Class 12 Chemistry D and F Block Elements Actinoids


  • The elements from Th to Lr belong to the series of Actinoids i.e. Actinoids contain 14 elements.
  • They are radioactive elements.
  • The former elements have long half-lives whereas the latter elements have a half-life value ranging from1 day to 3 minutes for lawrencium with atomic number 103.
  • Actinoids have the electronic configuration of 7s2 and inconstant occupancy of the 5f and 6d subshells.
  • Electronic configuration of Thorium is 5f1 6d1 7s2, Am is [Rn] 5f77s2 and Cm
    is [Rn] 5f 76d17s2
  • The ionic radii gradually decrease across the series due to the poor screening effect of nuclear charge exerted by the f electrons. This is called Actinoid contraction.

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