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Class XII
Chemistry
Chapter 8
The d and f-Block Elements
Top Concepts
1. d -Block elements: The elements lying in the middle of periodic table
belonging to groups 3 to 12 are known as d – block elements. Their
general electronic configuration is (n – 1)d1-10 ns1-2 where (n – 1)
stands for penultimate (last but one) shell.
2. Transition element: 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.
3. Zinc, cadmium, mercury are not regarded as transition metals due to
completely filled d – orbital.
4. f-Block elements: 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.
5. Lanthanoids: The 14 elements immediately following lanthanum, i.e.,
Cerium (58) to Lutetium (71) are called lanthanoids. They belong to
first inner transition series. Lanthanum (57) has similar properties.
Therefore, it is studied along with lanthanoids.
6. Actinoids: The 14 elements immediately following actinium (89), with
atomic numbers 90 (Thorium) to 103 (Lawrencium) are called
actinoids. They belong to second inner transition series. Actinium (89)
has similar properties. Therefore, it is studied along with actinoids.
7. Four transition series:
a. 3d – transition series. The transition elements with atomic
number 21(Sc) to 30(Zn) and having incomplete 3d orbitals is
called the first transition series.
b. 4d – transition series. It consists of elements with atomic
number 39(Y) to 48 (Cd) and having incomplete 4d orbitals. It is
called second transition series.
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c. 5d – transition series. It consists of elements with atomic
number 57(La), 72(Hf) to 80(Hg) having incomplete 5d orbitals.
It is called third transition series.
d. 6d – transition series. It consists of elements with atomic
number 89(Ac), 104(Rf) to 112(Uub) having incomplete 6d
orbitals. It is called fourth transition series.
8. General Characteristics of transition elements:
a. Metallic character: All transition elements are metallic in nature,
i.e. they have strong metallic bonds. This is because of presence
of unpaired electrons. This gives rise to properties like high
density, high enthalpies of atomization, and high melting and
boiling points.
b. Atomic radii: The atomic radii decrease from Sc to Cr because
the effective nuclear charge increases. The atomic size of Fe,
Co, Ni is almost same because the attraction due to increase in
nuclear charge is cancelled by the repulsion because of increase
in shielding effect. Cu and Zn have bigger size because the
shielding effect increases and electron electron repulsions
repulsion increases.
c. Lanthanoid Contraction: The steady decrease in the atomic and
ionic radii of the transition metals as the atomic number
increases. This is because of filling of 4f orbitals before the 5d
orbitals. This contraction is size is quite regular. This is called
lanthanoid contraction. It is because of lanthanoid contraction
that the atomic radii of the second row of transition elements
are almost similar to those of the third row of transition
elements.
d. Ionisation enthalpy: There is slight and irregular variation in
ionization energies of transition metals due to irregular variation
of atomic size. The I.E. of 5d transition series is higher than 3d
and 4d transition series because of Lanthanoid Contraction.
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1
Class XII
Chemistry
Chapter 8
The d and f-Block Elements
Top Concepts
1. d -Block elements: The elements lying in the middle of periodic table
belonging to groups 3 to 12 are known as d – block elements. Their
general electronic configuration is (n – 1)d1-10 ns1-2 where (n – 1)
stands for penultimate (last but one) shell.
2. Transition element: 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.
3. Zinc, cadmium, mercury are not regarded as transition metals due to
completely filled d – orbital.
4. f-Block elements: 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.
5. Lanthanoids: The 14 elements immediately following lanthanum, i.e.,
Cerium (58) to Lutetium (71) are called lanthanoids. They belong to
first inner transition series. Lanthanum (57) has similar properties.
Therefore, it is studied along with lanthanoids.
6. Actinoids: The 14 elements immediately following actinium (89), with
atomic numbers 90 (Thorium) to 103 (Lawrencium) are called
actinoids. They belong to second inner transition series. Actinium (89)
has similar properties. Therefore, it is studied along with actinoids.
7. Four transition series:
a. 3d – transition series. The transition elements with atomic
number 21(Sc) to 30(Zn) and having incomplete 3d orbitals is
called the first transition series.
b. 4d – transition series. It consists of elements with atomic
number 39(Y) to 48 (Cd) and having incomplete 4d orbitals. It is
called second transition series.
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c. 5d – transition series. It consists of elements with atomic
number 57(La), 72(Hf) to 80(Hg) having incomplete 5d orbitals.
It is called third transition series.
d. 6d – transition series. It consists of elements with atomic
number 89(Ac), 104(Rf) to 112(Uub) having incomplete 6d
orbitals. It is called fourth transition series.
8. General Characteristics of transition elements:
a. Metallic character: All transition elements are metallic in nature,
i.e. they have strong metallic bonds. This is because of presence
of unpaired electrons. This gives rise to properties like high
density, high enthalpies of atomization, and high melting and
boiling points.
b. Atomic radii: The atomic radii decrease from Sc to Cr because
the effective nuclear charge increases. The atomic size of Fe,
Co, Ni is almost same because the attraction due to increase in
nuclear charge is cancelled by the repulsion because of increase
in shielding effect. Cu and Zn have bigger size because the
shielding effect increases and electron electron repulsions
repulsion increases.
c. Lanthanoid Contraction: The steady decrease in the atomic and
ionic radii of the transition metals as the atomic number
increases. This is because of filling of 4f orbitals before the 5d
orbitals. This contraction is size is quite regular. This is called
lanthanoid contraction. It is because of lanthanoid contraction
that the atomic radii of the second row of transition elements
are almost similar to those of the third row of transition
elements.
d. Ionisation enthalpy: There is slight and irregular variation in
ionization energies of transition metals due to irregular variation
of atomic size. The I.E. of 5d transition series is higher than 3d
and 4d transition series because of Lanthanoid Contraction.
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