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Chapter 45
The First Transition Series
45.1 Introduction
45.2 General Features of the d-Block Elements
from Sc to Zn
45.3 Characteristic Properties of the d-Block
Elements and their Compounds
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45.1 Introduction (SB p.164)
The first transition series
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45.1 Introduction (SB p.164)
d-Block elements (transition elements):
• Lie between s-block and p-block elements
• Occur in the fourth and subsequent periods
• All contains incomplete d sub-shell (i.e. 1 – 9 electrons) in at
least one of their oxidation state
Titanium
Scandium
Iron
3
Vanadium
Cobalt
Chromium
Manganese
Copper
Nickel
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Zinc
3
45.1 Introduction (SB p.165)
•
Strictly speaking, scandium (Sc) and zinc (Zn) are not
transitions elements
∵ Sc forms Sc3+ ion which has an empty d sub-shell (3d0)
Zn forms Zn2+ ion which has a completely filled d subshell (3d10)
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45.1 Introduction (SB p.165)
• Cu shows some intermediate behaviour between transition
and non-transition elements because of two oxidation states,
Cu(I) & Cu(II)
• Cu+ is not a transition
metal ion as it has a
completely filled d subshell
• Cu2+ is a transition metal
ion as it has an
incompletely filled
d sub-shell
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.165)
Electronic Configurations
Relative energy levels of orbitals before
and after filling with electrons
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.166)
• Before filling electrons, the energy of 4s sub-shell is
lower than that of 3d sub-shell
 4s sub-shell is filled before 3d sub-shell
• Once the 4s sub-shell is filled, the energy will increase
 The lowest energy sub-shell becomes 3d sub-shell, so
the next electron is put into 3d sub-shell
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.166)
Electronic configurations of the first series of d-block elements
Element
Scandium
Titanium
Vanadium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
8
Atomic
number
21
22
23
24
25
26
27
28
29
30
Electronic
configuration
[Ar]3d14s2
[Ar]3d24s2
[Ar]3d34s2
[Ar]3d54s1
[Ar]3d54s2
[Ar]3d64s2
[Ar]3d74s2
[Ar]3d84s2
[Ar]3d104s1
[Ar]3d104s2
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.167)
•
Cr is expected to be [Ar] 3d44s2 but the actual
configuration is [Ar] 3d54s1
•
Cu has the electronic configuration of [Ar] 3d104s1
instead of [Ar] 3d94s2
• This can be explained by the fact that a half-filled or
fully-filled d sub-shell provides extra stability
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.167)
d-Block Elements as Metals
• d-block elements are typical metals
(1) good conductors of heat and electricity, hard, strong,
malleable, ductile and lustrous
(2) high melting and boiling points except Hg is a liquid
at room temperture
• These properties make d-block elements as good
construction materials
e.g. Fe is used for construction and making machinery
Ti is used to make aircraft and space shuttles
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.168)
•
Transition elements have similar atomic radii which
make them possible for the atom of one element to
replace those of another element in the formation of
alloy
e.g. Mn is for conferring hardness and wearing resistance
to its alloy (duralumin)
Cr is for conferring inertness on stainless steel
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.168)
Iron is used to make ships
12
Tsing Ma Bridge is
constructed of steel
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.168)
Tungsten in a light bulb
The statue is made of alloy of copper and zinc
Titanium is used in making aircraft
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Jewellery made of gold
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.169)
Atomic Radii and Ionic Radii
Observations:
• d-block metals have smaller
atomic radii than s-block
metals
• The atomic radii of the dblock metals do not show
much variation across the
series
• The atomic radii decrease
initially, remain almost
constant in the middle and
then increase at the end of
series
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.170)
Variations in atomic and ionic radii of
the first series of d-block elements
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.167)
• The atomic size reduces at the beginning of the series
∵
increase in effective nuclear charge with atomic numbers
 the electron clouds are pulled closer to the nucleus
 causing a reduction in atomic size
• The atomic size decreases slowly in the middle of the series
∵
when more and more electrons enter the inner 3d sub-shell
 the screening and repulsive effects of the electrons in the
3d sub-shell increase
 the effective nuclear charge increases slowly
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.167)
•
The atomic size increases at the end of the series
∵ the screening and repulsive effects of the 3d
electrons reach a maximum
17
•
The reasons for the trend of the ionic radii of the d-block
elements are similar to those for the atomic radii.
•
Remember that the electrons have to be removed from the
4s orbital first
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.170)
Comparison of Some Physical and Chemical
Properties between d-Block and s-Block Metals
Density
Densities (in g cm-3) of the s-block metals
and the first series of d-block metals
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.171)
19
•
d-block metals are generally denser than the s-block
because most of the d-block metals have close-packed
structures while most of the s-block metals do not.
•
The densities increase generally across the first series of
d-block metals. This is in agreement with the general
decrease in atomic radius across the series
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.171)
Ionization Enthalpy
Element
20
Ionization 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
Mn
Fe
Co
Ni
Cu
Zn
632
661
648
653
716
762
757
736
745
908
1 240
1 310
1 370
1 590
1 510
1 560
1 640
1 750
1 960
1 730
2 390
2 720
2 870
2 990
3 250
2 960
3 230
3 390
3 550
3 828
7 110
4 170
4 600
4 770
5 190
5 400
5 100
5 400
5 690
5 980
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.172)
•
1st I.E. of d-block metals are greater than those of s-block
elements in the same row of the Periodic Table.
∵ the d-block metals are smaller in size than the s-block
metals, thus they have greater effective nuclear
charges
•
For K, the 2nd I.E. is exceptionally higher than its 1st I.E
•
For Ca, the 3rd I.E. is exceptionally higher than its 2nd I.E
∵ the electrons are come form the inner fully-filled electron
shells
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.172)
•
•
The first few successive I.E. for d-block elements do not
show dramatic changes
∵ removal of electrons does not involve the disruption
of inner electron shells
The 1st I.E. of the d-block metals increase slightly and
irregularly across the series
∵ Going across the first transition series, the nuclear charge
of the elements increases, and additional electrons are
found in the inner 3d sub-shell
 The additional screening effect of the additional 3d
electrons is so significant that the effective nuclear charge of
the elements increases only very slowly across the series
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.172)
23
•
Successive ionization enthalpies exhibit a similar
gradual increase across the first transition series
•
The increases in the 3rd and 4th ionization enthalpies
across the series are progressively more rapid
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.172)
• Some abnormal
high ionization
enthalpy, e.g. 1st I.E.
of Zn, 2nd I.E. of Cr
& Cu and the 3rd I.E.
of Mn
∵The removal of an
electron from a fullyfilled or half-filled
sub-shell requires a
relatively large
amount of energy
Variation of successive ionization enthalpies of
the first series of the d-block elements
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.173)
Check Point 45-1
Explain the following variation in terms of electronic
configurations.
(a) The second ionization enthalpies of both Cr and Cu are
higher
than those of their next elements respectively.
(a) The second ionization enthalpies of both Cr and Cu are higher
Answer
than those of their next elements respectively. In the case of Cr,
the
second ionization enthalpy involves the removal of an electron from a
half-filled 3d sub-shell, which has extra stability. Therefore, this second
ionization enthalpy is relatively high. The case is similar for copper where
its second ionization enthalpy involves the removal of an electron from a
fully-filled 3d sub-shell which also has extra stability. Thus, its
second ionization enthalpy is also relatively high.
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.173)
Check Point 45-1 (cont’d)
Explain the following variation in terms of electronic
configurations.
(b) The third ionization enthalpy of Mn is higher than that of
its next element.
Answer
(b) The third ionization enthalpy of Mn is higher than that
of its next element. It is because its third ionization
enthalpy involves the removal of an electron from a halffilled 3d sub-shell which has extra stability. Therefore, its
third ionization enthalpy is relatively high.
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.173)
Electronegativity
Electronegativity values of the s-block metals
and the first series of the d-block metals
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.173)
•
The electronegativity of d-block metals are generally
higher than those of the s-block metals
∵ Generally, d-block metals have smaller atomic radii
than s-block metals
 the nuclei of d-block metals can attract the electrons
in a bond more tightly towards themselves
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.173)
• The electronegativity shows a slight increase generally
with increasing atomic numbers across the series
∵
Gradual increase in effective nuclear charge and
decrease in atomic radius across the series
 The closer the electron shell to the nucleus, the more
strongly the additional electron in a bond is
attracted
 Higher electronegativity
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.174)
Melting Point and Hardness
Melting points (C) of the s-block metals and
the first series of the d-block metals
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.174)
• The melting points of the d-block metals are much higher
than those of the s-block metals
Reasons:
1. d-block metal atoms are small in size and closely packed in
the metallic lattice. All Group I metals and some Group II
metals do not have close-packed structures
2. Both 3d and 4s electrons of d-block metals participate in
metallic bonding by delocalizing into the electron sea, and
thus the metallic bond strength is very strong
s-Block metals have only 1 to 2 valence electrons per atom
delocalizing into the electron sea
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.174)
•
The hardness of a metal depends on the strength of the
metallic bonds
∵
The metallic bond of d-block metals is stronger
than that of s-block metals

d-block metals are much harder than the s-block
metals
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.174)
Check Point 45-2
What are the differences between the structures and bonding
of the d-block and s-block metals? How do these differences
affect their melting points?
The d-block metals are comparatively small, and the metallic atoms
are closely packed in the metallic lattice. Besides, both the 3d and 4s
electrons of the d-block metals participate in metallic bondingAnswer
by
delocalizing into the electron sea. The strength of metallic bond in these
metals is thus very strong. In the case of s-block metals, the metallic
radius is larger and most of them do not have close-packed structures.
Also , as they have only one or two valence electrons per atom
delocalizing into the electron sea, the metallic bond formed is
weaker. Therefore, the d-block metals have a much higher
melting point than the s-block metals.
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45.2 General Features of the d-Block Elements from Sc to Zn (SB p.175)
Reaction with Water
•
Generally, s-block metals (e.g. K, Na & Ca) react with
H2O vigorously to form metal hydroxides and H2
•
d-block metals react only very slowly with cold water.
Zn and Fe are relatively more reactive
 Zn and Fe react with steam to give metal oxides
and H2
Zn(s) + H2O(g)  ZnO(s) + H2(g)
3Fe(s) + 4H2O(g)
34
Fe3O4(s) + 4H2(g)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.175)
Variable Oxidation States
•
d-block elements has ability to show variable oxidation
states
∵ 3d & 4s electrons are of similar energy levels, the
electrons in both of them are available for bonding
 When the first transition elements react to form
compounds, they can form ions of roughly the same
stability by losing different numbers of electrons
 Form compounds with a wide variety of oxidation
states
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.175)
Oxidation states of the elements of the first
transition series in their oxides and chlorides
Oxidation
state
Oxide/Chloride
Cu2O
Cu2Cl2
+1
+2
+3
+4
+5
V2O5
+7
MnO
MnCl2
Sc2O3 Ti2O3 V2O3 Cr2O3 Mn2O3
ScCl3 TiCl3 VCl3 CrCl3 MnCl3
TiO2 VO2
TiCl4 VCl4
+6
36
TiO VO CrO
TiCl2 VCl2 CrCl2
FeO CoO NiO
FeCl2 CoCl2 NiCl2
Fe2O3
FeCl3
CuO
CuCl2
ZnO
ZnCl2
Ni2O3·xH2O
MnO2
CrCl4
CrO3
Mn2O7
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.176)
Oxidation states of the elements of the first
transition series in their compounds
Element
Sc
Ti
V
Cr
Mn
Fe
Co
Ni
Cu
Zn
37
Possible oxidation state
+1
+1
+1
+1
+1
+1
+1
+1
+2
+2
+2
+2
+2
+2
+2
+2
+2
+3
+3
+3
+3
+3
+3
+3
+3
+3
+4
+4
+4
+4
+4
+4
+4
+5
+5
+5
+5
+5
+5
+6
+6
+6
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+7
37
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.176)
Observations:
1. Sc and Zn do not exhibit variable oxidation states. Sc3+ has
electronic configuration of argon (i.e. 1s22s22p63s23p6). Zn2+
has the electronic configuration of [Ar] 3d10. Other oxidation
states are not possible.
2. Except Sc, all elements have +2 oxidation state. Except Zn,
all elements have +3 oxidation state
3. The highest oxidation state is +7 at Mn. This corresponds to
removal of all 3d & 4s electrons. (Note: max.oxidation state is
NEVER greater than the total number of 3d & 4s electrons)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.176)
4. There is a reduction in the number of oxidation states after Mn.
∵ decrease in the number of unpaired electrons and
increase in nuclear charge which holds the 3d electrons
more firmly
5. The relative stability of various oxidation states can be
correlated -with the stability of empty, half-filled and fullyfilled configuration
e.g. Ti4+ is more stable than Ti3+ (∵ [Ar]3d0 configuration)
Mn2+ is more stable than Mn3+ (∵ [Ar]3d5 configuration)
Zn2+ is more stable than Zn+ (∵ [Ar]3d10 configuration)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.177)
Variable Oxidation States of Vanadium and their
Interconversions
40
•
Vanadium shows oxidation states from +2 to +5 in its
compounds
•
In these oxidation state, vanadium forms ions which
have distinctive colours in aqueous solutions
Ion
Oxidation state
Colour
V2+
V3+
VO2+
VO2+
+2
+3
+4
+5
Violet
Green
Blue
Yellow
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.177)
•
In acidic medium, vanadium(V) state occurs as VO2+(aq);
vanadium(IV) state occurs as VO2+(aq)
•
In alkaline medium, vanadium(V) state occurs as VO3–(aq)
•
Most compounds with vanadium(V) are good oxidizing agents
while those with vanadium(II) are good reducing agents
• The starting material for the interconversions of
common oxidation states of vanadium is ammonium
vanadate(V) (NH4VO3)
• When NH4VO3 is acidified, vanadium exists in the form
of VO2+(aq) which the oxidation state of +5
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.177)
• Vanadium(V) ions can be reduced sequentially to
vanadium(II) ions by the action of Zn powder and acid
• The sequence of colour changes forms a characteristic
test for vanadium
VO2
+(aq)
yellow
42

Zn
conc. HCl
VO2+(aq)
blue

Zn
conc. HCl
V3+(aq)
Zn
 V2+(aq)
conc. HCl
green
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violet
42
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.178)
•
The feasibility of the changes in oxidation number of
vanadium can be predicted by using electrode potentials
easily
Half reaction
Zn2+(aq) + 2e–
Zn(s)
VO2+(aq) + 2H+(aq) + e–
VO2+(aq) + 2H+(aq) + e–
V3+(aq) + e–
V2+(aq)
43
E (V)
VO2+(aq) + H2O(l)
V3+(aq) + H2O(l)
New Way Chemistry for Hong Kong A-Level Book 4
–0.76
+1.00
+0.34
–0.26
43
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.178)
•
Under standard conditions, Zn can reduce vanadium(V) to
vanadium(IV) as the Ecell value is +ve
2  (VO2+(aq) + 2H+(aq) + e–
–) Zn2+(aq) + 2e–
VO2+(aq) + H2O(l)) E = +1.00 V
Zn(s)
E = –0.76 V
2VO2+(aq) + Zn(s) + 4H+(aq)
2VO2+(aq) + Zn2+(aq) + 2H2O(l)
44
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Ecell = +1.76 V
44
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.178)
•
Further reduction of vanadium(IV) to vanadium(III) by Zn is
feasible as the Ecell value is +ve
2  (VO2+(aq) + 2H+(aq) + e–
–) Zn2+(aq) + 2e–
V3+(aq) + H2O(l)) E = +0.34 V
Zn(s)
E = –0.76 V
2VO2+(aq) + Zn(s) + 4H+(aq)
2V3+(aq) + Zn2+(aq)+ 2H2O(l)
45
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Ecell = +1.10 V
45
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.179)
•
Further reduction of vanadium(III) to vanadium(II) by Zn is
also feasible
2  (V3+(aq) + e–
V2+(aq))
E = +0.34 V
–) Zn2+(aq) + 2e–
Zn(s)
E = –0.76 V
2V3+(aq) + Zn(s)
2V2+(aq) + Zn2+(aq)
Ecell = +0.50 V
Conclusion:
Zn acts as a strong reducing agent which reduces vanadium(V)
through vanadium(IV), vanadium(III) and finally to
vanadium(II) in an acidic medium
46
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.179)
Variable Oxidation States of Manganese and their
Interconversions
•
Mn shows oxidation states from +2 to +7 in its compounds
•
The most common oxidation states of Mn include +2, +4, +7
•
Mn also forms coloured compounds or ions in these
oxidation states
Ion/compound Oxidation state
Mn2+
Mn(OH)3
MnO2
MnO42–
MnO4–
47
+2
+3
+4
+6
+7
Colour
Very pale pink
Dark brown
Black
Green
Purple
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.179)
•
Mn is most stable in +2 oxidation state
•
The most common Mn compound in +4 oxidation state is
MnO2 which is a strong oxidizing agent. It reacts with
reducing agents and is reduced to Mn2+
+4
MnO2(s) + 4H+(aq) + 2e–
black
+2
Mn2+(aq) + 2H2O(l)
E = +1.23 V
very pale pink
•
MnO2 is used in the laboratory production of chlorine
MnO2(s) + 4HCl(aq)  MnCl2(aq) + 2H2O(l) + Cl2(g)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
•
The most common Mn compound in +7 oxidation state is
KMnO4 which is an extremely powerful oxidizing agent. Its
oxidizing power depends on pH
•
In acidic medium, MnO4– ions are reduced to Mn2+ ions
+7
MnO4
–(aq)
+
8H+(aq)
+
5e–
purple
+2
Mn2+(aq) + 4H2O(l)
very pale pink
E = +1.23 V
• In alkaline medium, MnO4– ions are reduced to MnO2
+7
MnO4
purple
–(aq)
+ 2H2O(l) +
3e–
+4
MnO2(s) + 4OH–(aq)
black
E = +0.59 V
49
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
Mn(II)
Mn(IV)
Mn(III)
50
Mn(VII)
Mn(VI)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
Check Point 45-3
(a) The oxidation numbers of copper in its compounds are +1
and +2.
(i) Give the names, formulae and colours of compounds
formed between copper and oxygen.
(ii) Is copper more stable in the oxidation state of +1 or +2?
Answer
(a) (i) Copper(I) oxide Cu2O – reddish brown
Copper(II) oxide CuO – black
(ii) +2
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
Check Point 45-3 (cont’d)
(b) Explain the following:
(i) When iron(II) sulphate(VI) (FeSO4) is required, it has
to be freshly prepared.
(ii) When aluminium reacts with chlorine and hydrogen
chloride respectively, aluminium chloride (AlCl3) is
(b) formed
(i) Iron(II)
solution
cannottwo
be stored
for a long
time. It
insulphate(VI)
both cases.
However,
different
products
be oxidized
by airiron
to form
iron(III)
sulphate(VI).
arewill
produced
when
reacts
with
these two
(ii) Aluminium
has only one oxidation state (+3) in its compounds,
chemicals
respectively.
whereas iron has two (+2 & +3). Iron reacts with the oxidizing
Answer
agent Cl2 to form FeCl3 but with the non-oxidizing agent
HCl to give FeCl2.
52
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52
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
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 form the dative covalent bonds
are called ligands
• In a ligand, there is at least one atom having a lone pair of
electrons which can be donated to the central metal atom or
ion to form a dative covalent bond
53
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53
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
Examples of ligands:
54
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54
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
• Depending on the overall charge of the complex formed,
complexes are classified into 3 main types: cationic, neutral
and anionic complex
Cationic complex ions
55
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55
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
Neutral complex
Anionic
complex ions
56
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56
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.182)
•
The coordination number of the central metal atom or ion
in a complex is the number of ligands bonded to this metal
atom or ion
e.g. in [Cu(NH3)4]2+(aq), there are 4 ligands are bonded to
the central Cu2+ ion, so the coordination number is 4
•
57
The most common coordination numbers are 4 and 6
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57
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.182)
•
For the first series of d-block metals, complexes are formed
using the 3d, 4s, 4p and 4d orbitals present in the metal
atoms or ions
•
Due to the presence of vacant, low energy orbitals, d-block
metals can interact with the orbitals of the surrounding
ligands
•
Due to the the relatively small sizes and high charge of
d-block metal ions, they introduce strong polarization on the
ligands. This favours the formation of bonds of high
covalent character
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58
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.182)
Diagrammatic representation of the formation of a complex
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.183)
Nomenclature of Complexes
•
Complexes are named according to the rules recommended
by IUPAC
The rules of naming a complex are as follow:
1. (a) For any ionic compound, the cation is named before the
anion.
(b) If the compound is neutral, then the name of the complex
is name of the compound
(c) In naming a complex, the ligands are named before the
central metal atom or ion, negative ones first and
then
neutral ones
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.183)
(d) The number of each type of ligands are specified by the
Greek prefixes: mono-, di-, tri-, tetra-, penta-, hexa-, etc.
(e) The oxidation number of the metal ion in the complex is
named immediately after it by Roman numerals
Therefore,
K3[Fe(CN)6]
[CrCl2(H2O)4]Cl
[CoCl3(NH3)]
potassium hexacyanoferrate(III)
dichlorotetraaquachromium(III) chloride
trichlorotriamminecobalt(III)
Note: in the formulae, the complexes are always enclosed in [ ]
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.183)
2. (a) The root names of anionic ligands always end in -o.
e.g. CN–
cyano
Cl–
chloro
(b) The names of neutral ligands are the names of the
molecules, except NH3, H2O, CO and NO
e.g. NH3
ammine
H2O
aqua
Anionic ligand
Name of
ligand
Neutral ligand
Bromide (Br–)
Bromo
Ammonia (NH3)
Chloride (Cl–)
Chloro
Water (H2O)
Cyanide (CN–)
Cyano
Carbon monoxide (CO)
Fluoride (F–)
Fluoro
Nitric oxide (NO)
Hydroxide (OH–)
Hydroxo
Sulphate(VI) (SO42–)
Sulphato
–
62Amide (NH2 )
New WayAmido
Chemistry for Hong Kong A-Level Book 4
Name of
ligand
Ammine
Aqua
Cabonyl
Nitrosyl
62
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.184)
3. (a) If the complex is anionic, then the suffix -ate is
attached to the name of the metal, followed by the
oxidation state of that metal
e.g. K2CoCl4
63
potassium tetrachlorocobaltate(II)
K3Fe(CN)6
potassium hexacyanoferrate(III)
[CuCl4]2–
tetrachlorocuprate(II) ion
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63
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.184)
Metal
Name in anionic complex
Titanium
Chromium
Manganese
Iron
Cobalt
Nickel
Copper
Zinc
Platinum
Titanate
Chromate
Manganate
Ferrate
Cobaltate
Nickelate
Cuprate
Zincate
Platinate
(b) If the complex is cationic or neutral, then the name of the
metal is unchanged.
e.g. [CrCl2(H2O)4]+
dichlorotetraaquachromium(III) ion
[CoCl3(NH3)3]
trichlorotriamminecobalt(III)
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64
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.184)
Examples:
1. Ionic complexes
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
2. Neutral complex
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
Check Point 45-4
(a) Name the following compounds.
(i) [Fe(H2O)6]Cl2
(ii) [Cu(NH3)4]Cl2
(iii) [PtCl4(NH3)2]
(iv) K2[CoCl4]
(a) (i) Hexaaquairon(II) chloride
(ii) Tetraamminecopper(II) chloride
(iii) Tetrachlorodiammineplatinum(IV)
(iv) Potassium tetrachlorocobaltate(II)
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Answer
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
Check Point 45-4 (cont’d)
(b) Write the formulae of the following compounds.
(i) chloropentaamminecobalt(III) chloride
(ii) ammonium hexachlorotitanate(IV)
(iii) dihydroxotetraaquairon(II)
Answer
(b) (i) [CoCl(NH3)5]Cl2
(ii) (NH4)2[TiCl6]
(iii) [Fe(H2O)4(OH)2]
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
Displacement of Ligands and Relative Stability
of Complex Ions
• The tendency to donate unshared electrons to form dative
covalent bonds varies with different ligands
• Different ligands form dative covalent bonds of different
strength with the metal atom or ion
• The ligand within a complex can be replaced by another
ligand if the incoming ligand can form a stronger bond with
the metal atom or ion
• When different ligands are present, they compete for a metal ion
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
• A stronger ligand (e.g. CN–, Cl–) can displace a weaker
ligand (e.g. H2O) from a complex, and a new complex is
formed
e.g. [Fe(H2O)6]2+(aq) + 6CN–(aq)
hexaaquairon(II) ion
[Ni(H2O)6]2+(aq) + 6NH3(aq)
hexaaquanickel(II) ion
•
[Fe(CN)6]4–(aq) + 6H2O(l)
hexacyanoferrate(II) ion
[Ni(NH3)6]2+(aq) + 6H2O(l)
hexaamminenickel(II) ion
Complex ions are usually coloured and the colours are
related to the types of ligands present
 Displacement of ligands usually associated with colour
changes which can be followed during experiments easily
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
Example:
71
•
0.5 M CuSO4 solution is put into a test tube. The complex
ion present is [Cu(H2O)6]2+ which is pale blue
•
Conc. HCl is added dropwise to the CuSO4 solution
•
The solution turns from pale blue to green and finally to
yellow
•
This is due to the stepwise replacement of H2O ligands
by Cl– ligands
•
Each stage is charaterized by an equilibrium constant
called the stepwise stability constant
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
[Cu(H2O)4]2+(aq) + Cl–(aq)
[Cu(H2O)3Cl]+(aq) + H2O(l)
K1 = 6.3  102 dm3 mol–1
[Cu(H2O)3Cl]+(aq) + Cl–(aq)
[Cu(H2O)2Cl2](aq) + H2O(l)
K2 = 4.0  101 dm3 mol–1
[Cu(H2O)2Cl2](aq) + Cl–(aq)
[Cu(H2O)Cl3]–(aq) + H2O(l)
K3 = 5.4 dm3 mol–1
[Cu(H2O)Cl3]–(aq) + Cl–(aq)
[CuCl4]2–(aq) + H2O(l)
K4 = 3.1 dm3 mol–1
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
Overall equation:
[Cu(H2O)4]2+(aq) + 4Cl–(aq)
[CuCl4]2–(aq) + 4H2O(l)
Overall stability constant of [CuCl4]2–(aq) is:
K st 
[[CuCl4 ]2 (aq)]eqm
[[Cu(H2O) 4 ]2 (aq)]eqm [Cl  (aq)]4 eqm
which is given by:
Kst = K1  K2  K3  K4 = 4.2  105 dm12 mol–4
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
•
The larger the overall stability constant, the more stable is
the complex
•
In this example, the overall equilibrium lies mainly on the right
and [CuCl4]2–(aq) is predominant over [Cu(H2O)4]2+(aq)
 Cl– ligands can replace H2O ligands to form a more stable
complex with Cu2+ ion
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
• The stepwise stability constant decreases from K1 to K4
Reasons:
1. When the central Cu2+ ion is surrounded by an increasing
number of Cl– ligands, the chance for an addition Cl–
ligand to replace a remaining bonded H2O decreases
2. There is a progressive change from a cationic complex to
a neutral complex, and then anionic complex. Due to the
electrostatic repulsion between anionic complex and Cl–
ions, the approach of Cl– ligands becomes more difficult
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)
•
NH3 forms a more stable complex with Cu2+ ion than Cl–
and H2O ligands do
•
NH3 can displace both H2O ligands from [Cu(H2O)4]2+(aq)
and Cl– ligands from [CuCl4]2–(aq), forming the deep blue
[Cu(NH3)4]2+(aq) ion
[Cu(H2O)4]2+(aq) + 4NH3(aq)
[Cu(NH3)4]2+(aq) + 4H2O(l)
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76
•
The displacement also occurs in stepwise reaction
[Cu(H2O)4]2+(aq) + NH3(aq)
[Cu(NH3)(H2O)3]2+(aq) + NH3(aq)
[Cu (NH3)2(H2O)2]2+(aq) + H2O(l)
K2 = 3.9  103 dm3 mol–1
[Cu(NH3)2(H2O)2]2+(aq) + NH3(aq)
[Cu (NH3)3(H2O)]2+(aq) + H2O(l)
K3 = 1.0  103 dm3 mol–1
[Cu(NH3)3(H2O)]2+(aq) + NH3(aq)
77
[Cu (NH3)(H2O)3]2+(aq) + H2O(l)
K1 = 1.9  104 dm3 mol–1
[Cu (NH3)4]2+(aq) + H2O(l)
K4 = 1.5  102 dm3 mol–1
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77
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)
•
By adding the above 4 equations, overall equation is
obtained.
[Cu(H2O)4]2+(aq) + 4NH3(aq)
[Cu(NH3)4]2+(aq) + 4H2O(l)
• Overall stability constant of [Cu(NH3)4]2+(aq) is:
K st 
[[Cu(NH3 ) 4 ]2 (aq)]eqm
[[Cu(H2O) 4 ]2 (aq)]eqm [ NH 3 (aq)]4 eqm
which is given by Kst = K1  K2  K3  K4 = 1.1  1013 dm12 mol–4
• The overall stability constant for [Cu(NH3)4]2+(aq) is
larger than that for [CuCl4]2–(aq)
 NH3 is a stronger ligand compared with Cl– or H2O
 [Cu(NH3)4]2+(aq) is more stable than [CuCl4]2–(aq)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)
• The displacement of the H2O ligands in [M(H2O)m] by
another ligand L can be represented as:
[M(H2O)m] + mL
[MLm] + mH2O
• The stability constant for the complex [MLm] at a given
temp.:
[MLm ]
K st 
[M(H 2O) m ][L]m
Equilibrium
Cr(OH)3(aq) + OH–(aq)
[Fe(H2O)6]2+(aq) + 6CN–(aq)
[Fe(H2O)6]3+(aq) + 6CN–(aq)
[Fe(H2O)4]3+(aq) + 4Cl–(aq)
79
[Cr(OH)4]–(aq)
[Fe(CN)6]4–(aq) + 6H2O(l)
[Fe(CN)6]3–(aq) + 6H2O(l)
[FeCl4]–(aq) + 4H2O(l)
New Way Chemistry for Hong Kong A-Level Book 4
Kst ((mol dm–3)–
n)
1  10–2
 1024
 1031
8  10–2
79
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.188)
Equilibrium
Kst ((mol dm–3)–n)
[Co(H2O)6]2+(aq) + 6NH3(aq)
[Co(H2O)6]3+(aq) + 6NH3(aq)
[Co(NH3)6]2+(aq) + 6H2O(l)
[Co(NH3)6]3+(aq) + 6H2O(l)
7.7  104
4.5  1033
[Ni(H2O)6]2+(aq) + 6NH3(aq)
[Ni(NH3)6]2+(aq) + 6H2O(l)
4.8  107
[Cu(H2O)4]2+(aq) + 4Cl–
[Cu(H2O)4]2+(aq) + NH3(aq)
[CuCl4]2–(aq) + 4H2O(l)
[Cu(NH3)(H2O)3]2+(aq) + H2O(l)
[Cu(NH3)(H2O)3]2+(aq) + NH3(aq)
[Cu(NH3)2(H2O)2]2+(aq) + H2O(l)
[Cu(NH3)2(H2O)2]2+(aq) + NH3(aq)
[Cu(NH3)3(H2O)]2+(aq) + H2O(l)
[Cu(NH3)3(H2O)]2+(aq) + NH3(aq)
[Cu(NH3)4]2+(aq) + H2O(l)
[Cu(H2O)4]2+(aq) + 4NH3(aq)
[Cu(NH3)4]2+(aq) + 4H2O(l)
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New Way Chemistry for Hong Kong A-Level Book 4
4.8  105
1.9  104 (K1)
3.9  103 (K2)
1.0  103 (K3)
1.5  102 (K4)
1.1  1013
(Kst = K1K2K3K4)
80
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.188)
Equilibrium
[Zn(H2O)4]2+(aq) + 4CN–(aq)
[Zn(H2O)4]2+(aq) + 4NH3(aq)
Zn(OH)2(s) + 2OH–(aq)
•
[Zn(CN)4]2– (aq) + 4H2O(l)
[Zn(NH3)4]2+(aq) + 4H2O(l)
[Zn(OH)4]2– (aq)
Kst ((mol dm–3)–n)
5  1016
3.8  109
10
As shown in the table, the values of stability constants
are very large
 The complex ions of the d-block metals are generally
very stable
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Check Point 45-5
Answer the following questions by considering the stability
constants of the 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
(a) Give the most stable and the least stable complexes of silver.
(a) The most stable complex of silver is
[Ag(CN)2]–(aq), whereas the least stable one
is [AgCl2]–(aq)
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Answer
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Check Point 45-5 (cont’d)
Answer the following questions by considering the stability
constants of the 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
(b) (i) What will be formed when CN–(aq) is added to a
solution of [Ag(NH3)2]+?
(ii) What will be formed when NH3(aq) is added to a
– and NH3(aq)
(b) (i)
[Ag(CN)2]–(aq)
solution
of [Ag(CN)
2] ?
Answer
(ii) No reaction
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Stereostructures of Tetra- and HexaCoordinated Complexes
•
The spatial arrangement of ligands around the central
metal atom or ion in a complex is referred to as the
stereochemistry of the complex
•
The coordination number of the central metal atom or ion is
determined by:
1. The size of the central metal atom or ion;
2. The number and the nature of vacant orbitals of the
d-block metal atoms or ions available for the
formation of dative covalent bonds
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Shape
1. Tetra-coordinated complexes
(a) Tetrahedral complexes
Tetrahedral shape is a common
geometry of tetra-coordinated complexes
Examples:
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85
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.190)
(b) Square planar complexes
Some tetra-coordinated complexes
show a square planar structure
Examples:
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.190)
2. Hexa-coordinated complexes
For complexes with coordination no. of 6, the
ligands occupy octahedral position to
minimize the repulsion from six electron
pairs around the central metal ion
Examples:
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.191)
Shapes of tetra- and hexa-coordinated complexes
Coordination number of the
central metal atom or ion
Shape of complex
Example
Tetrahedral
[Zn(NH3)4]2+
[CoCl4]2–
4
Square planar
[Cu(NH3)4]2+
[CuCl4]2–
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88
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.191)
Shapes of tetra- and hexa-coordinated complexes (cont’d)
Coordination number of the
central metal atom or ion
Shape of complex
Example
Octahedral
[Cr(NH3)6]3+
[Fe(CN)6]3–
6
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.191)
Isomer
Isomers are different compounds that have the same
molecular formula
• Isomers of complexes are classified into:
1. Structural isomers
2. Geometrical isomers
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.192)
1. Structural isomers
Structural isomers are isomers that have different
ligands bonded to the central metal atom or ion
Example: Cr(H2O)6Cl3 has four structural isomers
which have different colours:
[Cr(H2O)6]Cl3
[Cr(H2O)5Cl]Cl2 • H2O
[Cr(H2O)4Cl2]Cl • 2H2O
[Cr(H2O)3Cl3] • 3H2O
91
violet
light green
dark green
brown
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.192)
2. Geometrical isomers
Geometrical isomers are isomers that have different
arrangement of ligands in space
• Only square planar and octahedral complexes have
geometrical isomers
(a)
Square planar complexes
(i)
92
Square planar complexes of the form [Ma2b2]
may exist in cis- or trans- form
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.192)
Example:
Isomers in which two ligands of the same type occupy
adjacent corners of the square are called cis-isomer
Isomers in which two ligands of the same type occupy
opposite corners of the square are called trans-isomer
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
(ii) Square planar complexes of the form [Ma2bc] may
also exist in cis- or trans- form
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
(b)
Octahedral complexes
(i)
Octahedral complexes of the form [Ma4b2] may
exist in cis- or trans- form
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
Example:
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
(ii)
98
Octahedral complexes of the form [Ma3b3] may
exist in fac- or mer- form
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.194)
Example:
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Shape of Chemical
complex formula
Geometrical isomer
[Ma2b2]
Square
planar
cis
trans
cis
trans
[Ma2bc]
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Shape of
complex
Chemical
formula
Geometrical isomer
cis
trans
fac
mer
[Ma4b2]
Octahedral
[Ma3b3]
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Check Point 45-6
(a) Are there any geometrical isomers for a complex of the
form [Ma2b2]? Explain your answer with suitable
drawings.
(M represents
the planar
central
metalofion,
a and
two
(a) The square
complex
the form
[Mab2bare
2] may
exist in
cis and
forms.
different
kinds
oftrans
ligands.)
Answer
There is no geometrical isomer for a tetrahedral
complex of the form [Ma2b2]
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Check Point 45-6 (cont’d)
(b) The four isomers of chromium(III) (i.e. [Cr(H2O)6]Cl3,
(b) Besides
using
colours, suggest two experimental methods to
[Cr(H
2O)5Cl]Cl2 • H2O, [Cr(H2O)4Cl2]Cl • 2H2O and
distinguish
four
isomers
of Cr(H
[Cr(H2O)between
O) have
different
numbers
of free
Cl6–Cl
ions.
3Cl3] • 3H2the
2O)
3: One
way
to distinguish
them is by the use of acidified silver nitrate(V) solution.
[Cr(H
2O)6]Cl3, [Cr(H2O)5Cl]Cl2 • H2O,
When
excess
AgNO3(aq) is added to one mole of each
of the isomers,
3
[Cr(H
2O)4Cl2]Cl • 2H2O, [Cr(H2O)3Cl ] • 3H2O.
[Cr(H2O)6]Cl3 gives three moles of AgCl, [Cr(H2O)5Cl]Cl2 • H2O gives two
moles of AgCl, [Cr(H2O)4Cl2]Cl • 2H2O gives one mole of AgCl, and
Answer
[Cr(H2O)3Cl3] • 3H2O does not give AgCl.
Another way to distinguish them is by measuring their electrical
conductivities. As the electrical conductivity depends on the number of
ions formed when dissolved in water, [Cr(H2O)6]Cl3 has the highest
electrical conductivity whereas [Cr(H2O)3Cl3] • 3H2O has the least.
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Coloured Ions
• The natural colours of precious
gemstones are due to the existence
of small quantities of d-block
metal ions
• Most of the d-block metals form
coloured compounds and most of
their complexes are coloured too
∵ the presence of incompletely filled
d orbitals in the d-block metal ions
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.196)
•
When a substance absorbs visible light of a certain
wavelength, light of wavelengths of other regions of the
visible light spectrum will be reflected or transmitted.
 the substance will appear coloured
•
105
The absorption of light energy is associated with electronic
transition (i.e. electron jumping from a lower energy level to
a higher one). The energy required for electronic transition
is quantized
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.196)
•
If the energy involved in electronic transition does not fall
into visible light region, the substance will not appear
coloured
•
s-block and p-block elements are usually colourless
because an electronic transition is from one principle
energy level to a higher one
 the energy involved is too high in energy and it falls
into ultraviolet region
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.196)
•
For the d-block elements, the five 3d orbitals are degenerate in
gaseous ions
•
However, under the influence of a ligand, the 3d orbitals will split
into 2 groups of orbitals with slightly different energy levels
 due to the interaction of the 3d orbitals with the
electron clouds of the ligands
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.196)
•
When a sufficient amount of energy is absorbed,
electrons will be promoted from 3d orbitals at lower
energy level to those at the higher energy level
•
The energy required for the d-d transition falls within
the visible light spectrum.
 This leads to light absorption, and reflects the
remainder of the visible light
 d-block metal ions have specific colours
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)
The colours of some hydrated d-block metal ions
Number of unpaired
d electrons
109
Hydrated ion
Colour
0
Sc3+
Ti4+
Zn2+
Cu+
Colourless
1
Ti3+
V4+
Cu2+
Purple
Blue
Blue
2
V3+
Ni2+
Green
Green
3
V2+
Cr3+
Co2+
Violet
Green
Pink
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)
The colours of some hydrated d-block metal ions (cont’d)
Number of unpaired
d electrons
Co2+(aq)
110
Hydrated ion
Colour
4
Cr2+
Mn3+
Fe2+
Blue
Violet
Green
5
Mn2+
Fe3+
Very pale pink
Yellow
Zn2+(aq)
Fe3+(aq)
Mn2+(aq)
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Fe2+(aq)
Cu2+(aq)
110
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)
•
For d-d electronic transition and absorption of visible light
to occur, there must be unpaired d electrons in the d-block
metal atoms or ions
 Sc3+ and Zn2+ are colourless due to the empty 3d
sub-shell and the fully-filled 3d sub-shell
respectively
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)
•
The colours of hydrated metal ions are determined by the
oxidation states of the particular d-block elements
e.g. Fe2+(aq) is green while Fe3+(aq) is yellow
 different oxidation states are caused by different
numbers of d electrons in the d-block metal ion
 this has direct effects on the wavelength of the
radiation absorbed during electronic transition
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.198)
Catalytic Properties of Transition Metals and their Compounds
The use of some d-block metals and their compounds as
catalysts in industry
d-block element
Catalyst
Reaction catalyzed
V
Fe
Ni
Pt
113
Contact process
V2O5 or
vanadate(V)(VO3–) 2SO2(g) + O2(g)
2SO3(g)
Fe
Haber process
N2(g) + 3H2(g)
Ni
Hardening of vegetable oil
(Manufacture of margarine)
RCH = CH2 + H2  RCH2CH3
Pt
Catalytic oxidation of ammonia
(Manufacture of nitric(V) acid)
4NH3(g) + 5O2(g)  4NO(g) + 6H2O(l)
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2NH3(g)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.198)
•
d-block metals and their compounds exert their
catalytic actions in either heterogeneous catalysis or
homogeneous catalysis
•
The function of a catalyst is to provide an alternative
pathway of lower activation energy
 enabling the reaction to proceed faster than the
uncatalyzed one
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.198)
Heterogeneous Catalysis
115
•
In heterogeneous catalysis, the catalyst and reactants
are in different phases
•
The most common heterogeneous catalysts are finely
divided solids for gaseous reactions
•
A heterogenous catalyst provides a suitable
reaction surface for the reactants to come close
together and react
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.199)
e.g.:
Synthesis of gaseous ammonia from N2 and H2
N2(g) + 3H2(g)
•
2NH3(g)
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 is very small
 the four reactant molecules have to collide in a
proper orientation in order to give products
 the bond enthalpy of N  N is very large
 the reaction has a high activation energy
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.199)
•
In the presence of iron catalyst, the reaction
proceeds faster as it provides an alternative
reaction pathway
•
The catalyst exists in a different phase from that of
both reactant and products
•
The catalytic action occurs at the interface between
two phases, and the metal provides an active
reaction surface for the reaction to occur
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.200)
The catalytic
mechanism of the
formation of NH3(g)
from N2(g) and H2(g)
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.200)
Energy profiles of the reaction pathways in the
presence and absence of a heterogeneous catalyst
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.199)
Summary:
• In heterogeneous catalysis, the d-block metals or
compounds provide a suitable reaction surface for the
reaction to take place
∵
the presence of partly-filled d-orbitals
 this enables the metals to accept electrons from
reactant particles on one hand and donate electrons
to reactant particles on the other
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
Homogeneous Catalysis
•
A homogenous catalyst is in the same phase as the
reactants and products
•
The catalyst forms an intermediate with the reactants
 it changes the reaction mechanism to a new one
with a lower activation energy
•
121
The ability of d-block metals to exhibit variable
oxidation states enables the formation of the reaction
intermediates
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
• e.g. reaction between peroxodisulphate(VI) ions and
iodide ions
S2O82–(aq) + 2I–(aq)
2SO42–(aq) + I2(aq)
Ecell = +1.47 V
•
The standard e.m.f. calculated for the reaction is a highly
positive value
 there is high tendency for the forward reaction to occur
•
122
However the reaction is very slow due to kinetic factors
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
•
In catalytic process, Fe3+(aq) ions oxidizes I–(aq) to I2(aq)
with themselves being reduced to Fe2+(aq)
2I–(aq) + 2Fe3+(aq)
I2(aq) + 2Fe2+(aq)
Ecell = +0.23 V
• The Fe2+(aq) are subsequently oxidized by S2O82–(aq) and
Fe3+(aq) ions are regenerated
2Fe2+(aq) + S2O82–(aq)
123
2Fe3+(aq) + 2SO42–(aq)
Ecell = +1.24 V
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
The overall reaction:
2I–(aq) + 2Fe3+(aq)
+) 2Fe2+(aq) + S2O82–(aq)
2I–(aq) + S2O82–(aq)
•
124
I2(aq) + 2Fe2+(aq)
2Fe3+(aq) + 2SO42–(aq)
I2(aq) + 2SO42–(aq)
Fe(III) ions catalyze the reaction by acting as an
intermediate for the transfer of electrons between
peroxodisulphate(VI) and iodide ions
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
Energy profiles for the
oxidation of I–(aq) ions by
S2O82–(aq) ions in the
presence and absence of a
homogeneous catalyst
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45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.202)
Check Point 45-7
Which of the following redox systems might catalyze the
oxidation of iodide ions by peroxodisulphate(VI) ions in an
aqueous solution?
Cr2O72–(aq) + 14H+(aq) + 6e–
2Cr3+(aq) + 7H2O(l)
E = +1.33V
Systems with E greater than +0.54V and smaller than +2.01V are
+(aq) +the
able
MnO4–(aq)
+ to
8Hcatalyze
5e–oxidation of iodide
Mn2+ions
(aq)by+ peroxodisulphate(VI)
4H2O(l)
ions in an aqueous solution. Hence, the following two redox
E =systems
+1.52Vare
able to catalyze the reactions.
–
Sn4+(aq)
Sn2+
E = +0.15V
Cr2O+72–2e
(aq) + 14H+(aq)
+ (aq)
6e–
2Cr3+(aq) + 7H2O(l)
–(aq)
+(aq)
2+(aq) + 4H O(l)
2–(aq)
– + 5e– 2SO 2–
MnO
+
8H
Mn
(Given:
S24O
+
2e
(aq)
E = +2.01V
2
8
4
I2(aq) + 2e–
2I–(aq)
E = +0.54V)
Answer
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The END
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