The First Transition Series

1
d f -block
The First Transition Series
45.1 Introduction 45.2 General Features of the
d-Block Elements from Sc to Zn 45.3 Characteristi
c Properties of the d-Block Elements and their
Compounds by Sudhir Kumar PGT (Chem)
KV 1 Pathankot
2
The first transition series
3
Introduction

• 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

4

• 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 sub- shell (3d10)

5

• 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 sub-shell
• Cu2 is a transition metal ion as it has an
  incompletely filled d sub-shell

6
General Features of the d-Block Elements from Sc
to Zn
Electronic Configurations
7
General Features of the d-Block Elements from Sc
to Zn

• 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

8
General Features of the d-Block Elements from Sc
to Zn
Electronic configurations of the first series of
d-block elements
Element Atomic number Electronic configuration
Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc 21 22 23 24 25 26 27 28 29 30 Ar3d14s2 Ar3d24s2 Ar3d34s2 Ar3d54s1 Ar3d54s2 Ar3d64s2 Ar3d74s2 Ar3d84s2 Ar3d104s1 Ar3d104s2
9
General Features of the d-Block Elements from Sc
to Zn

• 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

10
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

11
General Features of the d-Block Elements from Sc
to Zn (

• 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

12
General Features of the d-Block Elements from Sc
to Zn
13
General Features of the d-Block Elements from Sc
to Zn
14
General Features of the d-Block Elements from Sc
to Zn
Atomic Radii and Ionic Radii

• Observations
• d-block metals have smaller atomic radii than
  s-block metals
• The atomic radii of the d- block 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

15
General Features of the d-Block Elements from Sc
to Zn
N
Variations in atomic and ionic radii of the first
series of d-block elements
16
General Features of the d-Block Elements from Sc
to Zn

• 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

17
General Features of the d-Block Elements from Sc
to Zn

• The atomic size increases at the end of the
  series
• ? the screening and repulsive effects of the 3d
  electrons reach a maximum
• 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

18
General Features of the d-Block Elements from Sc
to Zn
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
19
General Features of the d-Block Elements from Sc
to Zn

• 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

20
General Features of the d-Block Elements from Sc
to Zn
Ionization Enthalpy
Element Ionization enthalpy (kJ mol1) Ionization enthalpy (kJ mol1) Ionization enthalpy (kJ mol1) Ionization enthalpy (kJ mol1)
Element 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
21
General Features of the d-Block Elements from Sc
to Zn

• 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

22
General Features of the d-Block Elements from Sc
to Zn

• 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

23
General Features of the d-Block Elements from Sc
to Zn

• 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

24
General Features of the d-Block Elements from Sc
to Zn

• 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 fully-filled
  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
25
General Features of the d-Block Elements from Sc
to Zn
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.
Answer
26
General Features of the d-Block Elements from Sc
to Zn
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
27
General Features of the d-Block Elements from Sc
to Zn
Electronegativity
Electronegativity values of the s-block metals
and the first series of the d-block metals
28
General Features of the d-Block Elements from Sc
to Zn

• 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

29
General Features of the d-Block Elements from Sc
to Zn

• 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

30
General Features of the d-Block Elements from Sc
to Zn
Melting Point and Hardness
Melting points (?C) of the s-block metals and the
first series of the d-block metals
31
General Features of the d-Block Elements from Sc
to Zn

• 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 strongs-Block metals have only
  1 to 2 valence electrons per atom delocalizing
  into the electron sea

32
General Features of the d-Block Elements from Sc
to Zn

• 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

33
General Features of the d-Block Elements from Sc
to Zn
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?
Answer
34
General Features of the d-Block Elements from Sc
to Zn (
Reaction with Water
35
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

36
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
1 Cu2O Cu2Cl2
2 TiO VO CrO MnO FeO CoO NiO CuO ZnO TiCl2 VCl2 CrCl2 MnCl2 FeCl2 CoCl2 NiCl2 CuCl2 ZnCl2
3 Sc2O3 Ti2O3 V2O3 Cr2O3 Mn2O3 Fe2O3 Ni2O3xH2O ScCl3 TiCl3 VCl3 CrCl3 MnCl3 FeCl3
4 TiO2 VO2 MnO2 TiCl4 VCl4 CrCl4
5 V2O5
6 CrO3
7 Mn2O7
37
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 Possible oxidation state
Sc Ti V Cr Mn Fe Co Ni Cu Zn 3 1 2 3 4 1 2 3 4 5 1 2 3 4 5 6 1 2 3 4 5 6 7 1 2 3 4 5 6 1 2 3 4 5 1 2 3 4 5 1 2 3 2
38
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)
39
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
fully- filled configuration e.g. Ti4 is more
stable than Ti3 (? Ar3d0 configuration) Mn2
is more stable than Mn3 (? Ar3d5
configuration) Zn2 is more stable than Zn (?
Ar3d10 configuration)
40
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.177)
Variable Oxidation States of Vanadium and their
Interconversions

• 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
41
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

42
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.177)
43
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

44
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.178)
45
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.178)
46
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.179)
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
47
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 Colour
Mn2 Mn(OH)3 MnO2 MnO42 MnO4 2 3 4 6 7 Very pale pink Dark brown Black Green Purple
48
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.179)
49
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
50
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
51
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
52
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.180)
Check Point 45-3 (contd) (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 formed in both
cases. However, two different products are
produced when iron reacts with these two
chemicals respectively.
Answer
53
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

54
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
Examples of ligands
55
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

56
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.181)
57
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)42(aq), there are 4 ligands
  are bonded to the central Cu2 ion, so the
  coordination number is 4
• The most common coordination numbers are 4 and 6

58
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

59
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.182)
Diagrammatic representation of the formation of a
complex
60
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
61
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, K3Fe(CN)6 potassium
hexacyanoferrate(III) CrCl2(H2O)4Cl dichlorote
traaquachromium(III) chloride CoCl3(NH3) trich
lorotriamminecobalt(III) Note in the formulae,
the complexes are always enclosed in
62
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 Name of ligand
Bromide (Br) Chloride (Cl) Cyanide (CN) Fluoride (F) Hydroxide (OH) Sulphate(VI) (SO42) Amide (NH2) Bromo Chloro Cyano Fluoro Hydroxo Sulphato Amido Ammonia (NH3) Water (H2O) Carbon monoxide (CO) Nitric oxide (NO) Ammine Aqua Cabonyl Nitrosyl
63
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 potassium tetrachlorocobaltat
e(II) K3Fe(CN)6 potassium hexacyanoferrate(III)
CuCl42 tetrachlorocuprate(II) ion
64
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. CrCl
2(H2O)4 dichlorotetraaquachromium(III)
ion CoCl3(NH3)3 trichlorotriamminecobalt(III
)
65
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.184)
Examples 1. Ionic complexes
66
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
2. Neutral complex
67
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)6Cl2 (ii) Cu(NH3)4Cl2
(iii) PtCl4(NH3)2 (iv) K2CoCl4
Answer
68
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.185)
Check Point 45-4 (contd) (b) Write the formulae
of the following compounds. (i) chloropentaammine
cobalt(III) chloride (ii) ammonium
hexachlorotitanate(IV) (iii) dihydroxotetraaquair
on(II)
Answer
69
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

70
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

• 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

71
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)

• Example
• 0.5 M CuSO4 solution is put into a test tube. The
  complex ion present is Cu(H2O)62 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

72
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
73
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.186)
74
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 CuCl42(aq) is
  predominant over Cu(H2O)42(aq)
• ? Cl ligands can replace H2O ligands to form a
  more stable complex with Cu2 ion

75
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

76
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)
77
(No Transcript)
78
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)

• The overall stability constant for
  Cu(NH3)42(aq) is larger than that for
  CuCl42(aq)
• ? NH3 is a stronger ligand compared with Cl or
  H2O ? Cu(NH3)42(aq) is more stable than
  CuCl42(aq)

79
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.187)
80
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.188)
Equilibrium Kst ((mol dm3)n)
Co(H2O)62(aq) 6NH3(aq) Co(NH3)62(aq) 6H2O(l) Co(H2O)63(aq) 6NH3(aq) Co(NH3)63(aq) 6H2O(l) 7.7 ? 104 4.5 ? 1033
Ni(H2O)62(aq) 6NH3(aq) Ni(NH3)62(aq) 6H2O(l) 4.8 ? 107
Cu(H2O)42(aq) 4Cl CuCl42(aq) 4H2O(l) Cu(H2O)42(aq) NH3(aq) Cu(NH3)(H2O)32(aq) H2O(l) Cu(NH3)(H2O)32(aq) NH3(aq) Cu(NH3)2(H2O)22(aq) H2O(l) Cu(NH3)2(H2O)22(aq) NH3(aq) Cu(NH3)3(H2O)2(aq) H2O(l) Cu(NH3)3(H2O)2(aq) NH3(aq) Cu(NH3)42(aq) H2O(l) Cu(H2O)42(aq) 4NH3(aq) Cu(NH3)42(aq) 4H2O(l) 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)
81
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.188)

Equilibrium Kst ((mol dm3)n)
Zn(H2O)42(aq) 4CN(aq) Zn(CN)42 (aq) 4H2O(l) Zn(H2O)42(aq) 4NH3(aq) Zn(NH3)42(aq) 4H2O(l) Zn(OH)2(s) 2OH(aq) Zn(OH)42 (aq) 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

82
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 mol2
dm6 Ag(aq) 2NH3(aq) Ag(NH3)2(aq) Kst
1.6 ? 107 mol2 dm6 Ag(aq) 2CN(aq)
Ag(CN)2(aq) Kst 1.0 ? 1021 mol2
dm6 (a) Give the most stable and the least stable
complexes of silver.
Answer
83
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Check Point 45-5 (contd) Answer the following
questions by considering the stability constants
of the silver complexes. Ag(aq) 2Cl(aq)
AgCl2(aq) Kst 1.1 ? 105 mol2
dm6 Ag(aq) 2NH3(aq) Ag(NH3)2(aq) Kst
1.6 ? 107 mol2 dm6 Ag(aq) 2CN(aq)
Ag(CN)2(aq) Kst 1.0 ? 1021 mol2
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
solution of Ag(CN)2?
Answer
84
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.189)
Stereostructures of Tetra- and Hexa- Coordinated
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

85
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
86
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
87
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
88
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.191)
Shapes of tetra- and hexa-coordinated complexes
89
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.191)
Shapes of tetra- and hexa-coordinated complexes
(contd)
90
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

91
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)6Cl3
violet Cr(H2O)5ClCl2 H2O light
green Cr(H2O)4Cl2Cl 2H2O dark
green Cr(H2O)3Cl3 3H2O brown
92
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) Square planar complexes of the form
  Ma2b2 may exist in cis- or trans- form

93
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
94
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
95
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
96
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
97
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
Example
98
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.193)
(ii) Octahedral complexes of the form Ma3b3
may exist in fac- or mer- form
99
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.194)
Example
100
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Shape of complex Chemical formula Geometrical isomer Geometrical isomer
Square planar Ma2b2 cis trans
Square planar Ma2bc cis trans
101
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Shape of complex Chemical formula Geometrical isomer Geometrical isomer
Octahedral Ma4b2 cis trans
Octahedral Ma3b3 fac mer
102
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 central metal ion, a and b are two
different kinds of ligands.)
Answer
103
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.195)
Check Point 45-6 (contd) (b) Besides using
colours, suggest two experimental methods to
distinguish between the four isomers of
Cr(H2O)6Cl3 Cr(H2O)6Cl3, Cr(H2O)5ClCl2
H2O, Cr(H2O)4Cl2Cl 2H2O, Cr(H2O)3Cl3
3H2O.
Answer
104
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

105
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
• 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

106
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

107
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

108
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

109
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 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
110
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)
The colours of some hydrated d-block metal ions
(contd)
Number of unpaired d electrons Hydrated ion Colour
4 Cr2 Mn3 Fe2 Blue Violet Green
5 Mn2 Fe3 Very pale pink Yellow
111
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 colorless due to the empty
  3d sub-shell and the fully-filled 3d sub-shell
  respectively

112
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.197)

• The colors 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

113
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
114
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

115
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.198)
Heterogeneous Catalysis

• 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

116
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.199)

• 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

117
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

118
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)
119
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
120
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

121
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
• The ability of d-block metals to exhibit variable
  oxidation states enables the formation of the
  reaction intermediates

122
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)

• The standard e.m.f. calculated for the reaction
  is a highly positive value
• ? there is high tendency for the forward
  reaction to occur
• However the reaction is very slow due to kinetic
  factors

123

• Sudhir Kumar PGT (Chem)
• KV 1 Pathankot

124
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)
125
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.201)

• Fe(III) ions catalyze the reaction by acting as
  an intermediate for the transfer of electrons
  between peroxodisulphate(VI) and iodide ions

126
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
127
45.3 Characteristic Properties of the d-Block
Elements and their Compounds (SB p.202)
Answer