g)
sulfuric acid then made when SO3 reacts with H2O

68
Q

heterogenous catalyst manufacture with methanol

A

step 1
CH4 (g) + H2O (g) —> CO (g) + 3H2 (g)

step 2
CO (g) + 2H2 (g) —> CH3OH
catalysed by chromium oxide Cr2O3

69
Q

why do transition metals act as catalysts

A

they have variable oxidation states

70
Q

homogenous catalysts

A

uncatalysed reaction
S2O8 2- (aq) + 2I- (aq) —> 2SO4 2- (aq) + I2 (aq)
high activation energy due to 2 negative ions repelling eo

step 1
S2O8 2- (aq) + 2Fe 2+(aq) —> 2SO4 2- (aq) + 2 Fe 3+ (aq)

step 2
2Fe 3+ (aq) + 2I- (aq) —> I2 (aq) + 2Fe 2+ (aq)

Fe2+ catalyst regenerated in second step

71
Q

autocatalysis

A
  • example of homogenous catalyst
  • when one of the products of the reaction catalyses the reaction
72
Q

autocatalysis

A

uncatalysed reaction:
2MnO4- + 16H+ + 5C2O4 2- —> 2Mn2+ + 8H2O + 10CO2

step 1:
4Mn2+ + MnO4 - + 8H+ —> 5Mn3+ + 4H2O

step 2:
2Mn3+ + C2O4 2- —> 2Mn2+ + 2CO2

73
Q

autocatalysis - why is initial rate of reaction slow

A
  • both ions negative so they repel
  • high activation energy
74
Q

autocatalysis colour change

A

purple to clear

AQA - A level Chemistry (25 decks)

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