NCERT Textbook: d & f-Block Elements | Chemistry Class 12 - NEET PDF Download

 Page 1


The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The f-block consists of elements in which 4 f and 5 f
orbitals are progressively filled. They are placed in a
separate panel at the bottom of the periodic table. The
names transition metals and inner transition metals
are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn. The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively.
Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements.
Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions. Zinc, cadmium and
mercury of group 12 have full d
10
 configuration in their
ground state as well as in their common oxidation states
and hence, are not regarded as transition metals.
However, being the end members of the 3d, 4d and 5d
transition series, respectively, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms makes transition elements different from that of
The d - and f -
Block Elements
The d- and f-
Block Elements
After studying this Unit, you will be
able to
• learn the positions of the d– and
f-block elements in the periodic
table;
• know the electronic configurations
of the transition (d-block) and the
inner transition (f-block) elements;
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values;
• describe the preparation,
properties, structures and uses
of some important compounds
such as K
2
Cr
2
O
7
 and KMnO
4
;
• understand the general
characteristics of the d– and
f–block elements and the general
horizontal and group trends in
them;
• describe the properties of the
f-block elements and give a
comparative account of the
lanthanoids and actinoids with
respect to their electronic
configurations, oxidation states
and chemical behaviour.
Objectives
Iron, copper , silver and gold are among the transition elements that
have played important roles in the development of human civilisation.
The inner transition elements such as Th, Pa and U are proving
excellent sources of nuclear energy in modern times.
4
Unit Unit Unit Unit Unit
4
Reprint 2024-25
Page 2


The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The f-block consists of elements in which 4 f and 5 f
orbitals are progressively filled. They are placed in a
separate panel at the bottom of the periodic table. The
names transition metals and inner transition metals
are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn. The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively.
Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements.
Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions. Zinc, cadmium and
mercury of group 12 have full d
10
 configuration in their
ground state as well as in their common oxidation states
and hence, are not regarded as transition metals.
However, being the end members of the 3d, 4d and 5d
transition series, respectively, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms makes transition elements different from that of
The d - and f -
Block Elements
The d- and f-
Block Elements
After studying this Unit, you will be
able to
• learn the positions of the d– and
f-block elements in the periodic
table;
• know the electronic configurations
of the transition (d-block) and the
inner transition (f-block) elements;
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values;
• describe the preparation,
properties, structures and uses
of some important compounds
such as K
2
Cr
2
O
7
 and KMnO
4
;
• understand the general
characteristics of the d– and
f–block elements and the general
horizontal and group trends in
them;
• describe the properties of the
f-block elements and give a
comparative account of the
lanthanoids and actinoids with
respect to their electronic
configurations, oxidation states
and chemical behaviour.
Objectives
Iron, copper , silver and gold are among the transition elements that
have played important roles in the development of human civilisation.
The inner transition elements such as Th, Pa and U are proving
excellent sources of nuclear energy in modern times.
4
Unit Unit Unit Unit Unit
4
Reprint 2024-25
90 Chemistry
the non-transition elements. Hence, transition elements
and their compounds are studied separately. However,
the usual theory of valence as applicable to the non-
transition elements can be applied successfully to the
transition elements also.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium belong to the transition metals series.
In this Unit, we shall first deal with the electronic
configuration, occurrence and general characteristics of
transition elements with special emphasis on the trends
in the properties of the first row (3d) transition metals
along with the preparation and properties of some
important compounds. This will be followed by
consideration of certain general aspects such as electronic
configurations, oxidation states and chemical reactivity
of the inner transition metals.
THE TRANSITION ELEMENTS (d-BLOCK)
The d–block occupies the large middle section of the periodic table
flanked between s– and p– blocks in the periodic table. The d–orbitals
of the penultimate energy level of atoms receive electrons giving rise to
four rows of the transition metals, i.e., 3d, 4d, 5d and 6d. All these
series of transition elements are shown in Table 4.1.
In general the electronic configuration of outer orbitals of these elements
is (n-1)d
1– 10
ns
1–2
except for Pd where its electronic configuration is 4d
10
5s
0
.
The (n–1) stands for the inner d orbitals which may have one to ten
electrons and the outermost ns orbital may have one or two electrons.
However, this generalisation has several exceptions because of very
little energy difference between (n-1)d and ns orbitals. Furthermore,
half and completely filled sets of orbitals are relatively more stable. A
consequence of this factor is reflected in the electronic configurations
of Cr and Cu in the 3d series. For example, consider the case of Cr,
which has 3d
5 
4s
1
 configuration instead of 3d
4
4s
2
; the energy gap
between the two sets (3d and 4s) of orbitals is small enough to prevent
electron entering the 3d orbitals. Similarly in case of Cu, the
configuration is 3d
10
4s
1
 and not 3d
9
4s
2
. The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 4.1.
4.1 4.1 4.1 4.1 4.1 Position in the Position in the Position in the Position in the Position in the
Periodic Table Periodic Table Periodic Table Periodic Table Periodic Table
4.2 4.2 4.2 4.2 4.2 Electronic Electronic Electronic Electronic Electronic
Configurations Configurations Configurations Configurations Configurations
of the d-Block of the d-Block of the d-Block of the d-Block of the d-Block
Elements Elements Elements Elements Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Z 21 22 23 24 25 26 27 28 29 30
4s 2 2 2 1 2 2 2 2 1 2
3d 1 2 3 5 5 6 7 8 10 10
1st Series
Table 4.1: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
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Page 3


The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The f-block consists of elements in which 4 f and 5 f
orbitals are progressively filled. They are placed in a
separate panel at the bottom of the periodic table. The
names transition metals and inner transition metals
are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn. The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively.
Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements.
Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions. Zinc, cadmium and
mercury of group 12 have full d
10
 configuration in their
ground state as well as in their common oxidation states
and hence, are not regarded as transition metals.
However, being the end members of the 3d, 4d and 5d
transition series, respectively, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms makes transition elements different from that of
The d - and f -
Block Elements
The d- and f-
Block Elements
After studying this Unit, you will be
able to
• learn the positions of the d– and
f-block elements in the periodic
table;
• know the electronic configurations
of the transition (d-block) and the
inner transition (f-block) elements;
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values;
• describe the preparation,
properties, structures and uses
of some important compounds
such as K
2
Cr
2
O
7
 and KMnO
4
;
• understand the general
characteristics of the d– and
f–block elements and the general
horizontal and group trends in
them;
• describe the properties of the
f-block elements and give a
comparative account of the
lanthanoids and actinoids with
respect to their electronic
configurations, oxidation states
and chemical behaviour.
Objectives
Iron, copper , silver and gold are among the transition elements that
have played important roles in the development of human civilisation.
The inner transition elements such as Th, Pa and U are proving
excellent sources of nuclear energy in modern times.
4
Unit Unit Unit Unit Unit
4
Reprint 2024-25
90 Chemistry
the non-transition elements. Hence, transition elements
and their compounds are studied separately. However,
the usual theory of valence as applicable to the non-
transition elements can be applied successfully to the
transition elements also.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium belong to the transition metals series.
In this Unit, we shall first deal with the electronic
configuration, occurrence and general characteristics of
transition elements with special emphasis on the trends
in the properties of the first row (3d) transition metals
along with the preparation and properties of some
important compounds. This will be followed by
consideration of certain general aspects such as electronic
configurations, oxidation states and chemical reactivity
of the inner transition metals.
THE TRANSITION ELEMENTS (d-BLOCK)
The d–block occupies the large middle section of the periodic table
flanked between s– and p– blocks in the periodic table. The d–orbitals
of the penultimate energy level of atoms receive electrons giving rise to
four rows of the transition metals, i.e., 3d, 4d, 5d and 6d. All these
series of transition elements are shown in Table 4.1.
In general the electronic configuration of outer orbitals of these elements
is (n-1)d
1– 10
ns
1–2
except for Pd where its electronic configuration is 4d
10
5s
0
.
The (n–1) stands for the inner d orbitals which may have one to ten
electrons and the outermost ns orbital may have one or two electrons.
However, this generalisation has several exceptions because of very
little energy difference between (n-1)d and ns orbitals. Furthermore,
half and completely filled sets of orbitals are relatively more stable. A
consequence of this factor is reflected in the electronic configurations
of Cr and Cu in the 3d series. For example, consider the case of Cr,
which has 3d
5 
4s
1
 configuration instead of 3d
4
4s
2
; the energy gap
between the two sets (3d and 4s) of orbitals is small enough to prevent
electron entering the 3d orbitals. Similarly in case of Cu, the
configuration is 3d
10
4s
1
 and not 3d
9
4s
2
. The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 4.1.
4.1 4.1 4.1 4.1 4.1 Position in the Position in the Position in the Position in the Position in the
Periodic Table Periodic Table Periodic Table Periodic Table Periodic Table
4.2 4.2 4.2 4.2 4.2 Electronic Electronic Electronic Electronic Electronic
Configurations Configurations Configurations Configurations Configurations
of the d-Block of the d-Block of the d-Block of the d-Block of the d-Block
Elements Elements Elements Elements Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Z 21 22 23 24 25 26 27 28 29 30
4s 2 2 2 1 2 2 2 2 1 2
3d 1 2 3 5 5 6 7 8 10 10
1st Series
Table 4.1: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
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91 The d- and f- Block Elements
The electronic configurations of outer orbitals of Zn, Cd, Hg and Cn
are represented by the general formula (n-1)d
10
ns
2
. The orbitals in
these elements are completely filled in the ground state as well as in
their common oxidation states. Therefore, they are not regarded as
transition elements.
The d orbitals of the transition elements protrude to the periphery of
an atom more than the other orbitals (i.e., s and p), hence, they are more
influenced by the surroundings as well as affect the atoms or molecules
surrounding them. In some respects, ions of a given d
n
 configuration
(n = 1 – 9) have similar magnetic and electronic properties. With partly
filled d orbitals these elements exhibit certain characteristic properties
such as display of a variety of oxidation states, formation of coloured
ions and entering into complex formation with a variety of ligands.
The transition metals and their compounds also exhibit catalytic
property and paramagnetic behaviour. All these characteristics have
been discussed in detail later in this Unit.
There are greater similarities in the properties of the transition
elements of a horizontal row in contrast to the non-transition elements.
However, some group similarities also exist. We shall first study the
general characteristics and their trends in the horizontal rows
(particularly 3d row) and then consider some group similarities.
2nd Series
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
Z 39 40 41 42 43 44 45 46 47 48
5s 2 2 1 1 1 1 1 0 1 2
4d 1 2 4 5 6 7 8 10 10 10
3rd Series
La Hf Ta W Re Os Ir Pt Au Hg
Z 57 72 73 74 75 76 77 78 79 80
6s 2 2 2 2 2 2 2 1 1 2
5d 1 2 3 4 5 6 7 9 10 10
Ac Rf Db Sg Bh Hs Mt Ds Rg Cn
Z 89 104 105 106 107 108 109 110 111 112
7s 2 2 2 2 2 2 2 2 1 2
6d 1 2 3 4 5 6 7 8 10 10
4th Series
On what ground can you say that scandium (Z = 21) is a transition
element but zinc (Z = 30) is not?
On the basis of incompletely filled 3d orbitals in case of scandium atom
in its ground state (3d
1
), it is regarded as a transition element. On the
other hand, zinc atom has completely filled d orbitals (3d
10
) in its
ground state as well as in its oxidised state, hence it is not regarded
as a transition element.
Example 4.1 Example 4.1 Example 4.1 Example 4.1 Example 4.1
Solution Solution Solution Solution Solution
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Page 4


The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The f-block consists of elements in which 4 f and 5 f
orbitals are progressively filled. They are placed in a
separate panel at the bottom of the periodic table. The
names transition metals and inner transition metals
are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn. The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively.
Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements.
Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions. Zinc, cadmium and
mercury of group 12 have full d
10
 configuration in their
ground state as well as in their common oxidation states
and hence, are not regarded as transition metals.
However, being the end members of the 3d, 4d and 5d
transition series, respectively, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms makes transition elements different from that of
The d - and f -
Block Elements
The d- and f-
Block Elements
After studying this Unit, you will be
able to
• learn the positions of the d– and
f-block elements in the periodic
table;
• know the electronic configurations
of the transition (d-block) and the
inner transition (f-block) elements;
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values;
• describe the preparation,
properties, structures and uses
of some important compounds
such as K
2
Cr
2
O
7
 and KMnO
4
;
• understand the general
characteristics of the d– and
f–block elements and the general
horizontal and group trends in
them;
• describe the properties of the
f-block elements and give a
comparative account of the
lanthanoids and actinoids with
respect to their electronic
configurations, oxidation states
and chemical behaviour.
Objectives
Iron, copper , silver and gold are among the transition elements that
have played important roles in the development of human civilisation.
The inner transition elements such as Th, Pa and U are proving
excellent sources of nuclear energy in modern times.
4
Unit Unit Unit Unit Unit
4
Reprint 2024-25
90 Chemistry
the non-transition elements. Hence, transition elements
and their compounds are studied separately. However,
the usual theory of valence as applicable to the non-
transition elements can be applied successfully to the
transition elements also.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium belong to the transition metals series.
In this Unit, we shall first deal with the electronic
configuration, occurrence and general characteristics of
transition elements with special emphasis on the trends
in the properties of the first row (3d) transition metals
along with the preparation and properties of some
important compounds. This will be followed by
consideration of certain general aspects such as electronic
configurations, oxidation states and chemical reactivity
of the inner transition metals.
THE TRANSITION ELEMENTS (d-BLOCK)
The d–block occupies the large middle section of the periodic table
flanked between s– and p– blocks in the periodic table. The d–orbitals
of the penultimate energy level of atoms receive electrons giving rise to
four rows of the transition metals, i.e., 3d, 4d, 5d and 6d. All these
series of transition elements are shown in Table 4.1.
In general the electronic configuration of outer orbitals of these elements
is (n-1)d
1– 10
ns
1–2
except for Pd where its electronic configuration is 4d
10
5s
0
.
The (n–1) stands for the inner d orbitals which may have one to ten
electrons and the outermost ns orbital may have one or two electrons.
However, this generalisation has several exceptions because of very
little energy difference between (n-1)d and ns orbitals. Furthermore,
half and completely filled sets of orbitals are relatively more stable. A
consequence of this factor is reflected in the electronic configurations
of Cr and Cu in the 3d series. For example, consider the case of Cr,
which has 3d
5 
4s
1
 configuration instead of 3d
4
4s
2
; the energy gap
between the two sets (3d and 4s) of orbitals is small enough to prevent
electron entering the 3d orbitals. Similarly in case of Cu, the
configuration is 3d
10
4s
1
 and not 3d
9
4s
2
. The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 4.1.
4.1 4.1 4.1 4.1 4.1 Position in the Position in the Position in the Position in the Position in the
Periodic Table Periodic Table Periodic Table Periodic Table Periodic Table
4.2 4.2 4.2 4.2 4.2 Electronic Electronic Electronic Electronic Electronic
Configurations Configurations Configurations Configurations Configurations
of the d-Block of the d-Block of the d-Block of the d-Block of the d-Block
Elements Elements Elements Elements Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Z 21 22 23 24 25 26 27 28 29 30
4s 2 2 2 1 2 2 2 2 1 2
3d 1 2 3 5 5 6 7 8 10 10
1st Series
Table 4.1: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
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91 The d- and f- Block Elements
The electronic configurations of outer orbitals of Zn, Cd, Hg and Cn
are represented by the general formula (n-1)d
10
ns
2
. The orbitals in
these elements are completely filled in the ground state as well as in
their common oxidation states. Therefore, they are not regarded as
transition elements.
The d orbitals of the transition elements protrude to the periphery of
an atom more than the other orbitals (i.e., s and p), hence, they are more
influenced by the surroundings as well as affect the atoms or molecules
surrounding them. In some respects, ions of a given d
n
 configuration
(n = 1 – 9) have similar magnetic and electronic properties. With partly
filled d orbitals these elements exhibit certain characteristic properties
such as display of a variety of oxidation states, formation of coloured
ions and entering into complex formation with a variety of ligands.
The transition metals and their compounds also exhibit catalytic
property and paramagnetic behaviour. All these characteristics have
been discussed in detail later in this Unit.
There are greater similarities in the properties of the transition
elements of a horizontal row in contrast to the non-transition elements.
However, some group similarities also exist. We shall first study the
general characteristics and their trends in the horizontal rows
(particularly 3d row) and then consider some group similarities.
2nd Series
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
Z 39 40 41 42 43 44 45 46 47 48
5s 2 2 1 1 1 1 1 0 1 2
4d 1 2 4 5 6 7 8 10 10 10
3rd Series
La Hf Ta W Re Os Ir Pt Au Hg
Z 57 72 73 74 75 76 77 78 79 80
6s 2 2 2 2 2 2 2 1 1 2
5d 1 2 3 4 5 6 7 9 10 10
Ac Rf Db Sg Bh Hs Mt Ds Rg Cn
Z 89 104 105 106 107 108 109 110 111 112
7s 2 2 2 2 2 2 2 2 1 2
6d 1 2 3 4 5 6 7 8 10 10
4th Series
On what ground can you say that scandium (Z = 21) is a transition
element but zinc (Z = 30) is not?
On the basis of incompletely filled 3d orbitals in case of scandium atom
in its ground state (3d
1
), it is regarded as a transition element. On the
other hand, zinc atom has completely filled d orbitals (3d
10
) in its
ground state as well as in its oxidised state, hence it is not regarded
as a transition element.
Example 4.1 Example 4.1 Example 4.1 Example 4.1 Example 4.1
Solution Solution Solution Solution Solution
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92 Chemistry
1
2
3
4
M.p./10 K
3
Ti
Zr
Hf
W
Re
Ta
Os
Ir
Ru
Mo
Nb
Tc
Rh
Cr
V
Mn
Fe
Co
Ni
Pd
Pt
Cu
Au
Ag
Atomic number
Intext Question Intext Question Intext Question Intext Question Intext Question
4.1 Silver atom has completely filled d orbitals (4d
10
) in its ground state.
How can you say that it is a transition element?
We will discuss the properties of elements of first transition series
only in the following sections.
4.3.1 Physical Properties
Nearly all the transition elements display typical metallic properties
such as high tensile strength, ductility, malleability, high thermal and
electrical conductivity and metallic lustre.  With the exceptions of Zn,
Cd, Hg and Mn, they have one or more typical metallic structures at
normal temperatures.
4.3 4.3 4.3 4.3 4.3 General General General General General
Properties of Properties of Properties of Properties of Properties of
the Transition the Transition the Transition the Transition the Transition
Elements Elements Elements Elements Elements
(d-Block) (d-Block) (d-Block) (d-Block) (d-Block)
(bcc = body centred cubic; hcp = hexagonal close packed;
ccp = cubic close packed; X = a typical metal structure).
Fig. 4.1: Trends in melting points of
transition elements
The transition metals (with the exception
of Zn, Cd and Hg) are very hard and have low
volatility. Their melting and boiling points are
high. Fig. 4.1 depicts the melting points of
transition metals belonging to 3d, 4d and 5d
series. The high melting points of these metals
are attributed to the involvement of greater
number of electrons from (n-1)d in addition to
the ns electrons in the interatomic metallic
bonding. In any row the melting points of these
metals rise to a maximum at d
5
 except for
anomalous values of Mn and Tc and fall
regularly as the atomic number increases.
They have high enthalpies of atomisation which
are shown in Fig. 4.2.  The maxima at about
the middle of each series indicate that one
unpaired electron per d orbital is particularly
Lattice Structures of Transition Metals
Sc Ti V Cr Mn Fe Co Ni Cu Zn
hcp hcp bcc bcc X bcc ccp ccp ccp X
(bcc) (bcc) (bcc, ccp) (hcp) (hcp) (hcp)
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
hcp hcp bcc bcc hcp hcp ccp ccp ccp X
(bcc) (bcc) (hcp)
La Hf Ta W Re Os Ir Pt Au Hg
hcp hcp bcc bcc hcp hcp ccp ccp ccp X
(ccp,bcc) (bcc)
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Page 5


The d-block of the periodic table contains the elements
of the groups 3-12 in which the d orbitals are
progressively filled in each of the four long periods.
The f-block consists of elements in which 4 f and 5 f
orbitals are progressively filled. They are placed in a
separate panel at the bottom of the periodic table. The
names transition metals and inner transition metals
are often used to refer to the elements of d-and
f-blocks respectively.
There are mainly four series of the transition metals,
3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
and Hf to Hg) and 6d series which has Ac and elements
from Rf to Cn. The two series of the inner transition
metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
lanthanoids and actinoids respectively.
Originally the name transition metals was derived
from the fact that their chemical properties were
transitional between those of s and p-block elements.
Now according to IUPAC, transition metals are defined
as metals which have incomplete d subshell either in
neutral atom or in their ions. Zinc, cadmium and
mercury of group 12 have full d
10
 configuration in their
ground state as well as in their common oxidation states
and hence, are not regarded as transition metals.
However, being the end members of the 3d, 4d and 5d
transition series, respectively, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms makes transition elements different from that of
The d - and f -
Block Elements
The d- and f-
Block Elements
After studying this Unit, you will be
able to
• learn the positions of the d– and
f-block elements in the periodic
table;
• know the electronic configurations
of the transition (d-block) and the
inner transition (f-block) elements;
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values;
• describe the preparation,
properties, structures and uses
of some important compounds
such as K
2
Cr
2
O
7
 and KMnO
4
;
• understand the general
characteristics of the d– and
f–block elements and the general
horizontal and group trends in
them;
• describe the properties of the
f-block elements and give a
comparative account of the
lanthanoids and actinoids with
respect to their electronic
configurations, oxidation states
and chemical behaviour.
Objectives
Iron, copper , silver and gold are among the transition elements that
have played important roles in the development of human civilisation.
The inner transition elements such as Th, Pa and U are proving
excellent sources of nuclear energy in modern times.
4
Unit Unit Unit Unit Unit
4
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90 Chemistry
the non-transition elements. Hence, transition elements
and their compounds are studied separately. However,
the usual theory of valence as applicable to the non-
transition elements can be applied successfully to the
transition elements also.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium belong to the transition metals series.
In this Unit, we shall first deal with the electronic
configuration, occurrence and general characteristics of
transition elements with special emphasis on the trends
in the properties of the first row (3d) transition metals
along with the preparation and properties of some
important compounds. This will be followed by
consideration of certain general aspects such as electronic
configurations, oxidation states and chemical reactivity
of the inner transition metals.
THE TRANSITION ELEMENTS (d-BLOCK)
The d–block occupies the large middle section of the periodic table
flanked between s– and p– blocks in the periodic table. The d–orbitals
of the penultimate energy level of atoms receive electrons giving rise to
four rows of the transition metals, i.e., 3d, 4d, 5d and 6d. All these
series of transition elements are shown in Table 4.1.
In general the electronic configuration of outer orbitals of these elements
is (n-1)d
1– 10
ns
1–2
except for Pd where its electronic configuration is 4d
10
5s
0
.
The (n–1) stands for the inner d orbitals which may have one to ten
electrons and the outermost ns orbital may have one or two electrons.
However, this generalisation has several exceptions because of very
little energy difference between (n-1)d and ns orbitals. Furthermore,
half and completely filled sets of orbitals are relatively more stable. A
consequence of this factor is reflected in the electronic configurations
of Cr and Cu in the 3d series. For example, consider the case of Cr,
which has 3d
5 
4s
1
 configuration instead of 3d
4
4s
2
; the energy gap
between the two sets (3d and 4s) of orbitals is small enough to prevent
electron entering the 3d orbitals. Similarly in case of Cu, the
configuration is 3d
10
4s
1
 and not 3d
9
4s
2
. The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 4.1.
4.1 4.1 4.1 4.1 4.1 Position in the Position in the Position in the Position in the Position in the
Periodic Table Periodic Table Periodic Table Periodic Table Periodic Table
4.2 4.2 4.2 4.2 4.2 Electronic Electronic Electronic Electronic Electronic
Configurations Configurations Configurations Configurations Configurations
of the d-Block of the d-Block of the d-Block of the d-Block of the d-Block
Elements Elements Elements Elements Elements
Sc Ti V Cr Mn Fe Co Ni Cu Zn
Z 21 22 23 24 25 26 27 28 29 30
4s 2 2 2 1 2 2 2 2 1 2
3d 1 2 3 5 5 6 7 8 10 10
1st Series
Table 4.1: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
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91 The d- and f- Block Elements
The electronic configurations of outer orbitals of Zn, Cd, Hg and Cn
are represented by the general formula (n-1)d
10
ns
2
. The orbitals in
these elements are completely filled in the ground state as well as in
their common oxidation states. Therefore, they are not regarded as
transition elements.
The d orbitals of the transition elements protrude to the periphery of
an atom more than the other orbitals (i.e., s and p), hence, they are more
influenced by the surroundings as well as affect the atoms or molecules
surrounding them. In some respects, ions of a given d
n
 configuration
(n = 1 – 9) have similar magnetic and electronic properties. With partly
filled d orbitals these elements exhibit certain characteristic properties
such as display of a variety of oxidation states, formation of coloured
ions and entering into complex formation with a variety of ligands.
The transition metals and their compounds also exhibit catalytic
property and paramagnetic behaviour. All these characteristics have
been discussed in detail later in this Unit.
There are greater similarities in the properties of the transition
elements of a horizontal row in contrast to the non-transition elements.
However, some group similarities also exist. We shall first study the
general characteristics and their trends in the horizontal rows
(particularly 3d row) and then consider some group similarities.
2nd Series
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
Z 39 40 41 42 43 44 45 46 47 48
5s 2 2 1 1 1 1 1 0 1 2
4d 1 2 4 5 6 7 8 10 10 10
3rd Series
La Hf Ta W Re Os Ir Pt Au Hg
Z 57 72 73 74 75 76 77 78 79 80
6s 2 2 2 2 2 2 2 1 1 2
5d 1 2 3 4 5 6 7 9 10 10
Ac Rf Db Sg Bh Hs Mt Ds Rg Cn
Z 89 104 105 106 107 108 109 110 111 112
7s 2 2 2 2 2 2 2 2 1 2
6d 1 2 3 4 5 6 7 8 10 10
4th Series
On what ground can you say that scandium (Z = 21) is a transition
element but zinc (Z = 30) is not?
On the basis of incompletely filled 3d orbitals in case of scandium atom
in its ground state (3d
1
), it is regarded as a transition element. On the
other hand, zinc atom has completely filled d orbitals (3d
10
) in its
ground state as well as in its oxidised state, hence it is not regarded
as a transition element.
Example 4.1 Example 4.1 Example 4.1 Example 4.1 Example 4.1
Solution Solution Solution Solution Solution
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92 Chemistry
1
2
3
4
M.p./10 K
3
Ti
Zr
Hf
W
Re
Ta
Os
Ir
Ru
Mo
Nb
Tc
Rh
Cr
V
Mn
Fe
Co
Ni
Pd
Pt
Cu
Au
Ag
Atomic number
Intext Question Intext Question Intext Question Intext Question Intext Question
4.1 Silver atom has completely filled d orbitals (4d
10
) in its ground state.
How can you say that it is a transition element?
We will discuss the properties of elements of first transition series
only in the following sections.
4.3.1 Physical Properties
Nearly all the transition elements display typical metallic properties
such as high tensile strength, ductility, malleability, high thermal and
electrical conductivity and metallic lustre.  With the exceptions of Zn,
Cd, Hg and Mn, they have one or more typical metallic structures at
normal temperatures.
4.3 4.3 4.3 4.3 4.3 General General General General General
Properties of Properties of Properties of Properties of Properties of
the Transition the Transition the Transition the Transition the Transition
Elements Elements Elements Elements Elements
(d-Block) (d-Block) (d-Block) (d-Block) (d-Block)
(bcc = body centred cubic; hcp = hexagonal close packed;
ccp = cubic close packed; X = a typical metal structure).
Fig. 4.1: Trends in melting points of
transition elements
The transition metals (with the exception
of Zn, Cd and Hg) are very hard and have low
volatility. Their melting and boiling points are
high. Fig. 4.1 depicts the melting points of
transition metals belonging to 3d, 4d and 5d
series. The high melting points of these metals
are attributed to the involvement of greater
number of electrons from (n-1)d in addition to
the ns electrons in the interatomic metallic
bonding. In any row the melting points of these
metals rise to a maximum at d
5
 except for
anomalous values of Mn and Tc and fall
regularly as the atomic number increases.
They have high enthalpies of atomisation which
are shown in Fig. 4.2.  The maxima at about
the middle of each series indicate that one
unpaired electron per d orbital is particularly
Lattice Structures of Transition Metals
Sc Ti V Cr Mn Fe Co Ni Cu Zn
hcp hcp bcc bcc X bcc ccp ccp ccp X
(bcc) (bcc) (bcc, ccp) (hcp) (hcp) (hcp)
Y Zr Nb Mo Tc Ru Rh Pd Ag Cd
hcp hcp bcc bcc hcp hcp ccp ccp ccp X
(bcc) (bcc) (hcp)
La Hf Ta W Re Os Ir Pt Au Hg
hcp hcp bcc bcc hcp hcp ccp ccp ccp X
(ccp,bcc) (bcc)
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93 The d- and f- Block Elements
favourable for strong interatomic interaction. In general, greater the
number of valence electrons, stronger is the resultant bonding. Since
the enthalpy of atomisation is an important factor in determining the
standard electrode potential of a metal, metals with very high enthalpy
of atomisation (i.e., very high boiling point) tend to be noble in their
reactions (see later for electrode potentials).
Another generalisation that may be drawn from Fig. 4.2 is that the
metals of the second and third series have greater enthalpies of
atomisation than the corresponding elements of the first series; this is an
important factor in accounting for the occurrence of much more frequent
metal – metal bonding in compounds of the heavy transition metals.
Fig. 4.2
Trends in enthalpies
of atomisation of
transition elements
In general, ions of the same charge in a given series show progressive
decrease in radius with increasing atomic number. This is because the
new electron enters a d orbital each time the nuclear charge increases
by unity. It may be recalled that the shielding effect of a d electron is
not that effective, hence the net electrostatic attraction between the
nuclear charge and the outermost electron increases and the ionic
radius decreases. The same trend is observed in the atomic radii of a
given series. However, the variation within a series is quite small. An
interesting point emerges when atomic sizes of one series are compared
with those of the corresponding elements in the other series. The curves
in Fig. 4.3 show an increase from the first (3d) to the second (4d) series
of the elements but the radii of the third (5d) series are virtually the
same as those of the corresponding members of the second series. This
phenomenon is associated with the intervention of the 4f orbitals which
must be filled before the 5d series of elements begin. The filling of 4f
before 5d orbital results in a regular decrease in atomic radii called
Lanthanoid contraction which essentially compensates for the expected
4.3.2 Variation in
Atomic and
Ionic Sizes
of
Transition
Metals
D
a
H
V
/kJ mol
–1
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