F-BLOCK ELEMENTS POWER POINT PRESENTATIONS

F BLOCK ELEMENTS
DR.M.PRASHANTHI
ASSISTANT PROFESSOR
DEPARTMENT OF CHEMISTRY
GDCW, KARIMNAGAR.

F-BLOCK ELEMENTS
The elements in which the outermost
electrons enter the f sub-shell
They belong to the 6th and 7th periods.
They are placed separately at the
bottom of the periodic table.

INNER TRANSITION ELEMENTS
The elements which have partly tilled (n-2) f-
orbitals are f-block elements.
Since their inner subshells (4f and 5f) are
successively filled with electrons, these
electrons are called inner transition elements.
There are two series of inner transition elements.
They are
Lanthanide series (4f-block elements)
Actinide series (5f-block elements)

The elements in which the additional electrons
enters (n-2) f-orbitals are called inner transition
elements.
The valence shell electronic configuration of these
elements can be represented as
(n 2)f
‒ 0-14
(n – 1)d0-1
ns2
4f inner transition metals are known as
lanthanides because they come immediately
after Lanthanum.
5f inner transition metals are known as actinides
because they come immediately after Actinium.

PROPERTIES OF F BLOCK ELEMENTS
These metals are soft with moderate
densities of about 7gcm-3.
They have high melting points.
They are quite reactive similar to the alkali
metals than d block metals.
Common oxidation state for lanthanides is
+3.
+2 is also very common among these ,
higher o.s like +4 is unusual(except-Ce).

LANTHANIDES
Also called as Rare earth elements,
because it was difficult to extract them
economically from their ores.

LANTHANIDES
A group of 14 elements after lantanum (Z=58)
constitutes lanthanide series.
Characteristic properties of lanthanides
Electronic configuration:
Lanthanides have 4f2-14 5d0-1 6s2 ionic
configuration.
Oxidation states: The principal oxidation state of
lanthanides is +3.
In the case of La, Gd and Lu, removal of three electrons
yield stable 4f0, 4f7 and 4f14 configuration.

On moving across the lanthanide series, the nuclear
charge increases by +1 at each step and the
addition of extra electron takes place in
Colour and spectra: Some of the trivalent lanthanide
ions having partly filled f-orbitals are coloured in
the solid states well as in aqueous solution.
The colour appears to depend upon the number of f-
electrons in 4f orbital.

Oxidation potential: Lanthanides have high
oxidation potentials.Thus, they have a strong
tendency to lose their electrons to undergo
oxidation.
They are strong reducing agents
They show strong electropositive character

Properties
Lanthanides have lower heat of atomization
than transition metals.
The energy required to break up the metal
lattice is heat of atomization.
This is because with d-electrons, transition
metals are much harder and require high heat
of atomization.
Europium and ytterbium have the lowest
enthalpies of vaporization and largest atomic
radii of lanthanides and resemble Barium.

Lanthanide contraction
Definition: The atomic and ionic size usually
decrease from left to right across a period.
This is due to increase in effective nuclear charge
(Z*) which pulls the orbital electrons closer to the
nucleus.
Cause of Lanthanide contraction: In lanthanide
atoms and ions, the 4f orbital is filled
successively from Ce to Lu.
In general, the shielding effect of electrons
decreases in the order ns > np > nf.
Expression.
Z* = Z – S

Atomic and ionic sizes: The Lanthanide
Contraction
As the atomic number increases , each
succeeding element contains one more
electron in the 4f -orbital and one proton in the
nucleus.
The 4f electrons are ineffective in screening the
outer electrons from the nucleus causing
imperfect shielding.
As a result , nucleus attraction for the outer
electrons gradually increases and
consequently gradual decrease in size occur.
This is called lanthanide contraction.

Consequences of Lanthanide
Contraction
There is close resemblance between 4d and
5d transition series.
Ionization energy of 5d transition series is
higher than 3d and 4d transition series.

Consequence of lanthanide contraction
Due to the close similarity in electronic configuration the
lanthanides have identical chemical properties.
The lanthanide contraction also explains the
decreasing basicity of the lanthanides.
Certain pairs of elements such as Zr/Hf, Nb/Ta and Mo/W have
almost idential size against the expected size increase due to
increased atomic numbers.
This is a direct consequence of lanthanide contraction.
Difficulty in separation of lanthanides

ATOMIC RADII
Across the period the radii decreases as the size
decreases.
The decrease in lanthanides is very steady, this is
called the Lanthanide contraction
As we move left to right the nuclear charge
increases by +1 and an electron is added.
The electron is added to the same 4f subshell.
Due to their diffused shape the 4f electrons shield
each other poorly from the nuclear charge.
With increasing atomic number the effective nuclear
charge increases thus pulling the 4f shell closer,
causing it to contract.

RADII
Their ionic radii decrease from 117 pm
of La to 100 pm for Lu.
This is because 5f orbitals do not shield
the outer 5s and 5p electrons
effectively, leading to increase in
effective
nuclear charge and decrease in the
ionic size.

REACTIONS WITH LN
All the lanthanides form hydroxides of
the general formula Ln (OH)3
These are ionic and basic.
Since the ionic size decreases from
La3+
to Lu3+
the basicity of hydroxides
decreases.
La(OH)3 is the strongest base while
Lu(OH)3 is the weakest base.

Basic character
Lanthanides form trivalent ionic compounds. For
example, their hydroxides.
Ln(OH)3 is ionic and basic in character. They are
stronger bases than Al(OH)3.
Complex formation: The lanthanide ions have
low charge / size ratio, as compared to that of
transition elements.
They cannot, therefore, cause much polarization
and consequently, they have poor tendency to
form complexes.

ELECTRONIC CONFIGURATION
General electronic configuration of
lanthanides is represented as
[Xe] 4f 0-14
5d 0-1
6s2
Xe = Xenon, Z= 54
The E.C for Xe is
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s2
4d10

EXCEPTIONS
The electrons first fill up the 6s 4f and 5d are
very close in energy.
In case of lanthanum the 5d orbital has lower
energy.
In case of Gd and Yb the anamolous behavior
is observed as half filled and fully filled
electrons have extra stability.
Thus general E.C for lanthanides is
[Xe] 4f 0-14
5d 0-1
6s2

IONIZATION ENTHALPY
As size increases, ionization enthalpy
decreases since the last electron
experiences lesser pull from the
nucleus
Across the period, size decreases thus
I.E increases.

Ionization Enthalpies
Fairly low I. E
First ionization enthalpy is around 600 kJ mol-1,
the second about 1200 kJ mol-1 comparable
with those of calcium.
Due to low I. E, lanthanides have high
electropositive character.

COLOUR IN LANTHANIDES
These elements are coloured due to the
f-f transitions which corresponds to the
energy in the visible spectrum
The colour of ions with nf electrons is-
(14-n)f electrons

Coloured ions
Many of the lanthanide ions are coloured in
both solid and in solution due to f – f transition
since they have partially filled f – orbitals.
Absorption bands are narrow, probably
because of the excitation within f level.
La3+
and Lu3+
ions do not show any colour
due to vacant and fully filled f- orbitals.

OXIDATION STATE
General electronic configuration is
[Xe] 4f 0-14
5d 0-1
6s2
,thus the common o.s is +3
i.e. 2 e- from 6s and the other from d/f sub shell
The 4f electrons are shielded by the inner 5s and
5p orbitals, they are tightly bond to the nucleus.
Thus they do not take part in the bonding.
Some show O.S +2 and +4, due to f 0
, f 7
, f 14
Electronic configuration.

Oxidation States
Predominantly +3 oxidation state.
+3 oxidation state in La,Gd,Lu are especially stable
(Empty half filled and Completely filled f-sub shell
respectively).
Ce and Tb shows +4 oxidation state(Ce4+
- 4fo
&Tb4+
-4f7
).
Occasionally +2 and +4 ions in solution or in solid
compounds are also obtained.
This irregularity arises mainly from the extra stability of
empty, half filled or filled f –sub shell.

The most stable oxidation state of lanthanides
is +3.
Hence the ions in +2 oxidation state tend to
change +3 state by loss of electron acting as
reducing agents.
The ions in +4 oxidation state tend to change to
+3 oxidation state by gain of electron acting
as a good oxidizing agent in aqueous
solution.

SHIELDING EFFECT
The decrease in the net force of attraction
between the electrons present in the
outer shell of an atom in the direction of
nucleus due to change in linearity of the
electric lines of forces between them
due to the presence of high election
density in the inner shells in the same
atom is known as screening effect.

Magnetic properties
The lanthanide ions other than the f0
type(La3+
andCe3+
)
and the f14
type (Yb2+
and Lu3+
) are all paramagnetic.
The paramagnetism rises to the maximum in
neodymium.
Lanthanides have very high magnetic susceptibilities
due to their large numbers of unpaired f-electrons.
The La3+ (4f0), Ce4+(4f0), Yb2+ (4f14) and Lu3+ (4f14) ions
have all the electrons paired and hence they are
diamagnetic.

Magnetic moment
μ=√n(n + 2) BM
n = no. of unpaired electrons
Calculate magnetic moment for La3+
La -57
[Xe] 4f0
5d1
6s2
n=1
—————

Properties
Silvery white soft metals, tarnish in air rapidly.
Hardness increases with increasing atomic
number, Samarium being steel hard.
Good conductor of heat and electricity.
Promethium is radioactive.

Separation of Lanthanides
Fractional crystallisation method
The separation of lanthanide ions by this method is based on
the slight differences in solubility.
Fractional precipitation method
The differences in stability of lanthanide complexes is the
basic principle of this method
Solvent extraction method
This method works on the slight difference in the partition
coefficients of the salts of lanthanides between water and
an organic solvent.
Ion exchange method
This is the most elegant for lanthanide separation. It is based
on the principle of selective exchange of lanthanide ions
with the H+
ion of a cation exchange resin.

Chemical Properties
Metal combines with hydrogen when gently
heated in the gas.
The carbides, Ln3C, Ln2C3 and LnC2 are formed
when the metals are heated with carbon.
They liberate hydrogen from dilute acids and
burn in halogens to form halides.
They form oxides and hydroxides, M2O3 and
M(OH)3, basic like alkaline earth metal oxides
and hydroxides.

W
i
t
h
a
c
i
d
s
With
helogens
Heated with S Ln
Heated
with
N
2
B
u
r
n
w
i
t
h
O
2
C 2773
K
W
ith
H
2O
Ln2S
3
Ln
N
LnC
2
Ln(OH)3
+H2
LnX
3
H
2
Ln2
O3

Applications of Lanthanides
In hybrid cars, superconductors and permanent
magnets
Used in the colour tubes of computers and T.V’s
since they produce visible light over a small
wavelength upon bombarding with electrons.
(Eu,Y)2O3 – red colour
Their types of Ln are used to get 3 primary
colours
Luminescent materials Nd: YAG laser

ACTINIDES
Starts with Thorium Z=90 and ends with
Lawrencium Z=103
They are all radioactive and man-made and
have high M.P, B.P and density.
The electronic configuration of actinides is
[Rn] 5f 0-14
6d 0-2
7s 2
, where Rn is the electronic
configuration of radon.
Most stable oxidation state in actinides is +3.
The actinides show a variety of O.S from +2 to
+8

Actinides
The 14 elements from Th (z=90) to Lw (z=103) are
characterised by the progressive filling up of the
5f-orbitals.
They constitute the actinide series.
Characteristic Properties of Actinides
Electronic configuration:
The 5f block elements (actinides) have (n-2)f1-14 (n-1)
d1 ns2 configuration analogous to lanthanides.

Metallic nature:Like the lanthanides, actinides are all
metals.
Oxidation states: Unlike lanthanides, the
actinides have no character oxidation state.
Colour: Actinides cations having unpaired 5f
electrons are coloured in the solid as well as in
aqueous solution.
Actinide contraction: Like the lanthanides,
actinides show the phenomenon of actinide
contraction.
Magnetic properties: Like the lanthanides,
actinides are strongly paramagnetic.

OXIDATION STATE
Early lanthanides show variable O.S this is similar to
transition elements than lanthanides
This pattern is seen mostly due to the ability of 5f orbital to
participate in bonding
A ready loss of 5f electrons by early actinides indicates
that these electrons are much closer in energy to 7s and
6d electrons than the 4f electrons to 6s and 5d electrons
as in lanthanides
G.E.C [Rn] 5f 0-14
6d 0-2
7s 2
E.g.. Uranium has electronic configuration of
[Rn]7s2
5f3
6d1
.
The formation of +6 oxidation state corresponds to an
electronic configuration of [Rn].

ACTINIDE CONTRACTION
5f 6d 7s are almost same energy in actinides.
The 7s electrons shield the 5f and 6d orbitals
from nuclear charge,thus they expand a little.
Therefore, they have size greater than
lanthanides.
But the decrease in radii is not as prominent,
due to the shielding effect of f- orbitals.

APPLICATIONS OF ACTINIDES
Half lives of Thorium & Uranium are so long that
the amount of radiation emitted is negligible, thus
they can be used in everyday life.
Th (IV) oxide, ThO2 with 1% CeO2 was used as a
major source of indoor lighting before incandescent
lamps came into existence.
These oxides convert heat energy from burning
natural gas to an intense light.

POST ACTINIDE ELEMENTS
Elements with atomic number greater than 92 are called
‘Transuranium’.
Elements from atomic number 93 to 103 now are included
in actinide series and those from 104 to 118 are called as
post actinide elements.
They are included as postactinoids because similar to
actinide elements, they can be synthesized in the nuclear
reactions.
So far, nine post actinide elements have been synthesized.
Half life is in seconds 2.8 x 10^-4, thus difficult to study
reactions
Rutherfordium forms a chloride, RfCl4, similar to zirconium
and hafnium in the +4 oxidation state.
Dubnium resembles to eboth, group 5 transition metal,
niobium(V) and actinid, protactinium(V).

Transuranic elements
Elements lying beyond uranium i.e. beyond atomic
number 92 are called transuranic elements (Z =
93- 103). These are radioactive elements
produced through nuclear reactions.
Neptunium: It was prepared by Wahi and Seaborg in
1942 by the action of high speed neutrons on U –
238.
Plutonium: Plutonium – 239 is a very important
isotope in nuclear chemistry.It is produced on a
large scale (from natural uranium) by the action of
slow neutrons on U – 238.
Americium: It is prepared by bombarding Pu – 239
with alpha particles.

The Actinides
All isotopes are radioactive, with only 232Th,
235U, 238U and 244Pu having long half-lives.
Only Th and U occur naturally,both are more
abundant in the earth’s crust than Tin.
The others must be made by nuclear
processes.

oxidation state
The dominant oxidation state of actinides is +3.
Actinides also exhibit an oxidation state of +4.
Some actinides such as Uranium, Neptunium
and plutonium also exhibit an oxidation state
of +6.
The actinides show actinide contraction (like
lanthanide contraction) due to poor shielding
of the nuclear charge by 5f electrons.
All the Actinides are radioactive in nature.

Actinide Contraction
The size of atoms / M3+
ions decreases
regularly along actinide series.
The steady decrease in ionic/ atomic radii with
increase in atomic number is called Actinide
Contraction.
The contraction is greater from element to
element in this series, due to poor shielding
effect by 5-f electron.

Magnetic Properties
Paramagnetic behavior
Magnetic properties are more complex than
those of lanthanides.
M.P and B.P
High M.P and B.P
Do not follow regular gradation of M.P or B.P
with increase in atomic number.

IONISATION ENTHALPY
Low I.E. so electropositiity is high.
COLOUR
Generally coloured. Colour depends up on the
number of 5f electrons
The ions containing 5fo and 5f7are colourless
E.g. – U3+ (5f 3 ) – Red
Np3+ (5f 4 ) – Bluish

Comparison of Lanthanides and Actinides
Similarities
Both show +3 oxidation state
In both the cases, f-orbitals of (n-2) shell are progressively
filled up
A contraction in atomic and ionic size is observed in both
the cases (lanthanide and actinide contractions)
Both lanthanides and actinides show sharp line-like
absorption spectra due to f-f transition
They have low electronegativity values
These elements are quite reactive
These elements form coloured ions
Their nitrates, perchlorates and sulphates in the +3 state are
soluble in water.
Their hydroxides and carbonates in +3 state are insoluble in
water.
Members of both the series show ion exchange behaviour

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