Question

Explain the meaning of inner transition series. 

OR 

What are inner-transition elements?

Answer 1

i. The last electron in the f-block elements enters into (n-2) f-orbitals, i.e., inner to the penultimate energy level and they form a transition series within the transition series (d-block elements). Hence, the f-block elements are known as inner transition series. 

ii. There are two series of inner transition elements:

a. Lanthanoids (atomic number 58-71) 

b. Actinoids (atomic number 90-103).