chemistry > topic 15 - transition metals > Flashcards

topic 15 - transition metals Flashcards

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1
Q

what is the definition of a transition metal

A

d-block elements which form 1 or more stable ions with incompletely filled d orbitals

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2
Q

what is the definition of a d-block element

A

elements which have their outermost electron in a d sub shell

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3
Q

which 2 elements are d-block elements but not transition metals

A

zinc
scandium

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4
Q

why are zinc and scandium d block elements but not transition metals

A

zinc and scandium have their outermost electron in a d sub shell
but they don’t form ions with incompletely filled d sub shells

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5
Q

when writing electronic configurations, what is the general rule surrounding the 4s and 3d sub shells
what is the exception

A

-4s sub shell fills and empties before 3d
-except for chromium and copper, 4s sub shell partially fills, so that 3d sub shell can be full

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6
Q

state the properties of transition metals

A

-hard solids
-high melting point and boiling point
-act as catalyst
-form coloured ions and compounds
-form ions with different oxidation numbers
-form ions with incompletely filled d sub shells

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7
Q

what is the electronic configuration for Cu, Cu+, Cu2+, Cr

A

Cu - [Ar] 4s^1 3d^10
Cu+ - [Ar] 3d^10
Cu2+ - [Ar] 3d^9
Cr - [Ar] 4s^1 3d^5

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8
Q

explain why transition metals have variable oxidation numbers

A

-4s sub shells and 3d sub shells have very similar energies
-so there isn’t a big jump between the 2nd and 3rd ionisation energies
-so electrons from 4s and 3d sub shells are available for bonding
-so different numbers of electrons can be lost
E.g. in iron there isn’t a big jump between the 2nd and 3rd ionisation energy
-so the increase in lattice enthalpy released when FeCl3 is formed compensates for the 3 ionisation energies
-so FeCl2 and FeCl3 are commonly made

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9
Q

why is CaCl2 more common than CaCl

A

-when transition metals form compounds, the more energy released, the more energetically stable the compound, so the more likely it will be formed
-this depends on:
-the sum of ionisation energies
-energy released when bonds are formed in the new compound
-the formation of CaCl is only slightly exothermic (release a small amount of energy)
-in CaCl2, more energy is taken in for ionisation energies, but much more lattice energy is released, because there is much stronger electrostatic attraction between Ca2+ and Cl-
-so CaCl2 releases more energy, so is more energetically stable

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10
Q

what is the definition of a complex ion

A

a metal ion at the centre with small molecules or negative ions joined by dative covalent bonds, which has an overall positive or negative charge

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11
Q

what is another name for a dative covalent bond

A

coordinate bond

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12
Q

what is the definition of a ligand

A

a species which uses a lone pair of electrons to form a dative covalent bond with a metal ion

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13
Q

what is the coordinate number

A

number of dative covalent bonds formed around the metal ion in a complex / complex ion

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14
Q

what’s the name in complex for the ligand: water

A

aqua

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15
Q

what’s the name in complex for the ligand: hydroxide

A

hydroxo

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16
Q

what’s the name in complex for the ligand: ammonia

A

ammine

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17
Q

what’s the name in complex for the ligand: chloride

A

chloro

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18
Q

are ions which have completely filled d sub shells or have no electrons in d subshells coloured

A

-ions which have completely filled d sub shells or have no electrons in d subshells are colourless
-because when the d sub shell splits, there won’t be space for a lower energy electron to become excited and move to the higher energy level

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19
Q

explain why are transition metal ions coloured

A

-when the ligand bonds to the metal ion the d sub shell splits
-there is capacity for 2 orbitals (4 electrons) to have a higher energy
-and 3 orbitals (6 electrons) to have a lower energy
-but all the spaces won’t be full as ions with full 3 d subshells aren’t coloured
-one of the electrons from the lower energy level absorbs energy from the EM spectrum (becomes excited) and moves to the higher energy level
-the amount of energy it absorbs depends on the difference in energy between the 2 levels

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20
Q

what 4 factors affect the energy gap between split d-orbitals, and therefore affect the colour of transition metal ions

A

the metal
oxidation number
ligands
co-ordination number

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21
Q

how do you predict the shape of a complex

A

count the number of ligands (co-ordination number), this is the number of bonds the central ion forms
6 ligands = octahedral
4 ligands = tetrahedral
2 ligands = linear

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22
Q

what is the meaning of six-fold coordination

A

complexes in which there are six ligands forming coordinate bonds with the transition metal ion

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23
Q

state the most common ligands in octahedral complexes

A

water
ammonia
hydroxide ion
despite having different numbers of lone pairs, all these ligands use 1 lone pair to form a dative covalent bond with the transition metal ion
they are all relatively the same size

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24
Q

state the most common ligand in tetrahedral complexes

A

chloride
chloride is bigger than water, so fewer ions can fit around the transition metal ion

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25
describe square planar molecules
4 bonds around the central transition metal ion 2 lone pairs of electrons on the transition metal ion the 4 bonds are in the same plane (2 going back 2 going forward) bond angles are all 90 degrees
26
state the complex which is used as a cancer treatment
cis-platin
27
what is the shape of a cis-platin compex
square planar
28
what atoms make up cis-platin
platinum (I) ion in the center 2 ammonia ligands 2 chloride ligands
29
how does cis-platin function as a cancer treatment
the structure of cis-platin allows it to form a bond between the 2 strands of DNA, so they can't unwind for DNA replication, so cancer cells can't divide
30
why is trans-platin not used as a cancer treatment
its different structure means it can't as easily bind to the 2 DNA strands, so it doesn't prevent cancer cells from dividing trans-platin is toxic
31
what is the definition of a monodentate ligand
uses 1 lone pair of electrons to form 1 dative covalent bond with a metal ion
32
what is the definition of a bidentate ligand
the ligand has 2 atoms which each use a lone pair of electrons to form 2 dative covalent bond with a metal ion
33
what is the definition of a multidentate ligand
the ligand has several atoms which each use several lone pairs of electrons to form several dative covalent bond with a metal ion
34
in this ligand exchange equation: water is monodentate and en is a bidentate ligand [Cu(H2O)6]2+ + 3en = [Cu(en)3]2+ + 6H2O has thermodynamic stability increased or decreased
we go from having 4 species to 7 species the system is more disordered entropy change of system increases so products are more stable than reactants
35
explain why breathing in carbon monoxide causes death
-the strength of the dative bond between an oxygen and haemoglobin isn't very strong -carbon monoxide can act as a ligand because there is a lone pair of electrons on the carbon -the dative bond between CO and haemoglobin is much stronger so it doesn't break easily -ligand substitution reaction happens -CO takes the place of O2 -no O2 can be transported around the body
36
state examples of monodentate ligands
water chloride ammonia hydroxide ion
37
state examples of bidentate ligands
1,2-diaminoethane (en) ethanedioate
38
state examples of multidentate ligands
EDTA4-
39
what is the colour of cobalt 2+ ions in solution
pink solution
40
what is the colour of iron 2+ ions in solution
pale green solution
41
what is the colour of iron 3+ ions in solution
yellow-brown solution
42
describe the colour change when NaOH is added to Co2+ solution what is the equation is there any change when excess NaOH is added
pink solution to blue precipitate [Co(H2O)6]2+ + 2OH- = [Co(H2O)4(OH-)2] + 2H2O this is deprotonation / acid base reaction no change when excess NaOH is added
43
describe the colour change when NH3 is added to Co2+ solution what is the equation is there any change when excess NH3 is added
pink solution to blue precipitate [Co(H2O)6]2+ + 2NH3 = [Co(H2O)4(OH-)2] + 2NH4+ this is deprotonation / acid base reaction ligand exchange occurs when excess NH3 is added [Co(H2O)4(OH-)2] + 6NH3 = [Co(NH3)6]2+ + 4H2O + 2OH- blue precipitate dissolves to form a brown solution
44
describe the colour change when HCl is added to Co2+ solution what is the equation
from a pink solution to blue solution [Co(H2O)6]2+ 4Cl- = [CoCl4]2- + 6H2O this is ligand exchange and change in coordination number
45
describe the colour change when NaOH is added to Fe2+ solution what is the equation is there any change when excess NaOH is added
pale green solution to green precipitate [Fe(H20)6]2+ + 2OH- = [Fe(H2O)4(OH)2] + 2H2O deprotonation / acid-base reaction no change when excess NaOH added
46
describe the colour change when NH3 is added to Fe2+ solution what is the equation is there any change when excess NH3 is added
pale green solution to green precipitate [Fe(H20)6]2+ + 2NH3 = [Fe(H2O)4(OH)2] + 2NH4+ deprotonation / acid-base reaction no change when excess NH3 added
47
describe the colour change when NaOH is added to Fe3+ solution what is the equation is there any change when excess NaOH is added
yellow-brown solution to brown precipitate [Fe(H20)6]3+ + 3OH- = [Fe(H2O)3(OH)3] + 3H2O deprotonation / acid-base reaction no change when excess NaOH added
48
describe the colour change when NH3 is added to Fe3+ solution what is the equation is there any change when excess NH3 is added
yellow-brown solution to brown precipitate [Fe(H20)6]3+ + 3NH3 = [Fe(H2O)3(OH)3] + 3H2O deprotonation / acid-base reaction no change when excess NH3 added
49
describe the colour change when NaOH is added to Cu2+ solution what is the equation is there any change when excess NaOH is added
pale blue solution to blue precipitate [Cu(H2O)6]2+ + 2OH- = [Cu(H2O)4(OH)2] + 2H2O deprotonation / acid-base reaction no change when excess NH3 added
50
describe the colour change when NH3 is added to Cu2+ solution what is the equation is there any change when excess NH3 is added
pale blue solution to blue precipitate [Cu(H2O)6]2+ + 2NH3 = [Cu(H2O)4(OH)2] + 2NH4+ deprotonation / acid-base reaction when excess NH3 is added blue precipitate dissolves to form a deep blue solution [Cu(H2O)4(OH)2] + 4NH3 = [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH- ligand exchange
51
describe the colour change when HCl is added to Cu2+ solution what is the equation
pale blue solution to green to yellow a green solution appears temporarily because blue and yellow solutions mix [Cu(H2O)6]2+ + Cl- = [CuCl4]2- + 6H2O ligand exchange
52
why does Cu2+ have a coordination number of 6 with H2O ligands but only 4 with Cl- ligands
chloride ligands are bigger than H2O molecules so only 4 can fit around the copper ion
53
describe the colour change when NaOH is added to Cr3+ solution what is the equation is there any change when excess NaOH is added
green solution to green precipitate [Cr(H2O)6]3+ + 3OH- = [Cr(H2O)3(OH)3] + 3H2O deprotonation / acid-base reaction when excess NaOH is added green precipitate dissolves forming a dark green solution [Cr(H2O)3(OH)3] + OH- = [Cr(H2O)2(OH)4]- + H2O further deprotonation
54
describe the colour change when NH3 is added to Cr3+ solution what is the equation is there any change when excess NH3 is added
green solution to green precipitate [Cr(H2O)6]3+ + 3NH3 = [Cr(H2O)3(OH)3] + 3NH4+ deprotonation when excess NH3 is added green precipitate dissolves to form purple solution [Cr(H2O)3(OH)3] + 6NH3 = [Cr(NH3)6] + 3H2O + 3OH- Ligand exchange
55
describe how the chromate(VI) ion can be obtained from Cr3+ ion solution, what is the equation and colour changes seen
-in an alkaline solution of Cr3+ ions add hydrogen peroxide 2[Cr(OH)6]3- + 3H2O2 = 2CrO4^2- + 2OH- + 8H2O -from green solution (when chromium has oxidation number of 3+) to yellow solution (when chromium has oxidation number of 6+)
56
describe how the dichromate(VI) ion can be obtained from the chromate(VI) ion solution, what is the equation and colour changes seen
-in an acidic solution, it goes from yellow to orange 2CrO4^2- + 2H+ = Cr2O7^2- + H2O -this reaction can be reversed by adding alkali
57
Describe how the dichromate(VI) ion is reduced to Cr3+ and then 2+ What colour changes occur and what are the corresponding equations
58
describe how dichromate(VI) ions are reduced into a solution of Cr3+ and Cr2+
-zinc metal is added to an acidic solution of dichromate(VI) ions -reduction occurs -from orange to green, as dichromate(VI) ions turn into Cr3+ Cr2O7^2- + 14H+ + 3Zn = 2Cr3+ + 7H2O + 3Zn2+ -in the same conditions further reduction occurs -from green to blue, as Cr3+ turns into Cr2+ 2Cr3+ + Zn = 2Cr2+ + Zn2+
59
describe how to get a solution of dichromate(VI) ions from a solution of Cr3+ ions
-first make chromate(VI) ions by adding hydrogen peroxide in alkaline conditions -add acid to make dichromate(VI) ions
60
what is the colour and formula of vanadium with an oxidation number of +2
V2+ purple
61
what is the colour and formula of vanadium with an oxidation number of +3
V3+ green
62
what is the colour and formula of vanadium with an oxidation number of +4
VO^2+ blue
63
what is the colour and formula of vanadium with an oxidation number of +5
VO2^+ yellow
64
why does the substitution of a monodentate ligand for a bidentate ligand make a more stable complex ion
-there is a large positive increase in delta S system -because there are more product molecules than reactant molecules -so the system is more disordered, so entropy increases
65
what is a heterogenous catalyst
the catalyst is in a different state to that of the reactants the reaction occurs on the surface of the solid catalyst
66
what is the catalyst used in the contact process what type of catalyst is it
V2O5 heterogenous catalyst
67
describe how V2O5 is used as a heterogenous catalyst in the contact process
-in the contact process sulfur dioxide is turned into sulfur trioxide by passing the gases over a catalyst of V2O5 2SO2 + O2 = 2SO3 -the reactants and products are gaseous while V2O5 is solid
68
explain the surface adsorption theory in the contact process
-SO2 adsorbs onto surface of V2O5 solid catalyst -bonds in SO2 weaken -redox reaction occurs V2O5 + SO2 = V2O4 + SO3 -oxidation number of vanadium decreases from +5 to +4 -SO3 desorbs -O2 adsorbs onto surface of V2O4, redox reaction occurs -original catalyst is regenerated as oxidation number of vanadium increases from +4 to +5
69
explain what occurs inside a catalytic converter
-CO + NO adsorb onto surface of platinum -bonds weaken, CO + NO react together -CO2 + N2 desorb from surface of catalyst 2CO + 2NO = 2CO2 + N2
70
what is a homogenous catalyst
the catalyst is in the same state as that of the reactants and products involved formation of an intermediate species
71
explain the use of a solution of Fe2+ ions as a homogenous catalyst in the reaction between S2O8^-2 + I-
-Fe2+ is attracted to S2O8^2- Fe2+ + S2O8^2- = 2SO4^2- + 2Fe3+ -Fe3+ is attracted to I- Fe3+ + I- = Fe2+ + I2 -the catalyst is regenerated -the overall reaction is S2O8^2- + 2I- = I2 + 2SO4^2-
72
explain the use of a solution of Fe3+ ions as a homogenous catalyst in the reaction between S2O8^-2 + I-
-Fe3+ is attracted to I- Fe3+ + I- = Fe2+ + I2 -Fe2+ is attracted to S2O8^2- Fe2+ + S2O8^2- = 2SO4^2- + 2Fe3+ -the catalyst is regenerated -the overall reaction is S2O8^2- + 2I- = I2 + 2SO4^2-
73
in the reaction between S2O8^-2 + I- why do the reactants not directly react together
both reactants are negatively charged so repel each other
74
why is the reaction between MnO4^- + C2O4^2- called an autocatalysis reaction
2MnO4^- + 16H+ + 5C2O4^2- = 2Mn^2+ + 8H2O = 10 CO2 Mn^2+ (a product) acts as a catalyst MnO4^- + 8H+ + 5Mn^2+ = Mn2+ + 4H2O + 5Mn3+ Mn3+ acts as an intermediate C2O4^2 + 2Mn3+ = 2CO2 + 2Mn2+ the Mn2+ catalyst is regenerated
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