Question

What do you understand by lanthanide contraction? Write the general electronic configuration of the inner transition element?

Answer 1

Hint : Lanthanides are the $15$ rare –earth metals or chemical species present in the periodic table. Lanthanides start from the atomic number $58{\text{ to 71}}$ , following the element Lanthanum. These elements are present in very small quantities in the earth’s atmosphere.

Complete Step By Step Answer:
To solve this question, we need to have some basic knowledge regarding the periodic table.
So lanthanides or lanthanide series are present in the group $6$of the periodic table starting from the atomic number$58{\text{ to 71}}$.
So, lanthanide contraction is the phenomenon in which atomic radii of the lanthanides decrease on increasing the atomic number. Thus, we can say that the atomic radii of the elements of the lanthanides series decreases as we move from left to right in the row.
Lanthanide belongs to the $f -$ series of the periodic table. These are also known as inner – transition elements.
Now, we have enough knowledge to rule out electronic configuration.
Hence, we can say – Electronic configuration for the lanthanide series is -
${[Xe]_{54{\text{ }}}}4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$
So, this is the general electronic configuration of the lanthanide series.

Note :
Also, lanthanides have similar chemical properties and this is due to the fact because lanthanides have similar outer configuration. In the compounds, lanthanides are present in the $+ 3$ oxidation states. Also, these are soft metals and present in low quantities and have high boiling and melting points. One more interesting fact about them is that they all are colourless and this is because they have partially filled $f$orbitals.