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Title: Back Those redox systems with greater than +0.54 V and


1
The d-Block Elements
2
Introduction
  • d-block elements
  • ? locate between the s-block and p-block
  • ? known as transition elements
  • ? occur in the fourth and subsequent periods
    of the Periodic Table

3
d-block elements
4
Introduction
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.
5
Introduction
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
Introduction
Cu 3d10 not transitional
Cu
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)
  • Physical properties vary slightly with atomic
    number across the series (cf. s-block and
    p-block elements)
  • Higher m.p./b.p./density/hardness than
    s-block elements of the same periods.
  • 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
Electronic Configurations
The building up of electronic configurations of
elements follow ? Aufbau principle ? Pauli
exclusion principle ? Hunds rule
11
Electronic Configurations
  • 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

12
Cu
Cu2
Relative energy levels of orbitals in atom and
in ion
13
Electronic Configurations
  • Valence electrons in the inner 3d orbitals
  • Examples
  • ? The electronic configuration of scandium
    1s22s22p63s23p63d14s2
  • ? The electronic configuration of zinc
    1s22s22p63s23p63d104s2

14
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
d -Block Elements as Metals
  • d-Block elements are typical metals

Physical properties of d-Block elements
? good conductors of heat and
electricity ? hard and strong ? malleable and
ductile
17
d -Block Elements as Metals
  • Physical properties of d-Block elements

? lustrous ? high melting points and boiling
points
  • Exceptions Mercury
  • ? low melting point
  • ? liquid at room temperature and pressure

18
d -Block Elements as Metals
  • d-block elements
  • ? extremely useful as construction materials
  • ? strong and unreactive

19
d -Block Elements as Metals
  • Iron

? used for construction and making machinery
nowadays
? abundant ? easy to extract
20
d -Block Elements as Metals
  • Iron

? corrodes easily ? often combined with other
elements to form steel ? harder and more
resistant to corrosion
21
d -Block Elements as Metals
  • Titanium

Corrosion resistant, light, strong and withstand
large temperature changes
? used to make aircraft and space
shuttles ? expensive
22
d -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
d -Block Elements as Metals
  • Chromium
  • ? confers inertness to stainless steel
  • Manganese
  • confers hardness wearing resistance to its
    alloys e.g. duralumin alloy of Al with Mn/Mg/Cu

24
Atomic Radii and Ionic Radii
  • Two features can be observed
  • 1. The d-block elements have smaller atomic
    radii than the s-block elements

2. The atomic radii of the d-block elements
do not show much variation across the series
25
Atomic Radii and Ionic Radii
Variation in atomic radius of the first 36
elements
26
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27
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28
On moving across the Period,
(i) Nuclear charge ? (ii) Shielding effect
(repulsion between e-) ?
29
Atomic Radii and Ionic Radii
  • At the beginning of the series
  • ? atomic number ?
  • ? effective nuclear charge ?
  • ? the electron clouds are pulled closer to
    the nucleus
  • ? atomic size ?

30
  • In the middle of the series

? more electrons enter the inner 3d
sub-shell ? The inner 3d electrons shield the
outer 4s electrons effectively
? the effective nuclear charge experienced
by 4s electrons increases very slowly ? only
a slow decrease in atomic radius in this region
31
Atomic Radii and Ionic Radii
  • At the end of the series
  • ? the screening and repulsive effects of the
    electrons in the 3d sub- shell become even
    stronger
  • ? Atomic size ?

32
Comparison of Some Physical and Chemical
Properties between the d-Block and s-Block
Elements
  • 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

33
1. Density
Densities (in g cm3) of the s-block elements and
the first series of the d-block elements at 20?C
34
1. Density
  • d-block gt 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

35
1. Density
  • 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

36
2. Ionization Enthalpy
K ? Ca (sharp ?)
Ca ? Sc (slight ?)
37
2. Ionization Enthalpy
Sc ? Cu (slight ?)
Cu ? Zn (sharp ?)
38
2. Ionization Enthalpy
  • 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

39
Sharp ? across periods 1, 2 and 3 Slight ? across
the transition series
40
2. Ionization Enthalpy
  • Going across the first transition series
  • ? the nuclear charge of the elements increases
  • ? additional electrons are added to the
    inner 3d sub-shell

41
2. Ionization Enthalpy
  • The screening effect of the additional3d
    electrons is significant
  • 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
3d10
d10/s2
43
2. Ionization Enthalpy
  • 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

44
3. Melting Points and Hardness
  • d-block gtgt s-block
  • ? 1. both 4s and 3d e- are involved in the
    formation of metal bonds
  • 2. d-block atoms are smaller

45
3. Melting Points and Hardness
K has an exceptionally small m.p. because it has
an more open b.c.c. structure.
46
Sc Ti V Cr Mn
Fe Co Ni Cu Zn 1541
1668 1910 1907 1246 1538 1495
1455 1084 419
? Unpaired electrons are relatively more involved
in the sea of electrons
47
Sc Ti V Cr Mn
Fe Co Ni Cu Zn 1541
1668 1910 1907 1246 1538 1495
1455 1084 419
3d
4s
Sc
Ti
V
  • m.p. ? from Sc to V due to the ? of unpaired
    d-electrons (from d1 to d3)

48
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
2. m.p. ? from Fe to Zn due to the ? of
unpaired d-electrons (from 4 to 0)
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
3. Melting Points and Hardness
  • The hardness of a metal depends on
  • ? the strength of the metallic bonds
  • The metallic bonds of the d-block elements are
    stronger than those of the s-block elements
  • ? much harder than the s-block elements

52
Mohs scale - A measure of hardness
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
4. Reaction with Water
  • In general, the s-block elements
  • ? react vigorously with water to form metal
    hydroxides and hydrogen
  • The d-block elements
  • ? react very slowly with cold water

? react with steam to give metal oxides and
hydrogen
54
4. Reaction with Water
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 lt Fe(OH)2 ltlt NaOH

Charge density Fe3 gt Fe2 gt Na
56
d-block compounds vs s-block compoundsA Summary
-
  • 4. less thermally stable e.g. CuCO3 ltlt 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)63(aq) H2O ?
    Fe(OH)(H2O)52(aq) H3O

57
Variable Oxidation States
  • One of the most striking properties
  • ? variable oxidation states
  • The 3d and 4s electrons are
  • ? in similar energy levels
  • ? available for bonding

58
Variable Oxidation States
  • Elements of the first transition series
  • ? form ions of roughly the same stability by
    losing different numbers of the 3d and 4s
    electrons

59
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
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
65
Draw the structure of Mn2O7
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
5. The relative stability of various oxidation
states is correlated with the stability of
electronic configurations
Stability - Mn2(aq) gt Mn3(aq)
Ar 3d5 Ar 3d4
Fe3(aq) gt Fe2(aq) Ar 3d5
Ar 3d6
69
5. The relative stability of various oxidation
states is correlated with the stability of
electronic configurations
Stability -
Zn2(aq) gt Zn(aq) Ar 3d10
Ar 3d104s1
70
1. Variable Oxidation States of Vanadium and
their Interconversions
  • 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

71
Colours of aqueous ions of vanadium of different
oxidation states
72
1. Variable Oxidation States of Vanadium and
their Interconversions
  • 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

73
1. Variable Oxidation States of Vanadium and
their Interconversions
  • In an alkaline medium
  • ? the stable form of the vanadium(V) state is

VO3(aq), metavanadate(V) or VO43(aq),
orthovanadate(V), in strongly alkaline medium
74
1. Variable Oxidation States of Vanadium and
their Interconversions
  • Compounds with vanadium in its highest oxidation
    state (i.e. 5)
  • ? strong oxidizing agents

75
1. Variable Oxidation States of Vanadium and
their Interconversions
  • Vanadium of its lowest oxidation state(i.e. 2)
  • ? in the form of V2(aq)
  • ? strong reducing agent
  • ? easily oxidized when exposed to air

76
1. Variable Oxidation States of Vanadium and
their Interconversions
  • Interconversions of the common oxidation states
    of vanadium can be carried out readily in the
    laboratory
  • The most convenient starting material
  • ? ammonium metavanadate(V) (NH4VO3)
  • ? a white solid
  • ? the oxidation state of vanadium is 5

77
1. Variable Oxidation States of Vanadium and
their Interconversions
1. Interconversions of Vanadium(V) species
Yellow orange
yellow colourless
Vanadium(V) can exist as cation as well as anion
78
1. Variable Oxidation States of Vanadium and
their Interconversions
1. Interconversions of Vanadium(V) species
Yellow orange
yellow colourless
79
1. Variable Oxidation States of Vanadium and
their Interconversions
1. Interconversions of Vanadium(V) species
Yellow orange
yellow colourless
Give the equation for the conversion V2O5 ?
VO2 V2O5(s) 2H(aq) ? 2VO2(aq) H2O(l)
80
1. Variable Oxidation States of Vanadium and
their Interconversions
1. Interconversions of Vanadium(V) species
Yellow orange
yellow colourless
Give the equation for the conversion V2O5 ?
VO3? V2O5(s) 2OH?(aq) ? 2VO3?(aq) H2O(l)
81
1. Variable Oxidation States of Vanadium and
their Interconversions
1. Interconversions of Vanadium(V) species
Yellow orange
yellow colourless
Give the equation for the conversion VO3? ?
VO2 VO3?(aq) 2H(aq) ? VO2(aq) H2O(l)
82
orthovanadate(V) ion
V5 ions does not exist in water since it
undergoes vigorous hydrolysis to give VO43?
The reaction is favoured in highly alkaline
solution
83
V ? VO43?(aq) orthovanadate(V) ion
Cr ? CrO42?(aq) chromate(VI) ion
Mn ? MnO4?(aq) manganate(VII) ion
Draw the structures of VO43?, CrO42? and MnO4?
84
Metavanadate(V) ion
The reaction is favoured in alkaline
solution VO3? is a polymeric anion like SiO32?
85
Metavanadate(V) ion, (VO3)nn?
86
The reaction is favoured in acidic solution
87
1. Variable Oxidation States of Vanadium and
their Interconversions
  • The action of zinc powder and concentrated
    hydrochloric acid
  • ? vanadium(V) ions can be reduced
    sequentially to vanadium(II) ions

88
1. Variable Oxidation States of Vanadium and
their Interconversions
V2(aq) violet
89
(a)
(b)
(c)
(d)
VO2(aq)
VO2(aq)
V3(aq)
V2(aq)
Colours of aqueous solutions of compounds
containing vanadium in four different oxidation
states(a) 5 (b) 4 (c) 3 (d) 2
90
  • The feasibility of the changes in oxidation state
    of vanadium
  • ? can be predicted using standard electrode
    potentials

91
1. Variable Oxidation States of Vanadium and
their Interconversions
  • Under standard conditions
  • ? zinc can reduce
  • 1. VO2(aq) to VO2(aq)

2. VO2(aq) to V3(aq)
3. V3(aq) to V2(aq)
92
1. Variable Oxidation States of Vanadium and
their Interconversions
93
1. Variable Oxidation States of Vanadium and
their Interconversions
94
1. Variable Oxidation States of Vanadium and
their Interconversions
95
2. Variable Oxidation States of Manganese and
their Interconversions
  • Manganese
  • ? show oxidation states of 2, 3, 4, 5, 6
    and 7 in its compounds
  • The most common oxidation states
  • ? 2, 4 and 7

96
Colours of compounds or ions of manganese in
different oxidation states
97
(a)
(b)
(c)
Mn2(aq)
Mn(OH)3(aq)
MnO2(s)
Colours of compounds or ions of manganese in
differernt oxidation states (a) 2 (b) 3 (c)
4
98
(e)
(d)
MnO42(aq)
MnO4(aq)
Colours of compounds or ions of manganese in
differernt oxidation states (d) 6 (e) 7
99
2. Variable Oxidation States of Manganese and
their Interconversions
  • Manganese of the oxidation state 2
  • ? the most stable at pH 0

100
Mn(VII)
Explosive on heating and extremely oxidizing
? in ON 2(2) 4
? in ON (?1) (?3) ?4
101
Mn(VII)
? in ON 6(2) 12
? in ON 4(?3) ?12
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)
In a neutral or alkaline medium (up to pH 14)
103
The reaction does not involve H(aq) nor OH?(aq)
104
In an acidic medium (pH 0)
In a neutral or alkaline medium (up to pH 14)
Under what conditions is the following conversion
favoured?
When OH?(aq) gt 1M
105
Mn(VI) is unstable in acidic medium
106
Mn(IV) Oxidizing in acidic medium
  • Used in the laboratory production of chlorine
  • MnO2(s) 4HCl(aq) ? MnCl2(aq) 2H2O(l)
    Cl2(g)

107
Mn(IV) Reducing in alkaline medium
108
MnO2 is oxidized to MnO42? in alkaline
medium 2MnO2 4OH? O2 ? 2MnO42?
2H2O Suggest a scheme to prepare MnO4? from MnO2
1. 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) S4O62?(aq)
standard solution
111
Formation of Complexes
  • Another striking feature of the d-block
    elements is the formation of complexes

112
Formation 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
Formation of Complexes
  • 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

114
Formation of Complexes
  • 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)6Cl3 ? Co(H2O)63 3Cl?
K3Fe(CN)6 ? 3K Fe(CN)63?
116
Criteria for complex formation
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.
2. High charge density of the central metal ions.
117
Diagrammatic representation of the formation of a
complex
118
Co(H2O)62
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. Complexes with Monodentate Ligands
A ligand that forms one dative covalent bond only
is called a monodentate ligand.
  • Examples
  • neutral ? CO, H2O, NH3
  • anionic ? Cl, CN, OH

120
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121
In the formation of complexes, classify the
transition metal ion and the ligand as a Lewis
acid or base. Explain your answer briefly.
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.
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. Complexes 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)
Oxalate (C2O42)
ethylenediamine
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. Complexes formed by Multidentate Ligands
Ligands 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
  • EDTA forms six dative covalent bonds with the
    metal ion through six atoms giving a very stable
    complex.

? hexadentate ligand
ethylenediaminetetraacetate ion
130
?
2?
FeEDTA2?
Structure of the complex ion formed by iron(II)
ions and EDTA
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.
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.
133
4. Nomenclature of Transition Metal Complexes
with Monodentate Ligands
IUPAC 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 prefixes
1 ? 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
K3Fe(CN)6 potassium hexacyanoferrate(III)
CrCl2(H2O)4Cl tetraaquadichlorochromium(III)
chloride
CoCl3(NH3)3 triamminetrichlorocobalt(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
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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
Name of the complex
Formula
tetrachlorocobaltate(II) ion
CoCl42?
hexacyanoferrate(III) ion
Fe(CN)63?
tetrachlorocuprate(II) ion
CuCl42
139
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
Name of the complex
Formula
tetraaquadichlorochromium(III) ion
CrCl2(H2O)4
triamminetrichlorocobalt(III)
CoCl3(NH3)3
141
(a) Write the names of the following
compounds. (i) Fe(H2O)6Cl2 (ii)
Cu(NH3)4Cl2 (iii) PtCl4(NH3)2 (iv)
K2CoCl4 (v) Cr(NH3)4SO4NO3 (vi)
Co(H2O)2(NH3)3ClCl (vii) K3AlF6
142
Hexaaquairon(II) chloride
Tetraamminecopper(II) chloride
Diamminetetrachloroplatinum(IV)
Potassium tetrachlorocobaltate(II)
Tetraamminesulphatochromium(III) nitrate
143
(a) (vi) Co(H2O)2(NH3)3ClCl
triamminediaquachlorocobalt(II) chloride
(vii) K3AlF6 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)5ClCl2
(NH4)2TiCl6
Fe(H2O)4(OH)2
145
Stereo-structures of complexes
sp hybridized
146
Stereo-structures of complexes
Example
Shape of complex
Coordination number of the central metal atom or
ion
Zn(NH3)42 CoCl42
Tetrahedral
4
sp3
Cu(NH3)42 CuCl42
Square planar
dsp2
147
Tetra-coordinated Complexes
  • Tetrahedral complexes
  • ? tetrahedral shape

blue
148
Tetra-coordinated Complexes
(b) Square planar complexes ? have a square
planar structure
149
Tetra-coordinated Complexes
  • Example

150
Stereo-structures of complexes
sp3d2
151
Hexa-coordinated Complexes
  • Example

152
6. Displacement of Ligands and Relative 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. Displacement of Ligands and Relative Stability
of Complex Ions
Reversible reaction Equilibrium position lies to
the right
Kst ? 1024 mol?6 dm18
154
The greater the equilibrium constant, the
stronger is the ligand on the LHS and the more
stable is the complex on the RHS The equilibrium
constant is called the stability constant, Kst
155
Consider the general equilibrium system below,
Units (mol dm?3)-x
Kst measures the stability of the complex,
M(L)x(m-xn), relative to the aqua complex,
M(H2O)xm
156
Relative strength of some ligands bonding with
copper(II) ions
TAS Expt 6
157
What is the Kst of the formation of
Cu(H2O)42(aq) ?
158
Cu(H2O)42 4H2O Cu(H2O)42
4H2O
159
Factors affecting the stability of complexes
  • The charge density of the central ion

160
Factors affecting the stability of complexes
2. The nature of ligands
Ability to form complex - CN? gt NH3 gt Cl?
gt H2O
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
162
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
164
FeSO4(aq) is used as the antidote for cyanide
poisoning
Kst ? 1 ? 1024 mol?6 dm18
Why is Fe2(SO4)3(aq) not used as the antidote ?
Fe3(aq) is too acidic.
165
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166
K1 gt K2 gt K3 gt K4
  • Reasons
  • Statistical effect
  • On successive displacement, less water ligands
    are available to be displaced.

167
K1 gt K2 gt K3 gt K4
Reasons
2. Charge effect On successive displacement, the
Cl? experiences more repulsion from the complex
168
Colours of some copper(II) complexes
The displacement of ligands are usually
accompanied with easily observable colour changes
169
Coloured Ions
The colours of many gemstones are due to the
presence of small quantities of d-block metal ions
170
Coloured Ions
  • Most of the d-block metals
  • ? form coloured compounds

? due to the presence of the incompletely
filled d orbitals in the d-block metal ions
Which aqueous transition metal ion(s) is/are not
coloured ?
3d10 Zn2, Cu 3d0 Sc3, Ti4
171
Colours of some d-block metal ions in aqueous
solutions
172
Colours of some d-block metal ions in aqueous
solutions
173
Colours of some d-block metal ions in aqueous
solutions
174
Fe3(aq)
Zn2(aq)
Co2(aq)
Colours of some d-block metal ions in aqueous
solutions
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
177
Complimentary colour chart
Blue light absorbed Appears yellow
Yellow light absorbed Appears blue
178
Coloured Ions
  • 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

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
Interact more strongly with the orbitals of
ligands
The splitting of the degenerate 3d orbitals of a
d-block metal ion in an octahedral complex
181
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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-subshell
d-d transition is possible for 3d1 to 3d9
arrangements
d-d transition is NOT possible for 3d0 3d10
arrangements
183
H2O as ligand
???
Cu2
??????
3d9 d-d transition is possible
184
H2O as ligand
Yellow light absorbed, appears blue
????
Cu2
?????
3d9 d-d transition is possible
185
Fe2
??????
3d6 d-d transition is possible
186
Magenta light absorbed, appears green
?
Fe2
?????
3d6 d-d transition is possible
187
????
Zn2
??????
3d10 d-d transition NOT possible
188
Sc3
3d0 d-d transition NOT possible
189
Fe(H2O)62 green, Fe(H2O)63 yellow
  • ?E depends on
  • the nature and charge of metal ion

Cu(H2O)42 blue, CuCl42? yellow
2. the nature of ligand
190
Coloured Ions
Why does Na(aq) appear colourless ?
3d0 d-d transition is NOT possible 2p ? 3s
transition involves absorption of radiation in
the UV region.
191
Catalytic Properties of Transition Metals and
their Compounds
  • The d-block metals and their compounds
  • ? important catalysts in industry and
    biological systems

192
The use of some d-block metals and their
compounds as catalysts in industry
193
The use of some d-block metals and their
compounds as catalysts in industry
194
Catalytic Properties of Transition Metals and
their Compounds
  • The d-block metals and their compounds exert
    their catalytic actions in either
  • ? heterogeneous catalysis
  • ? homogeneous catalysis

195
Catalytic Properties of Transition Metals and
their Compounds
  • 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

196
1. Heterogeneous Catalysis
  • The catalyst and reactants
  • ? exist in different states
  • The most common heterogeneous catalysts
  • ? finely divided solids for gaseous reactions

197
1. Heterogeneous Catalysis
A heterogeneous catalyst provides a suitable
reaction surface for the reactants to come close
together and react.
198
1. Heterogeneous Catalysis
  • Example
  • The synthesis of gaseous ammonia from nitrogen
    and hydrogen (i.e. Haberprocess)

199
1. Heterogeneous 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. Heterogeneous 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. Heterogeneous Catalysis
  • In the presence of iron as catalyst
  • ? the reaction proceeds much faster
  • ? provides an alternative reaction pathway of
    lower activation energy

202
1. Heterogeneous 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. Heterogeneous 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. Heterogeneous Catalysis
  • 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. Heterogeneous Catalysis
2. The free nitrogen and hydrogen atoms ? come
into contact with each other ? readily to react
and form the product
3. 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. Heterogeneous 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. Homogeneous 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. Homogeneous 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
    (S2O82) and iodide ions (I)

215
2. Homogeneous Catalysis
  • Peroxodisulphate(VI) ions
  • ? oxidize iodide ions to iodine in an
    aqueous solution
  • ? themselves being reduced to sulphate(VI)
    ions

216
2. Homogeneous Catalysis
  • The reaction is very slow due to strong repulsion
    between like charges.
  • Iron(III) ions
  • ? take part in the reaction by
    oxidizing iodide ions to iodine
  • ? themselves being reduced to iron(II) ions

217
2. Homogeneous Catalysis
  • Iron(II) ions
  • ? subsequently oxidized by peroxodisulphate(
    VI) ion
  • ? the original iron(III) ions are
    regenerated

218
2. Homogeneous Catalysis
  • The overall reaction

Feasible reaction
219
43.3 Characteristic Properties of the d-Block
Elements and their compound (SB p.164)
2. Homogeneous 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. Homogeneous Catalysis
  • Peroxodisulphate(VI) ions
  • ? oxidize Fe2 to Fe3
  • Iodide ions
  • ? reduce Fe3 to Fe2

221
The End
222
Energy profiles for the oxidation of iodide ions
by peroxodisulphate(VI) ions in the presence and
absence of a homogeneous catalyst
223
Let's Think 3
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)
2SO42(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
Check Point 43-3E
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
2SO42(aq) 2.01 V I2(aq)
2e 2I(aq) 0.54 V)
Answer
226
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)
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