Actinide Contraction

  • Atomic and ionic size

As the atomic number increases, the atomic size increases and  effective nuclear charge also increases which attracts the outermost shell more effectively. So, as we move left to right means from actinium to lawrencium in the actinide series, there is gradual decrease in the the atomic or ionic radii with increase in atomic number. This steady decrease I atomic size is called actinide contraction. The actinide contraction is analog to the lanthanide contraction.

Cause of Actinide contraction

The main reason of the actinide contraction is the imperfect shielding of the one 5f-electron by another 5f- electron in the same shell. Due to poor shielding effect of the 5f electrons, effective nuclear charge increases which causes the contraction in atomic size.  When one electron is added to the 5f-orbital every time means proton keeps on increasing due to which the nuclear charge increases irregularly which causes the  poor shielding effect.

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