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.
8
UnitUnit
UnitUnit
Unit
8
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216Chemistry
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 8.1.
In general the electronic configuration of outer orbitals 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. 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 8.1.
8.18.1
8.18.1
8.1
Position in thePosition in the
Position in thePosition in the
Position in the
Periodic TablePeriodic Table
Periodic TablePeriodic Table
Periodic Table
8.28.2
8.28.2
8.2
ElectronicElectronic
Electronic
Electronic
Electronic
ConfigurationsConfigurations
ConfigurationsConfigurations
Configurations
of the d-Blockof the d-Block
of the d-Blockof the d-Block
of the d-Block
ElementsElements
ElementsElements
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: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
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217 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 8.1Example 8.1
Example 8.1Example 8.1
Example 8.1
SolutionSolution
SolutionSolution
Solution
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