Question

What are lanthanides? Give the various oxidation states of lanthanides.

Answer 1

Hint: These are rare earth elements having incomplete penultimate and pre-penultimate shells. These elements due to incomplete inner orbitals show variable oxidation state and similar chemical property.

Complete step by step solution:
Lanthanides are those elements which have unfilled penultimate and pre-penultimate shells.
The lanthanide series comprises 15 metallic elements.
In the periodic table, we will see that the lanthanide series starts from element lanthanum having atomic number 57 up to element lutetium having atomic number 71.
They are called lanthanides because the elements in this series are chemically similar to element lanthanum which is a d-block element.
The general electronic configuration of lanthanide series is $\left[ {{\text{ }}Xe} \right]4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$.
We will find out that all elements of the lanthanide series show similar chemical properties due to its 4f orbital buried deep inside ions and atoms due to which electrons present in the 4f orbital could not interact with surrounding and exhibit remarkably similar chemical properties.
Due to incomplete inner shells, elements of lanthanide series show variable oxidation states which are +2, +3 and +4. Out of all, +3 is the most stable oxidation state of lanthanides.
Also, one of the most peculiar features which lanthanides show is Lanthanide Contraction which is the result of poor shielding effect of electrons present in 4f orbitals of lanthanides.

Note: It should be remembered that due to lanthanoid contraction, elements of 4d and 5d series have comparable size.
Electrons present in 4f orbitals show poor shielding effect.
Lanthanides are also used as alloys to impart strength and hardness to metals.