The lanthanide contraction is the result of poor shielding of the 4f electrons by inner orbitals. As atomic number increases from La to Lu, the nuclear charge increases and 4f electrons penetrate closer to the nucleus. This causes the atomic and ionic radii to steadily decrease, resulting in smaller sizes down the lanthanide series. Due to the decreasing size, properties like ionization energy and electronegativity increase while chemical reactivity and basicity of hydroxides decrease from La to Lu.

1. LANTHANIDE
CONTRACTION

2. The atomic size or the ionic radii of tri positive lanthanide
ions decrease steadily from La to Lu due to increasing
nuclear charge and electrons entering inner (n-2) f orbital.
This gradual decrease in the size with an
increasing atomic number is called
lanthanide contraction
The lanthanide contraction is the result of a poor
shielding effect of 4f electrons

4. Shielding
cause
contraction?????

5. Shielding effect The inner-shell electrons shield the outer-
shell electrons so they are not effected by nuclear charge
There will be repulsive force between inner and outer electrons which leads
to restrict the penetration of the outer shell towards the nucleus and thus shield
the nucleus charge for outer shell electrons
POOR SHIELDING Positively charge nucleus decreasing the
has greater attraction to electrons atomic radius as the Z
Eu Gd Tb Dy Ho Er Tm
La Ce Pr Nd Pm
Sm
y
b
SIZE DECREASES

6. 5d
6s
4f
nucleus
1
2
3
1
Nucleus charge on f-orbitals is
more
[Attractive force > Repulsive
force]
2
Due to unsymmetrical shape of
f-orbital , it cannot shield the
outer orbitals so, the outer
orbitals also feels nuclear
charge
3
Nucleus force of attraction on
outer electron increases
and therefore it inward towards
the nucleus and cause reduce in
size
Outer shell
Inner shell

9. SEPERATION OF LANTHANIDES
 Since all the elements exhibit the +3 oxidation state as common,
they have similar properties
Thus, the separation of elements in its pure state is difficult.
we use Repeated Fractional Crystallization
[ Ion Exchange method]
Similarities in atomic size of second and third transition series
elements :
Due to lanthanide contraction, the atomic and ionic radius of the
next and before on the lanthanide elements with same group, are
about same.
For examples, the atomic radius of Zr [ group — 4 , period —
5] and Hf [ group — 4 , period — 6] are 160 pm and 159
pm respectively .

10. ELECTRONEGATIVITY
Electronegativity is a measure of the tendency of an atom to attract a
bonding pair of electrons.
The Pauling scale is the most commonly used
La to Lu Electronegativity
IONISATION ENERGY
The amount of energy required to remove an electron from an
isolated atom or molecule
M(g) + IE M+(g) + e
 Due to lanthanide contraction, the force of attraction on the outer shell electrons
will be more which leads to increase the ionization energy.
La to Lu Ionization Energy
A B
𝛿+ 𝛿-

11. BASIC STRENGTH OF HYDROXIDES
 As the size decreases, charge to size ratio increase, the ionic
character decreases or covalent character increases making
hydroxides less and less basic [removal of OH-]
 More the charge to size ratio, the electron cloud of anion is
more polarized, more covalent character [ fajan’s rule]
CHARGE
COVALENT CHARACTER
SIZE

12.  As the size of lanthanides decreases from La to Lu,
the covalent character of the hydroxides increases and hence
their basic strength decreases.
Thus, La (OH)3 is more basic and Lu(OH)3 is the least basic.
La
+3
Lu
+3
3
OH-
3
OH-
Basicity decreases

13. The difference of density between the second and
third transition metal series :
The density of second and third transition metal series are much
more higher due to lanthanide contraction .
Because the atomic volume of two different elements of 4d and
5d series with same group is near about same , but atomic mass
of 5d series elements becomes much higher.
Complex formation
Lanthanides exhibiting 3+ oxidation state is the larger and
hence low charge to radius ratio.
This reduces the complex-forming ability of lanthanides
compared to d-block elements.
 Still they, form complexes with strong chelating agents like
EDTA, β-diketones, oxime etc. They do not form Pπ-complexes

14. The decrease in chemical reactivity of next transition
elements on the lanthanide :
Due to lanthanide contraction, the ionization energy of the next on the
lanthanide elements increases (Ionization energy of 5d elements are much
larger than 4d and 3d. In 5d series, all elements except Pt and Au have filled s-
shell.)
 Hence , their chemical reactivity decreases.
For examples, the chemical reactivity of the element which belong to sixth
period such as, gold ( Au ), platinum ( Pt ), mercury ( Hg ) etc are very much
less.
Mercury – the liquid metal: Mercury is the only metal that exists in its
liquid state at room temperature.
6s valence electrons of Mercury are more closely pulled by the nucleus
(lanthanide contraction) such that outer s-electrons are less involved in metallic
bonding.

15. THANK YOU