Class 12 Chemistry D and F Block Elements Introduction to F-block elements

Introduction to F-block elements

  • The elements with gradually filled f orbitals are called f-block elements.
  • The elements of 4f series of the inner transition metals are called lanthanoids whereas the elements of 5f series are called actinoids.


Problem: Actinoid contraction is greater from element to element than lanthanoid contraction. Why?

Solution: In actinoids, 5f orbitals are filled having poorer shielding effect than 4f orbitals (in lanthanoids) due to which the effective nuclear charge experienced by the electrons in valence shells of actinoids is more than what is experienced by lanthanoids. Therefore, the size of contraction in actinoids is greater as compared to that in lanthanoids. They are termed as inner transition elements due to their occurence inside the series of transition elements.

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