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Transcript of 1 The d-Block Elements. 2 Introduction d-block elements locate between the s-block and p-block ...
1
The The dd-Block Elements-Block Elements
2
IntroductionIntroduction
• d-block elements
locate between the s-block andp-block
known as transition elements
occur in the fourth and subsequent periods of the Periodic Table
3
period 4
period 5
period 6
period 7
d-block elements
4
IntroductionIntroduction
Transition elements are elements that contain an incomplete d sub-shell (i.e. d1 to d9) in at least one of the oxidation states of their compounds.
3d0
3d10
5
IntroductionIntroduction
Sc and Zn are not transition elements because
They form compounds with only one oxidation state in which the d sub-shell are NOT imcomplete.
Sc Sc3+ 3d0 Zn Zn2+ 3d10
6
IntroductionIntroduction
Cu
Cu+ 3d10 not transitional Cu2+ 3d9 transitional
7
The first transition series
the first horizontal row of the d-block elements
8
Characteristics of transition elements
(d-block metals vs s-block metals)
1. Physical properties vary slightly with atomic number across the series (cf. s-block and p-block elements)
2. Higher m.p./b.p./density/hardness than s-block elements of the same periods.
3. Variable oxidation states(cf. fixed oxidation states of s-block metals)
9
Characteristics of transition elements
4. Formation of coloured compounds/ions(cf. colourless ions of s-block elements)
5. Formation of complexes
6. Catalytic properties
10
The building up of electronic configurations of elements follow:
Aufbau principle
Pauli exclusion principle
Hund’s rule
Electronic ConfigurationsElectronic Configurations
11
• 3d and 4s sub-shells are very close to each other in energy.
• Relative energy of electrons in sub-shells depends on the effective nuclear charge they experience.
• Electrons enter 4s sub-shell first
• Electrons leave 4s sub-shell first
Electronic ConfigurationsElectronic Configurations
12
Cu Cu2+
Relative energy levels of orbitals in atom and in ion
13
• Valence electrons in the inner 3d orbitals
Electronic ConfigurationsElectronic Configurations
• Examples:
The electronic configuration of scandium:
1s22s22p63s23p63d14s2
The electronic configuration of zinc: 1s22s22p63s23p63d104s2
14
Element Atomic number Electronic configuration
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
21
22
23
24
25
26
27
28
29
30
[Ar] 3d 14s2
[Ar] 3d 24s2
[Ar] 3d 34s2
[Ar] 3d 54s1
[Ar] 3d 54s2
[Ar] 3d 64s2
[Ar] 3d 74s2
[Ar] 3d 84s2
[Ar] 3d 104s1
[Ar] 3d 104s2
Electronic configurations of the first series of the d-block elements
15
• A half-filled or fully-filled d sub-shell
has extra stability
16
dd -Block Elements as Metals-Block Elements as Metals
Physical properties of d-Block elements :
good conductors of heat and electricity
hard and strong
malleable and ductile
• d-Block elements are typical metals
17
dd -Block Elements as Metals-Block Elements as Metals
• Physical properties of d-Block elements:
• Exceptions : Mercury
low melting point
liquid at room temperature and pressure
lustrous
high melting points and boiling points
18
dd -Block Elements as Metals-Block Elements as Metals
• d-block elements
extremely useful as construction materials
strong and unreactive
19
dd -Block Elements as Metals-Block Elements as Metals
used for construction and making machinery nowadays
abundant
easy to extract
• Iron
cheap
20
dd -Block Elements as Metals-Block Elements as Metals
• Iron
corrodes easily
often combined with other elements to form steel
harder and more resistant to corrosion
21
dd -Block Elements as Metals-Block Elements as Metals
• Titanium
used to make aircraft and space shuttles
expensive
Corrosion resistant, light, strong and withstand large temperature changes
22
dd -Block Elements as Metals-Block Elements as Metals
• The similar atomic radii of the transition metals facilitate the formation of substitutional alloys
the atoms of one element to replace those of another
element
modify their solid structures and physical properties
23
dd -Block Elements as Metals-Block Elements as Metals
• Manganese
confers hardness & wearing resistance to its alloys
e.g. duralumin : alloy of Al with Mn/Mg/Cu
• Chromium
confers inertness to stainless steel
24
Atomic Radii and Ionic RadiiAtomic Radii and Ionic Radii
• Two features can be observed:
1. The d-block elements have smaller atomic radii than the s-block
elements2. The atomic radii of the d-block
elements do not show much variation across the series
25
Variation in atomic radius of the first 36 elements
Atomic Radii and Ionic RadiiAtomic Radii and Ionic Radii
26
27
28
(i) Nuclear charge
(ii) Shielding effect (repulsion between e-)
(i) > (ii)
(i) (ii)
(ii) > (i)
On moving across the Period,
29
• At the beginning of the series
atomic number
effective nuclear charge
the electron clouds are pulled closer to the nucleus
atomic size
Atomic Radii and Ionic RadiiAtomic Radii and Ionic Radii
30
• In the middle of the series
the effective nuclear charge experienced by 4s electrons
increases very slowly
only a slow decrease in atomic radius in this region
more electrons enter the inner3d sub-shell
The inner 3d electrons shield the outer 4s electrons
effectively
31
• At the end of the series
the screening and repulsive effects of the electrons in the 3d sub- shell become even stronger
Atomic size
Atomic Radii and Ionic RadiiAtomic Radii and Ionic Radii
32
• Many of the differences in physical and chemical properties between the d-block and s-block elements
explained in terms of their differences in electronic configurations and atomic radii
Comparison of Some Physical Comparison of Some Physical and Chemical Properties and Chemical Properties between the between the dd-Block and -Block and ss-Block -Block ElementsElements
33
1. 1. DensityDensity
Densities (in g cm–3) of the s-block elements and the first series of the d-block elements at
20C
34
• d-block > s-block
the atoms of the d-block elements 1. are generally smaller in size
2. are more closely packed
(fcc/hcp vs bcc in group 1)
3. have higher relative atomic masses
1. 1. DensityDensity
35
• The densities
generally increase across the first series of the d-block elements
1. general decrease in atomic radius across the
series
2. general increase in atomic mass across the series
1. 1. DensityDensity
36
2. 2. Ionization Ionization
EnthalpyEnthalpy
ElementIonization enthalpy (kJ mol–1)
1st 2nd 3rd 4th
K
Ca
418
590
3 070
1 150
4 600
4 940
5 860
6 480
Sc
Ti
V
Cr
632
661
648
653
1 240
1 310
1 370
1 590
2 390
2 720
2 870
2 990
7 110
4 170
4 600
4 770
K Ca (sharp ) ; Ca Sc (slight )
37
2. 2. Ionization Ionization
EnthalpyEnthalpy
ElementIonization enthalpy (kJ mol–1)
1st 2nd 3rd 4th
Cr
Mn
Fe
Co
Ni
Cu
Zn
653
716
762
757
736
745
908
1 590
1 510
1 560
1 640
1 750
1 960
1 730
2 990
3 250
2 960
3 230
3 390
3 550
3 828
4 770
5 190
5 400
5 100
5 400
5 690
5 980
Sc Cu (slight ) ; Cu Zn (sharp )
38
• The first ionization enthalpies of thed-block elements
greater than those of the s-block elements in the same period of
the Periodic Table
1. The atoms of the d-block elements are smaller in size
2. greater effective nuclear charges
2. 2. Ionization Ionization
EnthalpyEnthalpy
39
Sharp across periods 1, 2 and 3
Slight across the transition series
40
• Going across the first transition series
the nuclear charge of the elements increases
additional electrons are added to the ‘inner’ 3d sub-shell
2. 2. Ionization Ionization
EnthalpyEnthalpy
41
• The screening effect of the additional3d electrons is significant
2. 2. Ionization Ionization
EnthalpyEnthalpy
• The effective nuclear charge experienced by the 4s electrons increases very slightly across the series• For 2nd, 3rd, 4th… ionization enthalpies,
slight and gradual across the series are observed.
42
Electron has to be removed from completely filled 3p subshell
3d5
3d5
3d5
3d10
d10/s2Cr+
Mn2
+
Fe3+
43
• The first few successive ionization enthalpies for the d-block elements
do not show dramatic changes
4s and 3d energy levels are close to each other
2. 2. Ionization Ionization
EnthalpyEnthalpy
44
3. 3. Melting Points and Melting Points and
HardnessHardness
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
d-block >> s-block
1. both 4s and 3d e- are involved in the formation of metal bonds
2. d-block atoms are smaller
45
3. 3. Melting Points and Melting Points and
HardnessHardnessK has an exceptionally small m.p. because it has an more open b.c.c. structure.
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
46
Unpaired electrons are relatively more involved in the sea of electrons
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
47
3d 4s
Sc
Ti
V
1.m.p. from Sc to V due to the of unpaired d-electrons (from d1 to d3)
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
48
2.m.p. from Fe to Zn due to the of unpaired d-electrons (from 4 to 0)
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
3d 4s
Fe
Co
Ni
49
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
3. Cr has the highest no. of unpaired electrons but its m.p. is lower than V.
3d 4s
Cr
It is because the electrons in the half-filled d-subshell are relatively less involved in the sea of electrons.
50
Sc Ti V Cr Mn Fe Co Ni Cu Zn
1541 1668 1910 1907 1246 1538 1495 1455 1084 419
4. Mn has an exceptionally low m.p. because it has the very open cubic structure.
Why is Hg a liquid at room conditions ?
All 5d and 6s electrons are paired up and the size of the atoms is much larger than that of Zn.
51
• The metallic bonds of the d-block elements are stronger than those of the s-block elements
much harder than the s-block elements
3. 3. Melting Points and Melting Points and
HardnessHardness• The hardness of a metal depends on
the strength of the metallic bonds
52
Mohs scale : - A measure of hardness
Talc Diamond
0 10 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn
0.5 1.5 3.0 4.5 6.1 9.0 5.0 4.5 -- -- 2.8 2.5
53
• In general, the s-block elements
react vigorously with water to form metal hydroxides and hydrogen
4. 4. Reaction with WaterReaction with Water
• The d-block elements
react very slowly with cold water
react with steam to give metal oxides and hydrogen
54
4. 4. Reaction with WaterReaction with Water
2K(s) + 2H2O(l) 2KOH(aq) + H2(g)2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g)Zn(s) + H2O(g) ZnO(s) + H2(g)
3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
55
d-block compounds vs s-block compoundsA Summary : -
Ions of d-block metals have higher charge density
more polarizing
1. more covalent in nature
2. less soluble in water
3. less basic (more acidic)
Basicity : Fe(OH)3 < Fe(OH)2 << NaOH
Charge density : Fe3+ > Fe2+ > Na+
56
4. less thermally stable e.g. CuCO3 << Na2CO3
5. tend to exist as hydrated salts
e.g. CuSO4.5H2O, CoCl2.2H2O
6. hydrated ions undergo hydrolysis more easily
e.g. [Fe(H2O)6]3+(aq) + H2O [Fe(OH)(H2O)5]2+(aq) + H3O+
d-block compounds vs s-block compoundsA Summary : -
acidic
57
• One of the most striking properties
variable oxidation states
Variable Oxidation StatesVariable Oxidation States
• The 3d and 4s electrons are
in similar energy levels
available for bonding
58
• Elements of the first transition series
form ions of roughly the same stability by losing different
numbers of the 3d and 4s electrons
Variable Oxidation StatesVariable Oxidation States
59
Oxidation
statesOxides / Chloride
+1Cu2O
Cu2Cl2
+2TiO VO CrO MnO FeO CoO NiO CuO ZnO
TiCl2 VCl2 CrCl2 MnCl2 FeCl2 CoCl2 NiCl2 CuCl2 ZnCl2
+3Sc2O3 Ti2O3 V2O3 Cr2O3 Mn2O3 Fe2O3 Ni2O3 • xH2O
ScCl3 TiCl3 VCl3 CrCl3 MnCl3 FeCl3
+4TiO2 VO2 MnO2
TiCl4 VCl4 CrCl4
+5 V2O5
+6 CrO3
+7 Mn2O7
Oxidation states of the elements of the first transition series in their oxides and chlorides
60
Oxidation states of the elements of the first transition series in their compounds
Element Possible oxidation state
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
Element Possible oxidation state
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
+3
+1 +2 +3 +4
+1 +2 +3 +4 +5
+1 +2 +3 +4 +5 +6
+1 +2 +3 +4 +5 +6 +7
+1 +2 +3 +4 +5 +6
+1 +2 +3 +4 +5
+1 +2 +3 +4 +5
+1 +2 +3
+2
61
1. Scandium and zinc do not exhibit variable oxidation states
• Scandium of the oxidation state +3
the stable electronic configuration of argon (i.e. 1s22s22p63s23p6)• Zinc of the oxidation state +2
the stable electronic configuration of [Ar] 3d10
62
2. (a) All elements of the first transition series (except Sc) can show an oxidation state of +2
(b) All elements of the first transition series (except Zn) can show an oxidation state of +3
63
3. Manganese has the highest oxidation state +7
E.g. MnO4-, Mn2O7
Mn7+ ions do not exist.
64
The +7 state of Mn does not mean that all 3d and 4s electrons are removed from Mn to give Mn7+.
Instead, Mn forms covalent bonds with oxygen atoms by making use of its half filled orbitals
Mn
O
OO
O-
65
Draw the structure of Mn2O7
Mn
O
OO
OMn
O
OO
66
3. Manganese has the highest oxidation state +7
• The highest possible oxidation state
= the total no. of the 3d and 4s electrons
inner electrons (3s, 3p…) are not involved in covalent bond
formation
67
4. For elements after manganese, there is a reduction in the number of possible oxidation states
• The 3d electrons are held more firmly
the decrease in the number of unpaired electrons
the increase in nuclear charge
68
Stability : - Mn2+(aq) > Mn3+(aq)
[Ar] 3d5 [Ar] 3d4
5. The relative stability of various oxidation states is correlated with the stability of electronic configurations
ohydrationH : Fe3+ > Fe2+
Major factor
Major factor
Fe3+(aq) > Fe2+
(aq)
[Ar] 3d5 [Ar] 3d6
69
Stability : -Zn2+(aq) > Zn+
(aq)
[Ar] 3d10 [Ar] 3d104s1
5. The relative stability of various oxidation states is correlated with the stability of electronic configurations
ohydrationH : Zn2+ > Zn+Major factor
70
• The compounds of vanadium, vanadium
oxidation states of +2, +3, +4 and +5
forms ions of different oxidation states
show distinctive colours in aqueous solutions
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
71
Ion
Oxidation state
of vanadium in
the ion
Colour in
aqueous
solution
V2+(aq)
V3+(aq)
VO2+(aq)
VO2+(aq)
+2
+3
+4
+5
Violet
Green
Blue
Yellow
Colours of aqueous ions of vanadium of different oxidation states
72
• In an acidic medium
the vanadium(V) state usually occurs in the form of VO2
+
(aq) dioxovanadium(V) ion
the vanadium(IV) state occurs in the form of VO2+(aq)
oxovanadium(IV) ion
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
73
• In an alkaline medium
the stable form of the vanadium(V) state is
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO3–(aq), metavanadate(V) or
VO43–(aq), orthovanadate(V),
in strongly alkaline medium
74
• Compounds with vanadium in its highest oxidation state (i.e. +5)
strong oxidizing agents
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
75
• Vanadium of its lowest oxidation state(i.e. +2)
in the form of V2+(aq)
strong reducing agent
easily oxidized when exposed to air
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
76
• The most convenient starting material
ammonium metavanadate(V) (NH4VO3)
a white solid
the oxidation state of vanadium is +5
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions• Interconversions of the common oxidation states of vanadium can be carried out readily in the laboratory
77
1. Interconversions of Vanadium(V) species
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO2+(aq) V2O5(s) VO3
(aq) VO4
3(aq)
OH
H+
OH
H+
OH
H+
Yellow orange yellow colourless
Vanadium(V) can exist as cation as well as anion
78
1. Interconversions of Vanadium(V) species
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO2+(aq) V2O5(s) VO3
(aq) VO4
3(aq)
OH
H+
OH
H+
OH
H+
Yellow orange yellow colourless
In acidic medium
In alkaline mediumAmphoteric
79
1. Interconversions of Vanadium(V) species
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO2+(aq) V2O5(s) VO3
(aq) VO4
3(aq)
OH
H+
OH
H+
OH
H+
Yellow orange yellow colourless
In acidic medium
In alkaline mediumAmphotericGive the equation for the conversion : V2O5
VO2+
V2O5(s) + 2H+(aq) 2VO2+(aq) + H2O(l)
80
1. Interconversions of Vanadium(V) species
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO2+(aq) V2O5(s) VO3
(aq) VO4
3(aq)
OH
H+
OH
H+
OH
H+
Yellow orange yellow colourless
In acidic medium
In alkaline mediumAmphotericGive the equation for the conversion : V2O5
VO3
V2O5(s) + 2OH(aq) 2VO3(aq) + H2O(l)
81
1. Interconversions of Vanadium(V) species
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
VO2+(aq) V2O5(s) VO3
(aq) VO4
3(aq)
OH
H+
OH
H+
OH
H+
Yellow orange yellow colourless
In acidic medium
In alkaline medium
Give the equation for the conversion : VO3
VO2+
VO3(aq) + 2H+(aq) VO2
+(aq) + H2O(l)
Amphoteric
82
V5+
H
O
H
H
O
H
H
O
H
H
O
H
VO43(aq) + 8H3O+
8H2O
O
H
H
V5+ ions does not exist in water since it undergoes vigorous hydrolysis to give VO4
3
The reaction is favoured in highly alkaline solution
orthovanadate(V) ion
83
V VO43(aq) orthovanadate(V) ion
Cr CrO42(aq) chromate(VI) ion
Mn MnO4(aq) manganate(VII) ion
Draw the structures of VO43, CrO4
2 and MnO4
O
Cr
OO-
O-
O
Mn
OO
O-
O
V-O
O-O-
84
V5+
H
O
H
H
O
H
H
O
H
H
O
H
VO3(aq) + 6H3O+
6H2O
O
H
H
The reaction is favoured in alkaline solution
VO3 is a polymeric anion like SiO3
2
Metavanadate(V) ion
85
Metavanadate(V) ion, (VO3)nn
86
V5+
H
O
H
H
O
H
H
O
H
H
O
H
VO2+(aq) + 4H3O+
4H2O
O
H
H
The reaction is favoured in acidic solution
87
2. The action of zinc powder and concentrated hydrochloric acid
vanadium(V) ions can be reduced sequentially to vanadium(II) ions
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
88
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversionsVO2
+(aq)
yellow
Zn
conc. HClVO2+(aq) blue
Zn
conc. HCl
V3+(aq) green
Zn
conc. HClV2+(aq)
violet
89
(a)
Colours of aqueous solutions of compounds containing vanadium in four different oxidation
states:(a) +5; (b) +4; (c) +3; (d) +2
(b) (c) (d)
VO2+(aq) VO2+(aq) V3+(aq) V2+(aq)
90
• The feasibility of the changes in oxidation state of vanadium
can be predicted using standard electrode potentials
Half reaction (V)
Zn2+(aq) + 2e– Zn(s)
VO2+(aq) + 2H+(aq) + e– VO2+(aq) + H2O(l)
VO2+(aq) + 2H+(aq) + e– V3+(aq) + H2O(l)
V3+(aq) + e– V2+(aq)
–0.76
+1.00
+0.34
–0.26
91
• Under standard conditions
zinc can reduce
1. VO2+(aq) to VO2+(aq)
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions
> 0
> 0
> 0
2. VO2+(aq) to V3+(aq)
3. V3+(aq) to V2+(aq)
92
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions2 × (VO2+(aq) + 2H+(aq) + e–
VO2+(aq) + H2O(l)) = +1.00 V–) Zn2+(aq) + 2e– Zn(s) = –0.76 V
2VO2+(aq) + Zn(s) + 4H+(aq)
2VO2+(aq) + Zn2+(aq) + 2H2O(l)
= +1.76 V
93
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions2 × (VO2+(aq) + 2H+(aq) + e–
V3+(aq) + H2O(l)) = +0.34 V
–) Zn2+(aq) + 2e– Zn(s) = –0.76 V
2VO2+(aq) + Zn(s) + 4H+(aq)2V3+(aq) + Zn2+(aq) + 2H2O(l)
= +1.10 V
94
1. 1. Variable Oxidation States of Variable Oxidation States of
Vanadium and their Vanadium and their
InterconversionsInterconversions2 × (V3+(aq) + e– V2+(aq)) = –
0.26 V–) Zn2+(aq) + 2e– Zn(s) = –0.76 V
2V3+(aq) + Zn(s) 2V2+(aq) + Zn2+
(aq)
= +0.50 V
95
• Manganese
show oxidation states of +2, +3, +4, +5, +6 and +7 in its compounds
2. 2. Variable Oxidation States of Variable Oxidation States of
Manganese and their Manganese and their
InterconversionsInterconversions
• The most common oxidation states
+2, +4 and +7
96
Ion
Oxidation state of
manganese in the
ion
Colour
Mn2+
Mn(OH)3
Mn3+
MnO2
MnO43
MnO42–
MnO4–
+2
+3
+3
+4
+5
+6
+7
Very pale pink
Dark brown
Red
Black
Bright blue
Green
Purple
Colours of compounds or ions of manganese in different oxidation states
97
(a)
Colours of compounds or ions of manganese in differernt oxidation states: (a) +2; (b) +3; (c) +4
(b) (c)
Mn2+(aq) Mn(OH)3(aq)
MnO2(s)
98
(e)(d)
Colours of compounds or ions of manganese in differernt oxidation states: (d) +6; (e) +7
MnO42–(aq) MnO4
–(aq)
99
• Manganese of the oxidation state +2
the most stable at pH 0
2. 2. Variable Oxidation States of Variable Oxidation States of
Manganese and their Manganese and their
InterconversionsInterconversions
Mn2+Mn3++1.50V Mn
1.18V
MnO4
+1.51V
MnO2
+1.23V
100
Mn(VII)
Explosive on heating and extremely oxidizing2KMnO4 K2MnO4 + MnO2 + O2
heat+7 +6 +42 0
in ON = 2(+2) = +4
in ON = (1) + (3) = 4
101
Mn(VII)
in ON = 6(+2) = +12
in ON = 4(3) = 12
2 0+4+7
4MnO4 + 4H+ 4MnO2 + 2H2O +
3O2
light
The reaction is catalyzed by light
Acidified KMnO4(aq) is stored in amber bottle
102
Oxidizing power of Mn(VII) depends on pH of the solution
In an acidic medium (pH 0)
MnO4–(aq) + 8H+(aq) + 5e– Mn2+(aq) +
4H2O(l) = +1.51 V
In a neutral or alkaline medium (up to pH 14)
MnO4–(aq) + 2H2O(l) + 3e– MnO2(s) +
4OH (aq) = +0.59 V
103
The reaction does not involve H+(aq) nor OH(aq)
Why is the Eo of MnO4 MnO4
2 Eo = +0.56V
not affected by pH ?MnO4
(aq) + e MnO42 Eo = +0.56V
104
MnO4(aq) + e MnO4
2 Eo = +0.56V
When [OH(aq)] > 1M
In an acidic medium (pH 0)
MnO4–(aq) + 8H+(aq) + 5e– Mn2+(aq) +
4H2O(l) = +1.51 V
In a neutral or alkaline medium (up to pH 14)MnO4
–(aq) + 2H2O(l) + 3e– MnO2(s) + 4OH (aq) = +0.59
VUnder what conditions is the following conversion favoured?
105
Predict if Mn(VI) Mn(VII) + Mn(IV) is feasible at (i) pH 0 and (ii) pH 14
At pH 0 (1) 2(3)
3MnO42(aq) + 4H+(aq) 2MnO4
(aq) + MnO2(s) + 2H2O(l)
Eocell = +1.70V (feasible)At pH 14 (2) 2(3)
3MnO42(aq) + 2H2O(l) 2MnO4
(aq) + MnO2(s) + 4OH(aq)
Eocell = +0.04V (much less feasible)
MnO42(aq) + 4H+(aq) + 2e MnO2(s) + 2H2O(l) Eo =
+2.26VMnO4
2(aq) + 2H2O(l) + 2e MnO2(s) + 4OH(aq) Eo = +0.60VMnO4
+ e MnO42 Eo = +0.56V
(1)
(2)
(3)
Mn(VI) is unstable in acidic medium
106
Mn(IV) Oxidizing in acidic medium
MnO2(s) + 4H+(aq) + 2e– Mn2+(aq) + 2H2O(l) = 1.23
V• Used in the laboratory production of
chlorine
MnO2(s) + 4HCl(aq) MnCl2(aq) + 2H2O(l) + Cl2(g)
107
Mn(IV) Reducing in alkaline medium
• Oxidized to Mn(VI) in alkaline medium
2MnO2 + 4OH + O2 2MnO42 + 2H2O
108
MnO2 is oxidized to MnO42 in alkaline medium
2MnO2 + 4OH + O2 2MnO42 + 2H2O
Suggest a scheme to prepare MnO4 from
MnO21. 2MnO2 + 4OH + O2 2MnO42 + 2H2O
2. 3MnO42 + 4H+ 2MnO4
+ MnO2 + 2H2O
3. Filter the resulting mixture to remove MnO2
7B
109
Cu+(aq) + e Cu(s) Eo = +0.52V
Cu2+(aq) + 2e Cu(s) Eo = +0.34V
Cu2+(aq) is more stable than Cu+(aq)
The only copper(I) compounds which can be stable in water are those which are
(i) insoluble (e.g. Cu2O, CuI, CuCl)
(ii) complexed with ligands other than water
e.g. [Cu(NH3)4]+ Cu+(aq) + e Cu(s)Under these conditions, [Cu+
(aq)]
Equil. Position shifts to left
110
Estimation of Cu2+ ions
2Cu2+(aq) + 4I(aq) 2CuI(s) + I2(aq)
I2(aq) + 2S2O32(aq) 2I(aq) + S4O6
2(aq)
unknown
excess white fixed
standard solution
111
• Another striking feature of the d-block elements is the formation of complexes
Formation of ComplexesFormation of Complexes
112
Formation of ComplexesFormation of Complexes
A complex is formed when a central metal atom or ion is surrounded by other molecules or ions which form dative covalent bonds with the central metal atom or ion.
The molecules or ions that donate lone pairs of electrons to form the dative covalent bonds are called ligands.
113
• A ligand
can be an ion or a molecule having at least one lone pair of electrons that can be donated to the central metal atom or ion to form a dative
covalent bond
Formation of ComplexesFormation of Complexes
114
Formation of ComplexesFormation of Complexes
electrically neutral Ni(CO)4
[Co(H2O)6]3+positively charged
[Fe(CN)6]3negatively charged
Complexes can be
115
A co-ordination compound is either
a neutral complex e.g. Ni(CO)4
or made of
a complex ion and another ion
e.g. [Co(H2O)6]Cl3 [Co(H2O)6]3+ + 3Cl
K3[Fe(CN)6] 3K+ + [Fe(CN)6]3
116
Criteria for complex formation
2. High charge density of the central metal ions.
1. Presence of vacant and low-energy 3d, 4s, 4p and 4d orbitals in the metal atoms or ions to accept lone pairs from ligands.
117
Diagrammatic representation of the formation of a complex
118
[Co(H2O)6]2+
Co :
3d 4s 4p 4d
Co2+ :
3d 4s 4p 4d
sp3d2 hybridisation
The six sp3d2 orbitals accept six lone pairs from six H2O.
Arranged octahedrally to minimize repulsion between dative bonds.
119
1. 1. Complexes with Monodentate Complexes with Monodentate
LigandsLigandsA ligand that forms one dative covalent bond only is called a monodentate ligand. • Examples:
neutral CO, H2O, NH3
anionic Cl–, CN–, OH–
120
121
The transition metal ion is the Lewis acid since it accepts lone pairs of electrons from the ligands in forming dative covalent bonds. The ligand is the Lewis base since it donates a lone pair of electrons to the transition metal ion in forming dative covalent bonds.
In the formation of complexes, classify the transition metal ion and the ligand as a Lewis acid or base. Explain your answer briefly.
122
What is the oxidation state of the central metal ?
Cr3+ Zn2+
123
What is the oxidation state of the central metal ?
Co3+
124
What is the oxidation state of the central metal ?
Fe3+ Co2+
125
2. 2. Complexes with Bidentate LigandsComplexes with Bidentate Ligands
A ligand that can form two dative covalent bonds with a metal atom or ion is called a bidentate ligand.
A ligand that can form more than one dative covalent bond with a central metal atom or ion is called a chelating ligand.
126
Ethylenediamine (H2NCH2CH2NH2)
ethylenediamine
Oxalate (C2O42–)
oxalate ion
The term chelate is derived from Greek, meaning ‘claw’.The ligand binds with the metal like the great claw of the lobster.
127
ethylenediamine oxalate ion
128
3. 3. Complexes formed by Multidentate Complexes formed by Multidentate
LigandsLigandsLigands that can form more than two dative covalent bonds to a metal atom or ion are called multidentate ligands. Some ligands can form as many as six bonds to a metal atom or ion. • Example:
ethylenediaminetetraacetic acid (abbreviated as EDTA)
129
ethylenediaminetetraacetate ion
EDTA forms six dative covalent bonds with the metal ion through six atoms giving a very stable complex.
hexadentate ligand
130
EDTA4
Fe2+
[FeEDTA]2
Structure of the complex ion formed by iron(II) ions and EDTA
?2
131
Uses of EDTA
1. Determining concentrations of metal ions by complexometric titrations
e.g. determination of water hardness
2. In chelation therapy for mercury poisoning and lead poisoning
Poisonous Hg2+ and Pb2+ ions are removed by forming stable complexes with EDTA.3. Preparing buffer solutions ( )
4aa K toK1
4. As preservative to prevent catalytic oxidation of food by metal ions.
132
The coordination number of the central metal atom or ion in a complex is the number of dative covalent bonds formed by the central metal atom or ion in a complex.
Complex
The central metal
atom or ion in the
complex
Coordinati
on
number
[Ag(NH3)2]+ Ag+ 2
[Cu(NH3)4]2+ Cu2+ 4
[Fe(CN)6]3– Fe3+ 6
133
4. 4. Nomenclature of Transition Metal Nomenclature of Transition Metal
Complexes with Monodentate Complexes with Monodentate
LigandsLigandsIUPAC conventions
1. (a)For any ionic compound
the cation is named before the anion
(b)If the complex is neutral
the name of the complex is the name of the compound
134
1. (c) In naming a complex (which may be neutral, a cation or an anion)
the ligands are named before the central metal atom or ion
the liqands are named in alphabetical order
(prefixes not counted)(d)The number of each type of ligands are specified by the Greek prefixes1 mono- 2 di 3 tri
4 tetra- 5 penta- 6 hexa-
135
1. (e)The oxidation number of the metal ion in the complex is indicated immediately after the name of the metal using Roman numerals
[CrCl2(H2O)4]Cltetraaquadichlorochromium(III) chloride
[CoCl3(NH3)3]triamminetrichlorocobalt(III)
K3[Fe(CN)6]potassium hexacyanoferrate(III)
136
2. (a)The root names of anionic ligands
always end in “-o”CN–cyano
Cl–
chloro
Br
bromo
I iodo
OH
hydroxo
NO2 nitro
SO42
sulphato
H
hydrido
(b)The names of neutral ligands are the names of the molecules
except NH3, H2O, CO and NO
137
Neutral ligand Name of ligand
Ammonia (NH3)
Water (H2O)
Carbon monoxide (CO)
Nitrogen monoxide (NO)
Ammine
Aqua
Carbonyl
Nitrosyl
138
3. (a)If the complex is anionic
the suffix “-ate” is added to the end of the name of the metal,
followed by the oxidation number of that metal
tetrachlorocuprate(II) ion[CuCl4]2–
hexacyanoferrate(III) ion[Fe(CN)6]3
tetrachlorocobaltate(II) ion[CoCl4]2
Name of the complexFormula
139
Metal Name in anionic complex
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Platinum
Titanate
Vanadate
Chromate
Manganate
Ferrate
Cobaltate
Nickelate
Cuprate
Zincate
Platinate
Names of some common metals in anionic complexes
140
3. (b)If the complex is cationic or neutral
the name of the metal is unchanged
followed by the oxidation number of that metal
triamminetrichlorocobalt(III)[CoCl3(NH3)3]
tetraaquadichlorochromium(III) ion[CrCl2(H2O)4]+
Name of the complexFormula
141
(a) Write the names of the following compounds.
(i) [Fe(H2O)6]Cl2
(ii) [Cu(NH3)4]Cl2
(iii) [PtCl4(NH3)2]
(iv) K2[CoCl4]
(v) [Cr(NH3)4SO4]NO3
(vi) [Co(H2O)2(NH3)3Cl]Cl
(vii) K3[AlF6]
142
Hexaaquairon(II) chloride
Tetraamminecopper(II) chloride
Diamminetetrachloroplatinum(IV)
Potassium tetrachlorocobaltate(II)
Tetraamminesulphatochromium(III) nitrate
(i) [Fe(H2O)6]Cl2
(ii) [Cu(NH3)4]Cl2
(iii) [PtCl4(NH3)2]
(iv) K2[CoCl4]
(v) [Cr(NH3)4SO4]NO3
143
(a) (vi) [Co(H2O)2(NH3)3Cl]Cl
triamminediaquachlorocobalt(II) chloride
(vii) K3[AlF6]
potassium hexafluoroaluminate Al has a fixed oxidation state (+3) no need to indicate the oxidation state
144
(b) Write the formulae of the following compounds.
(i) pentaamminechlorocobalt(III) chloride
(ii)Ammonium hexachlorotitanate(IV)
(iii) Tetraaquadihydroxoiron(II)
[Co(NH3)5Cl]Cl2
(NH4)2[TiCl6]
[Fe(H2O)4(OH)2]
145
Coordination number
of the central metal
atom or ion
Shape of complex Example
2
linear
[Ag(NH3)2]+
[Ag(CN)2]–
Stereo-structures of complexes
sp hybridized
146
[Cu(NH3)4]2+
[CuCl4]2–
Square planar
[Zn(NH3)4]2+
[CoCl4]2+
Tetrahedral4
ExampleShape of complexCoordination number
of the central metal
atom or ion
Stereo-structures of complexes
sp3
dsp2
147
Tetra-coordinated Complexes(a) Tetrahedral complexes
tetrahedral shape
blue
[Co(H2O)6]2+
Octahedral, pink
148
(b) Square planar complexes
have a square planar structure
Tetra-coordinated Complexes
149
• Example:
Tetra-coordinated Complexes
150
Coordination number
of the central metal
atom or ion
Shape of complex Example
6
Octahedral
[Cr(NH3)6]3+
[Fe(CN)6]3–
Stereo-structures of complexes
sp3d2
151
Hexa-coordinated Complexes• Example:
152
6. 6. Displacement of Ligands and Displacement of Ligands and
Relative Stability of Complex IonsRelative Stability of Complex Ions
Different ligands have different tendencies to bind with the metal atom/ion
ligands compete with one another for the metal atom/ion.
A stronger ligand can displace a weaker ligand from a complex.
153
6. 6. Displacement of Ligands and Displacement of Ligands and
Relative Stability of Complex IonsRelative Stability of Complex Ions
[Fe(H2O)6]2+(aq) + 6CN–(aq)Hexaaquairon(II) ion
[Fe(CN)6]4–(aq) + 6H2O(l)
Hexacyanoferrate(II) ion
Stronger ligand
Weaker ligand
Reversible reaction
Equilibrium position lies to the right
Kst 1024 mol6 dm18
154
[Ni(H2O)6]2+(aq) + 6NH3(aq)Hexaaquanickel(II) ion
[Ni(NH3)6]2+(aq) + 6H2O(l)Hexaamminenickel(II) ion
Stronger ligand
Weaker ligand
The greater the equilibrium constant,the stronger is the ligand on the LHS andthe more stable is the complex on the RHS
The equilibrium constant is called the stability constant, Kst
155
Consider the general equilibrium system below,
[M(H2O)x]m+ + xLn [M(L)x](m-xn)+ + xH2O
xnmx2
xn)(mx
st ]][L]O)[[M(H]][[M(L)
K
Units = (mol dm3)-x
Kst measures the stability of the complex, [M(L)x](m-
xn)+, relative to the aqua complex, [M(H2O)x]m+
156
Relative strength of some ligands bonding with copper(II) ions
monodentate
bidentate
multidentate
TAS Expt 6
157
Equilibrium Kst ((mol dm–3)–n)
[Cu(H2O)4]2+(aq) + 4Cl–(aq)
[CuCl4]2–(aq) + 4H2O(l)
[Cu(H2O)4]2+(aq) + 4NH3(aq)
[Cu(NH3)4]2+(aq) + 4H2O(l)
[Cu(H2O)4]2+(aq) + 2H2NCH2CH2NH2(aq)
[Cu(H2NCH2CH2NH2)2]2+(aq) + 4H2O(l)
[Cu(H2O)4]2+(aq) + EDTA4–(aq)
[CuEDTA]2–(aq) + 4H2O(l)
4.2 × 105
1.1 × 1013
1.0 × 1018.7
1.0 × 1018.8
What is the Kst of the formation of [Cu(H2O)4]2+(aq) ?
158
[Cu(H2O)4]2+ + 4H2O [Cu(H2O)4]2+ + 4H2O
1]]O)[[Cu(H]]O)[[Cu(H
K 242
242
st
159
Factors affecting the stability of complexes
1. The charge density of the central ion
7.7 × 104
4.5 × 1033
[Co(H2O)6]2+(aq) + 6NH3(aq)
[Co(NH3)6]2+(aq) + 6H2O(l)
[Co(H2O)6]3+(aq) + 6NH3(aq)
[Co(NH3)6]3+(aq) + 6H2O(l)
Kst (mol6 dm18)Equilibrium
≈ 1024
≈ 1031
[Fe(H2O)6]2+(aq) + 6CN–(aq)
[Fe(CN)6]4–(aq) + 6H2O(l)
[Fe(H2O)6]3+(aq) + 6CN–(aq)
[Fe(CN)6]3–(aq) + 6H2O(l)
160
Factors affecting the stability of complexes
2. The nature of ligands
Ability to form complex : -
CN > NH3 > Cl > H2O
[Zn(CN)4]2 Kst = 5 1016 mol4 dm12
[Zn(NH3)4]2+ Kst = 3.8 109 mol4 dm12
[Cu(NH3)4]2+ Kst = 1.1 1013 mol4 dm12
[CuCl4]2+ Kst = 4.2 105 mol4 dm12
161
Factors affecting the stability of complexes
3. The pH of the solution
In acidic solution, the ligands are protonated
lone pairs are not available
the complex decomposes
[Cu(NH3)4]2+(aq) + 4H2O(l) [Cu(H2O)4]2+(aq) + 4NH3(aq)
NH4+(aq)
H+
(aq)Equilibrium position shifts to the right
162
Consider the stability constants of the following silver complexes:
Ag+(aq) + 2Cl–(aq) [AgCl2]–(aq) Kst = 1.1 × 105 mol–2 dm6
Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+(aq) Kst = 1.6 × 107 mol–2 dm6
Ag+(aq) + 2CN–(aq) [Ag(CN)2]–(aq) Kst = 1.0 × 1021 mol–2 dm6
What will be formed when CN–(aq) is added to a solution of [Ag(NH3)2]+?
[Ag(CN)2](aq) and NH3
163
What will be formed when NH3(aq) is added to a solution of [Ag(CN)2]–?
No apparent reaction
Consider the stability constants of the following silver complexes:
Ag+(aq) + 2Cl–(aq) [AgCl2]–(aq) Kst = 1.1 × 105 mol–2 dm6
Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+(aq) Kst = 1.6 × 107 mol–2 dm6
Ag+(aq) + 2CN–(aq) [Ag(CN)2]–(aq) Kst = 1.0 × 1021 mol–2 dm6
164
Fe3+(aq) is too acidic.
FeSO4(aq) is used as the antidote for cyanide poisoning
[Fe(H2O)6]2+(aq) + 6CN(aq) [Fe(CN)6]4 + 6H2O(l)
Kst 1 1024 mol6 dm18 Very stable
[Fe(H2O)6]3+(aq) + H2O(l) [Fe(H2O)5OH]2+(aq) +
H3O+(aq)
Why is Fe2(SO4)3(aq) not used as the antidote ?
Only free CN is poisonous
165
[Cu(H2O)4]2+(aq) + Cl(aq) [Cu(H2O)3Cl]+(aq) + H2O(l)K1 = 6.3102 mol1 dm3
[Cu(H2O)3Cl]+(aq) + Cl(aq) [Cu(H2O)2Cl2](aq) + H2O(l)K2 = 40 mol1 dm3
[Cu(H2O)2Cl2](aq) + Cl(aq) [Cu(H2O)Cl3](aq) + H2O(l)K3 = 5.4 mol1 dm3
[Cu(H2O)Cl3](aq) + Cl(aq) [CuCl4]2(aq) + H2O(l)
K1 = 3.1 mol1 dm3
[Cu(H2O)4]2+(aq) + 4Cl(aq) [CuCl4]2(aq) + 4H2O(l)
Kst = K1 K2 K3 K4 = 4.2 105 mol4 dm12
166
K1 > K2 > K3 > K4Reasons :
1. Statistical effect
On successive displacement, less water ligands are available to be displaced.
167
K1 > K2 > K3 > K4Reasons :
[Cu(H2O)Cl3] Cl repulsion
[Cu(H2O)4]2+ Cl attraction
2. Charge effect
On successive displacement, the Cl experiences more repulsion from the complex
168
Formula of copper(II)
complex
Colour of the
complex
[Cu(H2O)4]2+
[CuCl4]2–
[Cu(NH3)4]2+
[Cu(H2NCH2CH2NH2)]2+
[Cu(EDTA)]2–
Pale blue
Yellow
Deep blue
Violet
Sky blue
Colours of some copper(II) complexes
The displacement of ligands are usually accompanied with easily observable colour changes
169
The colours of many gemstones are due to the presence of small quantities of d-block metal
ions
Coloured IonsColoured Ions
170
• Most of the d-block metals
form coloured compounds
Coloured IonsColoured Ions
due to the presence of the incompletely filled d
orbitals in thed-block metal ions
3d10 : Zn2+, Cu+; 3d0 : Sc3+, Ti4+
Which aqueous transition metal ion(s) is/are not coloured ?
171
Number of
unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous
solution
0
Sc3+
Ti4+
Zn2+
Cu+
Colourless
Colourless
Colourless
Colourless
1
Ti3+
V4+
Cu2+
Purple
Blue
Blue
Colours of some d-block metal ions in aqueous solutions
172
Number of
unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous
solution
2V3+
Ni2+
Green
Green
3
V2+
Cr3+
Co2+
Violet
Green
Pink
Colours of some d-block metal ions in aqueous solutions
173
Number of
unpaired
electrons in 3d
orbitals
d-Block metal
ion
Colour in
aqueous
solution
4
Cr2+
Mn3+
Fe2+
Blue
Violet
Green
5Mn2+
Fe3+
Very pale pink
Yellow
Colours of some d-block metal ions in aqueous solutions
174
Colours of some d-block metal ions in aqueous solutions
Co2+(aq) Fe3+(aq)Zn2+(aq)
175
Cu2+(aq)Fe2+(aq)Mn2+(aq)
Colours of some d-block metal ions in aqueous solutions
176
A substance absorbs visible light of a certain wavelength
reflects or transmits visible light of other wavelengths
(complimentary colour)
appears coloured
Coloured ionLight
absorbed
Light reflected or
transmitted
[Cu(H2O)4]2+
(aq)Yellow Blue
[CuCl4]2(aq) Blue Yellow
177
Blue
Yellow
Magenta
Green
RedCyan
Violet
Greenish yellow
Complimentary colour chart
Blue light absorbed
Appears yellow
Yellow light absorbed
Appears blue
178
• The absorption of visible light is due to the d-d electronic transition
3d 3d
i.e. an electron jumping from a lower 3d orbital to a higher 3d orbital
Coloured IonsColoured Ions
179
In gaseous state,
the five 3d orbitals are degenerate
i.e. they are of the same energy level
In the presence of ligands,
The five 3d orbitals interact with the orbitals of ligands and split into two groups of orbitals with slightly different energy levels
180
The splitting of the degenerate 3d orbitals of a d-block metal ion in an octahedral
complex
ge
gt2
222 yxzd , d
yzxzxy d,d , d
distributes along x and y axesdistributes along z
axisInteract more strongly with the orbitals of ligands
181 Higher energy eg
22 yxd
182
Criterion for d-d transition : -
presence of unpaired d electrons in the d-block metal atoms or ions
Or presence of incompletely filled d-subshelld-d transition is possible for 3d1 to 3d9 arrangements
d-d transition is NOT possible for 3d0 & 3d10 arrangements
183
3d9 : d-d transition is possible
Cu2
+
H2O as ligand
184
3d9 : d-d transition is possible
*Cu2+
Yellow light absorbed, appears blue
H2O as ligand
185
3d6 : d-d transition is possible
Fe2+
186
3d6 : d-d transition is possible
*Fe2+
Magenta light absorbed, appears green
187
3d10 : d-d transition NOT possible
Zn2+
188
3d0 : d-d transition NOT possible
Sc3+
189
E
E depends on
1. the nature and charge of metal ion
[Fe(H2O)6]2+ green,
[Fe(H2O)6]3+ yellow
[Cu(H2O)4]2+ blue,
[CuCl4]2 yellow 2. the nature of ligand
190
Why does Na+(aq) appear colourless ?
Coloured IonsColoured Ions
3d0 : d-d transition is NOT possible
2p 3s transition involves absorption of radiation in the UV region.
191
• The d-block metals and their compounds
important catalysts in industry and biological systems
Catalytic Properties of Transition Catalytic Properties of Transition Metals and their CompoundsMetals and their Compounds
192
d-Block
metalCatalyst Reaction catalyzed
VV2O5 or
vanadate(V) (VO3–)
Contact process
2SO2(g) + O2 (g) 2SO3(g)
Fe FeHaber process
N2(g) + 3H2(g) 2NH3(g)
The use of some d-block metals and their compounds as catalysts in industry
193
d-Block
metalCatalyst Reaction catalyzed
Ni Ni
Hardening of vegetable oil
(Manufacture of margarine)
RCH = CH2 + H2 RCH2CH3
Pt Pt
Catalytic oxidation of ammonia
(Manufacture of nitric(V) acid)
4NH3(g) + 5O2(g) 4NO(g) + 6H2O(l)
The use of some d-block metals and their compounds as catalysts in industry
194
• The d-block metals and their compounds exert their catalytic actions in either
heterogeneous catalysis
homogeneous catalysis
Catalytic Properties of Transition Catalytic Properties of Transition Metals and their CompoundsMetals and their Compounds
195
• Generally speaking, the function of a catalyst
provides an alternative reaction pathway of lower activation
energy
enables the reaction to proceed faster than the uncatalyzed one
Catalytic Properties of Transition Catalytic Properties of Transition Metals and their CompoundsMetals and their Compounds
196
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• The catalyst and reactants
exist in different states
• The most common heterogeneous catalysts
finely divided solids for gaseous reactions
197
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
A heterogeneous catalyst provides a suitable reaction surface for the reactants to come close together and react.
198
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• Example:
The synthesis of gaseous ammonia from nitrogen and hydrogen (i.e. Haberprocess)
N2(g) + 3H2(g) 2NH3(g)
199
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• In the absence of a catalyst
the formation of gaseous ammonia proceeds at an extremely low
rate• The probability of collision of four
gaseous molecules (i.e. one nitrogen and three hydrogen molecules)
very small
200
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• The four reactant molecules
collide in proper orientation in order to form the product
• The bond enthalpy of the reactant (N N),
very large
the reaction has a high activation energy
201
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• In the presence of iron as catalyst
the reaction proceeds much faster
provides an alternative reaction pathway of lower activation
energy
202
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• Fe is a solid
• H2, N2 and NH3 are gases
• The catalytic action occurs at the interface between these two states
• The metal provides an active reaction surface for the reaction to occur
203
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
1. Gaseous nitrogen and hydrogen molecules
diffuse to the surface of the catalyst
2. The gaseous reactant molecules
adsorbed (i.e. adhered) on the surface of the catalyst
204
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
2. The iron metal
many 3d electrons and low-lying vacant 3d orbitals
form bonds with the reactant molecules
adsorb them on its surface
weakens the bonds present in the reactant molecules
205
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
2. The free nitrogen and hydrogen atoms
come into contact with each other
readily to react and form the product3. The weak interaction between the product and the iron surface
gaseous ammonia molecules desorb easily
206
The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen
207
The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen
208
The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen
209
The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen
210
The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen
211
43.3 Characteristic Properties of the d-Block Elements and their compound (SB p.162)
1.1. Heterogeneous CatalysisHeterogeneous Catalysis
• Sometimes, the reactants
in aqueous or liquid state
• Other example:
The decomposition of hydrogen peroxide
2H2O2(aq) 2H2O(l) + O2(g)
MnO2(s) as the catalyst
212
Energy profiles of the reaction of nitrogen and hydrogen to form gaseous ammonia in the presence and absence of
a heterogeneous catalyst
213
2.2. Homogeneous CatalysisHomogeneous Catalysis
• A homogeneous catalyst
the same state as the reactants and products
the catalyst forms an intermediate with the reactants in the
reaction
changes the reaction mechanism to an another one with a lower
activation energy
214
2.2. Homogeneous CatalysisHomogeneous Catalysis
In homogeneous catalysis, the ability of the d-block metals to exhibit variableoxidation states enables the formation of the reaction intermediates.
• Example:
The reaction between peroxodisulphate(VI) ions (S2O8
2–) and iodide ions (I–)
215
2.2. Homogeneous CatalysisHomogeneous Catalysis
• Peroxodisulphate(VI) ions
oxidize iodide ions to iodine in an aqueous solution
themselves being reduced to sulphate(VI) ions
S2O82–(aq) + 2I–(aq)
2SO42–(aq) + I2
(aq) V .Eocell 511
216
2.2. Homogeneous CatalysisHomogeneous Catalysis
• Iron(III) ions
take part in the reaction by oxidizing
iodide ions to iodine
themselves being reduced to iron(II) ions2I–(aq) + 2Fe3+(aq)
I2(aq) + 2Fe2+(aq) = +0.23 V
• The reaction is very slow due to strong repulsion between like charges.
217
2.2. Homogeneous CatalysisHomogeneous Catalysis
• Iron(II) ions
subsequently oxidized by peroxodisulphate(VI) ion
the original iron(III) ions are regenerated
2Fe2+(aq) + S2O82–(aq)
2Fe3+(aq) + 2SO42–(aq) =
+1.28 V
218
2.2. Homogeneous CatalysisHomogeneous Catalysis
• The overall reaction:
2I–(aq) + 2Fe3+(aq) I2(aq) + 2Fe2+(aq) =
+0.23 V
S2O82–(aq) + 2I–(aq)
2SO42–(aq) + I2(aq) =
+1.51 V
2Fe2+(aq) + S2O82–(aq)
+) 2Fe3+(aq) + 2SO42–(aq) = +1.28 V
Feasible reaction
219
43.3 Characteristic Properties of the d-Block Elements and their compound (SB p.164)
2.2. Homogeneous CatalysisHomogeneous Catalysis
• Iron(III) ions
catalyze the reaction
acting as an intermediate for the transfer of electrons between
peroxodisulphate(VI) ions and iodide ions
220
2.2. Homogeneous CatalysisHomogeneous Catalysis
• Iodide ions
reduce Fe3+ to Fe2+
• Peroxodisulphate(VI) ions
oxidize Fe2+ to Fe3+
221
The EndThe End
222
Energy profiles for the oxidation of iodide ions by peroxodisulphate(VI) ions in the presence and absence of a homogeneous catalyst
Check Point 43-3ECheck Point 43-3E
223
Besides iron(III) ions, iron(II) ions can also catalyze the reaction between peroxodisulphate(VI) ions and
iodide ions. Why?
Answer
224
Iron(II) ions catalyze the reaction by reacting with the
peroxodisulphate(VI) ions first.
2Fe2+(aq) + S2O82–(aq) 2Fe3+(aq) + 2SO4
2–(aq)
The iron(III) ions formed then oxidize the iodide ions.
2Fe3+(aq) + 2I–(aq) 2Fe2+(aq) + I2(aq)
In this way, the reaction between peroxodisulphate(VI) ions and
iodide ions is catalyzed.
Back
225
Which of the following redox systems might catalyze the oxidation of iodide ions by peroxodisulphate(VI) ions inan aqueous solution?
Cr2O72–(aq) + 14H+(aq) + 6e–
2Cr3+(aq) + 7H2O(l) = +1.33 V
MnO4–(aq) + 8H+(aq) + 5e–
Mn2+(aq) + 4H2O(l) = +1.52 V
Sn4+(aq) + 2e– Sn2+(aq) = +0.15 V
(Given: S2O82–(aq) + 2e– 2SO4
2–(aq) = +2.01 V
I2(aq) + 2e– 2I–(aq) = +0.54 V)
Answer
226
Back
Those redox systems with greater than +0.54 V and smaller than
+2.01 V are able to catalyze the oxidation of iodide ions by
peroxodisulphate(VI) ions in an aqueous solution. Therefore, the
following two redox systems are able to catalyze the reaction.
Cr2O72–(aq) + 14H+(aq) + 6e– 2Cr3+(aq) + 7H2O(l)
MnO4–(aq) + 8H+(aq) + 5e– Mn2+(aq) + 4H2O(l)