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Transition metals Flashcards

1
Q

why do transition metals have unique characteristics?

A

due to their incomplete d-subshell in atoms or ions

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2
Q

what are the 4 characteristic properties of transition metals?

A

formation of coloured ions
complex formation
variable oxidation states
catalytic activity

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3
Q

what is a ligand?

A

a molecule or ion that forms a co-ordinate bond with a transition metal by donating an electron pair

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4
Q

what is a complex?

A

a central metal atom or ion surrounded by ligands coordinately bonded

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5
Q

what is the coordination number?

A

the number of co-ordinate bonds to the central metal atom or ion

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6
Q

the 3 monodentate ligands to know

A

H2O
NH3
Cl-

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7
Q

what is similar about the ligands NH3 and H2O? what does this mean when they are exchanged?

A

they are a similar size and uncharged so when they are exchanged there is no change in coordination number

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8
Q

how is the Cl- ligand different from NH3 and H2O?

A

it is larger and charged

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9
Q

does ligand substitution have to be complete?

A

no it can be partial

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10
Q

what is a bidentate ligand?

A

each bidentate ligand can form 2 coordinate bonds because they have 2 lone pairs

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11
Q

which elements are NOT transition metals?

A

Sc and Zn

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12
Q

what type of ligand is EDTA4-?

A

multidentate

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13
Q

what type of ligand is C2O42-?

A

bidentate

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14
Q

what is haem?

A

an iron (II) complex with a multidentate ligand

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15
Q

how is oxygen transported in the blood?

A

it forms a coordinate bond to Fe(II) in haemoglobin

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16
Q

why is carbon monoxide toxic?

A

it replaces the oxygen that is coordinately bonded to Fe(II) in haemoglobinso oxygen cannot be transported around the body

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17
Q

what is the chelate effect?

A

when monodentate ligands are replaced with bidentate or multidentate ligands, the number of particles in solution increases so the entropy is greater (because there his more disorder) and the complex is more stable

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18
Q

what does a positive entropy change result in?

A

a more stable complex (so it is favourable)

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19
Q

why is the enthalpy change often very small when a ligand substitution reaction occurs?

A

the strength of the bonds broken is very similar to this being made so the same amount of energy is required and released

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20
Q

bond breaking

A

requires energy

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21
Q

bond forming

A

gives out energy

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22
Q

what shape complexes do small ligands (e.g. H2O, NH3) form?

A

octahedral (6 coordinate bonds)

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23
Q

what isomerism do octahedral complexes show with monodentate ligands?

A

cis-trans

cis = Z
trans = E

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24
Q

what isomerism do octahedral complexes show with bidentate ligands?

A

optical isomerism

25
what shape complexes do large ligands (e.g.Cl-) form?
tetrahedral (4 coordinate bonds)
26
what isomerism do square planar complexes show?
cis-trans
27
what isomer (cis or trans) is cisplatin
cis
28
what linear complex does Ag+ form that is used in Tollens reagent?
[Ag(NH3)2]+
29
how can transition metals be identified?
by their colour
30
why are transition metals coloured?
some of the wavelengths of visible light are absorbed and d electrons move from the ground state to an excited state the other wavelengths of light are reflected
31
do we see reflected or absorbed light?
reflected
32
equation for the energy difference between the ground state and the excited state of the d electrons
∆E = hν = hc/λ h = planks constant v = frequency of light absorbed c = speed of light λ = wavelength of light absorbed
33
what causes the different colours of the transition metals
different ligands different oxidation states change in coordination number
34
what can be used to determine the concentration of coloured ions in solution?
a simple colorimeter
35
what is the redox potential for a transition metal ion changing from a higher to a lower oxidation state influenced by?
pH and the ligand (the environment it is in)
36
what does redox potential tell us?
how easy an atom or ion is reduced to a lower oxidation state (same as electrode potentials!)
37
larger redox potential = ?
larger redox potential = more easily reduced
38
colour of VO2 + (+5 oxidation state)
yellow
39
colour of VO 2+ (+4 oxidation state)
blue
40
colour of V 3+ (+3 oxidation state)
green
41
colour of V 2+ (+2 oxidation state)
violet
42
how can vanadium (V) ions be reduced?
adding them to zinc metal in acidic solution
43
MnO4- : Fe2+
1:5
44
MnO4- : C2O42-
2:5
45
what types of catalysts can transition metals act as?
homogenous and heterogenous
46
what catalyst is used in the Contact process? what type of catalyst is it?
V2O5 heterogeneous catalyst
47
what catalyst is used in the Haber process? what type of catalyst is it?
Fe heterogeneous catalyst
48
where does the reaction occur in heterogeneous catalysts?
at the active sites on the surface
49
what happens when catalysts and reactants are in the same phase?
the reaction proceeds through an intermediate species
50
what is the bad thing that can happen to heterogeneous catalysts?
they can become poisoned by impurities that block the active sites which prevents adsorption and results in reduced efficiency
51
give 2 equations to show how V2O5 acts as a catalyst (in the Contact process)
V2O5 + SO2 --> V2O4 + SO3 V2O4 + 1/2O2 --> V2O5
52
why do transition metals make good catalysts?
due to their variable oxidation states
53
what does the strength off adsorption depend on?
the type of catalyst
54
which are the 3 best catalysts?
iron, cobalt and nickel
55
what catalyses the reaction between S2O82- ions and I- ions? what type of catalyst is it? why is it needed?
Fe2+ homogeneous catalyst the ions naturally repel and so would not react without it
56
what is autocatalysis?
when one of the products of a reaction acts as a catalyst for it e.g. M2+ are an autocatalyst of the reaction between MnO4- and C2O42- ions
57
how does a solid catalyst work?
by adsorbing molecules onto its active site which increases the proximity of the molecules and weakens the covalent bonds so the reaction occurs more easily and therefore the rate of reaction is increased
58
give 2 equations to show how Fe2+ acts as a catalyst (in the reaction between S2O82- and I- ions)
S2O82-+ 2Fe2+ --> 2Fe3+ + 2SO42- 2Fe3+ + 2I- --> 2Fe2+ + I2

Physical and inorganic chemistry (7 decks)

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