Sat January 21, 2012 By: Kanwal Sandhu

how is lanthanoid and actinoid contraction different from the general trend of contraction alond any period?

Expert Reply
Sun January 22, 2012
 In lanthanides, the nuclear charge increases by one unit at each successive element and this new electron enters the 4f-subshell. Due to the peculiar shapes of f-orbitals, there is imperfect shielding of electrons from the nuclear attraction. As a result of this the size of lanthanide atoms decreases.
It is different as in lanthanoid contraction the penultimate 4f orbitals are being filled.
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