NCERT Textbook - The D & F block elements Class 12 Notes | EduRev

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Class 12 : NCERT Textbook - The D & F block elements Class 12 Notes | EduRev

 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 elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block 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 three series of the transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg,  omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, a transition element is defined as
the one which has incompletely filled d orbitals in its
ground state or in any one of its oxidation states. 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 three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms sets the study of the transition elements and
The The The The The d d d d d- and - and - and - and - and f f f f f- - - - -
Block Element Block Element Block Element Block Element Block Elements s s s s
The The The The The d- d- d- d- d- and and and and and f- f- f- f- f-
Block Element Block Element Block Element Block Element Block Elements s s s s
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.
8
Unit Unit Unit Unit Unit
8
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 elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block 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 three series of the transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg,  omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, a transition element is defined as
the one which has incompletely filled d orbitals in its
ground state or in any one of its oxidation states. 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 three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms sets the study of the transition elements and
The The The The The d d d d d- and - and - and - and - and f f f f f- - - - -
Block Element Block Element Block Element Block Element Block Elements s s s s
The The The The The d- d- d- d- d- and and and and and f- f- f- f- f-
Block Element Block Element Block Element Block Element Block Elements s s s s
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.
8
Unit Unit Unit Unit Unit
8
210 Chemistry
their compounds apart from that of the main group
elements. However, the usual theory of valence as
applicable to the main group elements can also be
applied successfully to the transition elements.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium form part of the transition metals.
In this Unit, besides introduction, we shall first deal
with the electronic configuration, occurrence and general
characteristics of the transition elements with special
emphasis on the trends in the properties of the first
row (3d) transition metals and 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 flanked by s– and
p– blocks in the periodic table. The very name ‘transition’ given to the
elements of d-block is only because of their position between s– and
p– block elements. The d–orbitals of the penultimate energy level in
their atoms receive electrons giving rise to the three rows of the transition
metals, i.e., 3d, 4d and 5d. The fourth row of 6d is still incomplete.
These series of the transition elements are shown in Table 8.1.
In general the electronic configuration of these elements is
(n-1)d
1–10
ns
1–2
. 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. Consider the case of Cr,
for example, which has 3d
5 
4s
1
 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 outer electronic configurations of the
transition elements are given in Table 8.1.
8.1 8.1 8.1 8.1 8.1 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
8.2 8.2 8.2 8.2 8.2 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 8.1: Outer Electronic Configurations of the Transition Elements (ground state)
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 elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block 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 three series of the transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg,  omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, a transition element is defined as
the one which has incompletely filled d orbitals in its
ground state or in any one of its oxidation states. 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 three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms sets the study of the transition elements and
The The The The The d d d d d- and - and - and - and - and f f f f f- - - - -
Block Element Block Element Block Element Block Element Block Elements s s s s
The The The The The d- d- d- d- d- and and and and and f- f- f- f- f-
Block Element Block Element Block Element Block Element Block Elements s s s s
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.
8
Unit Unit Unit Unit Unit
8
210 Chemistry
their compounds apart from that of the main group
elements. However, the usual theory of valence as
applicable to the main group elements can also be
applied successfully to the transition elements.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium form part of the transition metals.
In this Unit, besides introduction, we shall first deal
with the electronic configuration, occurrence and general
characteristics of the transition elements with special
emphasis on the trends in the properties of the first
row (3d) transition metals and 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 flanked by s– and
p– blocks in the periodic table. The very name ‘transition’ given to the
elements of d-block is only because of their position between s– and
p– block elements. The d–orbitals of the penultimate energy level in
their atoms receive electrons giving rise to the three rows of the transition
metals, i.e., 3d, 4d and 5d. The fourth row of 6d is still incomplete.
These series of the transition elements are shown in Table 8.1.
In general the electronic configuration of these elements is
(n-1)d
1–10
ns
1–2
. 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. Consider the case of Cr,
for example, which has 3d
5 
4s
1
 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 outer electronic configurations of the
transition elements are given in Table 8.1.
8.1 8.1 8.1 8.1 8.1 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
8.2 8.2 8.2 8.2 8.2 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 8.1: Outer Electronic Configurations of the Transition Elements (ground state)
211 The d- and f- Block Elements
The electronic configurations of Zn, Cd and Hg 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 project 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 affecting 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 horizontal similarities in the properties of the
transition elements in contrast to the main group 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 Uub
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 8.1 Example 8.1 Example 8.1 Example 8.1 Example 8.1
Solution Solution Solution Solution Solution
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 elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block 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 three series of the transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg,  omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, a transition element is defined as
the one which has incompletely filled d orbitals in its
ground state or in any one of its oxidation states. 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 three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms sets the study of the transition elements and
The The The The The d d d d d- and - and - and - and - and f f f f f- - - - -
Block Element Block Element Block Element Block Element Block Elements s s s s
The The The The The d- d- d- d- d- and and and and and f- f- f- f- f-
Block Element Block Element Block Element Block Element Block Elements s s s s
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.
8
Unit Unit Unit Unit Unit
8
210 Chemistry
their compounds apart from that of the main group
elements. However, the usual theory of valence as
applicable to the main group elements can also be
applied successfully to the transition elements.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium form part of the transition metals.
In this Unit, besides introduction, we shall first deal
with the electronic configuration, occurrence and general
characteristics of the transition elements with special
emphasis on the trends in the properties of the first
row (3d) transition metals and 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 flanked by s– and
p– blocks in the periodic table. The very name ‘transition’ given to the
elements of d-block is only because of their position between s– and
p– block elements. The d–orbitals of the penultimate energy level in
their atoms receive electrons giving rise to the three rows of the transition
metals, i.e., 3d, 4d and 5d. The fourth row of 6d is still incomplete.
These series of the transition elements are shown in Table 8.1.
In general the electronic configuration of these elements is
(n-1)d
1–10
ns
1–2
. 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. Consider the case of Cr,
for example, which has 3d
5 
4s
1
 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 outer electronic configurations of the
transition elements are given in Table 8.1.
8.1 8.1 8.1 8.1 8.1 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
8.2 8.2 8.2 8.2 8.2 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 8.1: Outer Electronic Configurations of the Transition Elements (ground state)
211 The d- and f- Block Elements
The electronic configurations of Zn, Cd and Hg 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 project 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 affecting 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 horizontal similarities in the properties of the
transition elements in contrast to the main group 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 Uub
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 8.1 Example 8.1 Example 8.1 Example 8.1 Example 8.1
Solution Solution Solution Solution Solution
212 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
8.1 Silver atom has completely filled d orbitals (4d
10
) in its ground state.
How can you say that it is a transition element?
8.3.1 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.
8.3 8.3 8.3 8.3 8.3 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)
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)
Lattice Structures of Transition Metals
(bcc = body centred cubic; hcp = hexagonal close packed;
ccp = cubic close packed; X = a typical metal structure).
Fig. 8.1: Trends in melting points of
transition elements
The transition metals (with the exception
of Zn, Cd and Hg) are very much hard and
have low volatility. Their melting and boiling
points are high.  Fig. 8.1 depicts the melting
points of the 3d, 4d and 5d transition metals.
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. 8.2.  The maxima at about
the middle of each series indicate that one
unpaired electron per d orbital is particularly
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 elements constituting the f -block are those in
which the 4 f and 5 f orbitals are progressively filled
in the latter two long periods; these elements are formal
members of group 3 from which they have been taken
out to form a separate f-block 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 three series of the transition
metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5d
series (La to Hg,  omitting Ce to Lu). The fourth 6d
series which begins with Ac is still incomplete. The two
series of the inner transition metals, (4f and 5f) are
known as lanthanoids and actinoids respectively.
Strictly speaking, a transition element is defined as
the one which has incompletely filled d orbitals in its
ground state or in any one of its oxidation states. 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 three transition series, their chemistry is studied
along with the chemistry of the transition metals.
The presence of partly filled d or f orbitals in their
atoms sets the study of the transition elements and
The The The The The d d d d d- and - and - and - and - and f f f f f- - - - -
Block Element Block Element Block Element Block Element Block Elements s s s s
The The The The The d- d- d- d- d- and and and and and f- f- f- f- f-
Block Element Block Element Block Element Block Element Block Elements s s s s
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.
8
Unit Unit Unit Unit Unit
8
210 Chemistry
their compounds apart from that of the main group
elements. However, the usual theory of valence as
applicable to the main group elements can also be
applied successfully to the transition elements.
Various precious metals such as silver, gold and
platinum and industrially important metals like iron,
copper and titanium form part of the transition metals.
In this Unit, besides introduction, we shall first deal
with the electronic configuration, occurrence and general
characteristics of the transition elements with special
emphasis on the trends in the properties of the first
row (3d) transition metals and 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 flanked by s– and
p– blocks in the periodic table. The very name ‘transition’ given to the
elements of d-block is only because of their position between s– and
p– block elements. The d–orbitals of the penultimate energy level in
their atoms receive electrons giving rise to the three rows of the transition
metals, i.e., 3d, 4d and 5d. The fourth row of 6d is still incomplete.
These series of the transition elements are shown in Table 8.1.
In general the electronic configuration of these elements is
(n-1)d
1–10
ns
1–2
. 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. Consider the case of Cr,
for example, which has 3d
5 
4s
1
 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 outer electronic configurations of the
transition elements are given in Table 8.1.
8.1 8.1 8.1 8.1 8.1 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
8.2 8.2 8.2 8.2 8.2 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 8.1: Outer Electronic Configurations of the Transition Elements (ground state)
211 The d- and f- Block Elements
The electronic configurations of Zn, Cd and Hg 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 project 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 affecting 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 horizontal similarities in the properties of the
transition elements in contrast to the main group 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 Uub
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 8.1 Example 8.1 Example 8.1 Example 8.1 Example 8.1
Solution Solution Solution Solution Solution
212 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
8.1 Silver atom has completely filled d orbitals (4d
10
) in its ground state.
How can you say that it is a transition element?
8.3.1 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.
8.3 8.3 8.3 8.3 8.3 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)
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)
Lattice Structures of Transition Metals
(bcc = body centred cubic; hcp = hexagonal close packed;
ccp = cubic close packed; X = a typical metal structure).
Fig. 8.1: Trends in melting points of
transition elements
The transition metals (with the exception
of Zn, Cd and Hg) are very much hard and
have low volatility. Their melting and boiling
points are high.  Fig. 8.1 depicts the melting
points of the 3d, 4d and 5d transition metals.
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. 8.2.  The maxima at about
the middle of each series indicate that one
unpaired electron per d orbital is particularly
213 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. 8.2 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. 8.2
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. 8.3 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
8.3.2 Variation in
Atomic and
Ionic Sizes
of
Transition
Metals
D
a
H
V
/kJ mol
–1
Read More
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