What is an lanthanoid contraction ? What is its cause ? Give its consequences .

What is an lanthanoid contraction ? What is its cause ? Give its consequences .
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Ans The decrease in atomic and ionic size with increase in atomic no. in lanthanoid series is called lanthanoid contraction . The cause of lanthanoid contraction is poor shielding effect of d and f electron , due to which effective nuclear charge increases . . consequences :- (i) The ion ic size of lanthanoid is similar to each other , they occur , together and their separation becomes difficult . (ii) The ionization energy of 5 d – transition series are higher than 4 d – transition series . (iii)There is close resemblance between elements of 4 d and 5 d transition series . due to similar ionic 
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