Question

How are inner transition elements classified?

Answer 1

1. Inner transition elements are those in which the differentiating electron enters the (n − 2) f-subshell.
2. They form the f-block of the periodic table, placed separately at the bottom.
3. They are divided into two series:
   1. Lanthanoid series: Filling of 4f orbitals, includes 14 elements from Cerium (Ce, Z = 58) to Lutetium (Lu, Z = 71).
   2. Actinoid series: Filling of 5f orbitals, includes 14 elements from Thorium (Th, Z = 90) to Lawrencium (Lr, Z = 103).
4. Both series follow lanthanum (La) and actinium (Ac), respectively, and resemble them in properties.
5. All inner transition elements are metals and are known as rare earth elements due to their rarity in the Earth’s crust.