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Objectives The dd-- and f-
f-
8
After studying this Unit, you will be
able to Block Elements
• learn the positions of the d– and
f-block elements in the periodic
table;
Iron, copper, silver and gold are among the transition elements that
• know the electronic configurations have played important roles in the development of human civilisation.
of the transition (d-block) and the The inner transition elements such as Th, Pa and U are proving
inner transition (f-block) elements; excellent sources of nuclear energy in modern times.
• appreciate the relative stability of
various oxidation states in terms
of electrode potential values; The d-block of the periodic table contains the elements
• describe the preparation, of the groups 3-12 in which the d orbitals are
properties, structures and uses progressively filled in each of the four long periods.
of some important compounds The f-block consists of elements in which 4 f and 5 f
such as K2Cr2O7 and KMnO4; orbitals are progressively filled. They are placed in a
• understand the general separate panel at the bottom of the periodic table. The
characteristics of the d– and names transition metals and inner transition metals
f–block elements and the general are often used to refer to the elements of d-and
horizontal and group trends in f-blocks respectively.
them; There are mainly four series of the transition metals,
• describe the properties of the 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La
f-block elements and give a and Hf to Hg) and 6d series which has Ac and elements
comparative account of the from Rf to Cn. The two series of the inner transition
lanthanoids and actinoids with metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as
respect to their electronic lanthanoids and actinoids respectively.
configurations, oxidation states
and chemical behaviour.
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
10
mercury of group 12 have full d 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
2022-23
, 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)
8.1 Position in the The d–block occupies the large middle section of the periodic table
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
8.2 Electronic 1– 10 1–2
is (n-1)d ns except for Pd where its electronic configuration is 4d105s0.
Configurations The (n–1) stands for the inner d orbitals which may have one to ten
of the d-Block electrons and the outermost ns orbital may have one or two electrons.
However, this generalisation has several exceptions because of very
Elements 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,
5 1 4 2
which has 3d 4s configuration instead of 3d 4s ; 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 3d104s1 and not 3d94s2. The ground state electronic
configurations of the outer orbitals of transition elements are given in
Table 8.1.
Table 8.1: Electronic Configurations of outer orbitals of the Transition Elements
(ground state)
1st Series
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
Chemistry 216
, 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
The electronic configurations of outer orbitals of Zn, Cd, Hg and Cn
10 2
are represented by the general formula (n-1)d ns . 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
n
surrounding them. In some respects, ions of a given d 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.
On what ground can you say that scandium (Z = 21) is a transition Example 8.1
element but zinc (Z = 30) is not?
On the basis of incompletely filled 3d orbitals in case of scandium atom
1
Solution
in its ground state (3d ), it is regarded as a transition element. On the
10
other hand, zinc atom has completely filled d orbitals (3d ) in its
ground state as well as in its oxidised state, hence it is not regarded
as a transition element.
217 The d- and f- Block Elements
2022-23
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