Introduction to F-block elements
0 The elements with gradually filled f
orbitals are called f-block elements.
0 The elements of 4f series of the inner
transition metals are called lanthanoids
whereas the elements of 5f series are
called actinoids.
••block
1A p-block M
i--1~ 2A 3A 4A 5A 6A 7A ls•
~ 25 ... -- 2p -
d-block
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~
3p L
. .
'4- 45 : - 3d -
~
4p L
i-t- 55 : --
.
4d -
~
Sp L
- . -. 6p .
~ 65 :. 5d
~ 75 :- - 6d
f-block
-- 4f . L
- 5f L
Problem: Actinoid contraction is greater
from element to element than lanthanoid
contraction. Why?
Solution: In actinoids, 5f orbitals are filled
having poorer shielding effect than 4f
orbitals (in lanthanoids) due to which the
effective nuclear charge experienced by the
electrons in valence shells of actinoids is
more than what is experienced by
lanthanoids. Therefore, the size of
contraction in actinoids is greater as
compared to that in lanthanoids. They are
termed as inner transition elements due to
their occurence inside the series of
transition elements.
Lanthanoid:
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Lanthanides
0 The electronic Configuration of
lanthanoid is [Xe] 4fn+1 5d 6s 2 or [Xe]
0
4fn 5d 1 6s 2 with their valence shell
electronic configuration as 4f1- 14 6s 2.
0 They exhibit the oxidation state of +3,
+2 and +4.
0 The initial members of this series are
somewhat reactive towards calcium
which resembles their behaviour to that
of aluminum with the gradual
increasing atomic number.
0 On application of gentle heat
Lanthanides combine with hydrogen.
0 Heating them with carbon leads to the
formation of carbides and halides (in
presence of halogens while burning).
0 Reaction of Lanthanides with dilute
acids releases hydrogen gas.
Lanthanoid contraction:
0 As we move along the lanthanoid series,
the atomic number gradually increases
by one or we can say number of
electrons and protons increases by one.
0 Addition of electrons to the same shell
increases the effective nuclear charge.
0 Increase in atomic numb er also1
increases the number of electrons in
the 4f orbital having poor shielding
effect due to which the effective nuclear
charge upon the outer electrons also
.
increases.
0 Therefore the size of lanthanoids
steadily decreases with the increase in
the atomic number and phenomenon is
called lanthanoid
0 As a result of lanthanoid contraction
there is a sim1ilarity in the properties of
second and third transition series.
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Lanthanides Decrease in atomic size 7
Oxidation States of lanthanoids
0 The elements belonging to lanthanide
series exhibit an oxidation state of +3.
For example, Praseodymium (Pr) shows
+3 oxidation state.
0 Some elements exhibit +2 oxidation
states in their complexes in solutions.
For example, Samarium (Sm), Europium
(Eu), Thulium (Tm) and Ytterbium (Yb)
show +2 oxidation state.
0 Some elements exhibit +4 oxidation
states due to high stability of empty,
half-filled or fully filled f-subshells.
0 Praseodymium (Pr), Neodymium (Nd),
Terbium (Tb) and Dysprosium (Dy)
exhibits +4 oxidation state in their
oxides.
° Cerium (Ce) shows both +3 as well as
+4 state.
Actinoids
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Actinides
0 The elements f ram Th to Lr belong to
the series of Actinoids i.e. Actinoids
contain 14 elements.
0 They are radioactive elements.
0 The former elements have long half-
lives whereas the latter elements have a
half-life value ranging from1 day to 3
minutes for lawrencium with atomic
number 103.
0 Actinoids have the electronic
configuration of 7s 2 and inconstant
occupancy of the 5f and 6d subshells.
0 Electronic configuration of Thorium is
5f 1 6d 1 7s 2, Am is [Rn] 5f77s 2 and Cm
is [Rn] 5f 76d 17s 2
0 Actinoids have the electronic
configuration of 7s 2 and inconstant
occupancy of the Sf and 6d subshells.
0 Electronic configuration of Thorium is
5f 1 6d 1 7s 2, Am is [Rn] 5f77s 2 and Cm
is [Rn] 5f 76d 17s2
0 The ionic radii gradually decrease
across the series due to the poor
screening effect of nuclear charge
exerted by the f electrons. This is called
Actinoid contraction.
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Actinides Decrease in atomic size across the series --->
Oxidation state in Actinoids
o In general the oxidation state of these
elements is +3 (similar to lanthanides).
o They also exhibit +4 oxidation states.
o Some of the elements also exhibit
higher oxidation states.
o The oxidation state initially rises to the
middle of the series (+4 for Th to +5, +6
and+7 for Pa, V and Np) and then
descends in the succeeding elements.
ARRlications of d- and f-Block elements
o Iron and steels are used for making
tools, utensils, vehicles, bridges and
much more.
0 TiO for the pigment industry and Mn0 2
for use in dry battery cells.
0 Zn and Ni/Cd is also used for battery
industry.
0 Elements of Group 11 called the
coinage metals.
0 V20 5 catalyses the oxidation of S0 2 in
the manufacture ofsulphuric acid.
0 TiCl 4 with A1(CH 3) 3 forms the basis of
the Ziegler catalystsused to
manufacture polyethylene (polythene).
0 Iron catalysts are used inthe Haber
process for the production of ammonia
from N2/H 2 mixtures.
0 Nickel catalysts enable the
hydrogenation of fats
o Wackerprocess the oxidation of ethyne
to ethanal is catalysed by PdCl 2.
o Nickel useful in the polymerisation of
alkynes and other organiccompounds
such as benzene.
o The photographic industry relies on
thespecial light-sensitive properties of
Ag Br.
Problem: Write down the electronic
configuration of:
(i) Cr3+ (iii) cu+ (v) Co 2+ (vii) Mn 2+
(ii) Pm 3+ (iv) Ce 4+ (vi) Lu 2+ (viii) Th 4+
Solution:
(i) Cr3+: 1s2 2s2 2p6 3s2 3p 6 3d3
Or, [Ar] 183d3
(ii) Pm 3+: 1s2 2s2 2p6 3s2 3p 6 3d10 4s2 4p 6
4d10 5s2 5p6 4f4
Or, [Xe] 54 3d3
(iii) cu+: 1s2 2s2 2p6 3s2 3p6 3d10
Or, [Ar] 18 3d1o
(iv) Ce 4+: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
4d10 5s2 5p6
Or, [Xe] 54
(v) Co 2+: 1s2 2s2 2p6 3s2 3p6 3d7
(v) 2 2 2 6 2 6
Co +: 1s 2s 2p 3s 3p 3d7
Or, 18
[Ar] 3d7
(vi) 2 2 2 6 2 6 10 2
Lu +: 1s 2s 2p 3s 3p 3d 4s 4p 6
4d10 ss2 Sp 6 4f14 Sd1
54 14 3
Or, [Xe] 2f 3d
2 2 2 6 2 6 5
(vii) Mn +: 1s 2s 2p 3s 3p 3d
Or, [Ar] 18
3d 5
