7.0 Lanthanoid Series

  d and f Block Elements

• The group of $14$ elements from cerium $(Z=58)$ to Latetium $(Z=71)$ in which last i.e.,differentiating electrons is entering in pre-penultimate $4f$ are called lanthanoids or lanthanides or lanthanones.

• These elements are nominated as lanthanoids from the element lanthanum which is the prototype of lanthanoids.

• Their $(n-2)$ i.e., $4f$ and $(n-1)d$ i.e., $5d$ subshells are incomplete and have general electronic configuration $4{f^{1 - 14}}5{d^{0 - 1}}6{s^2}$.