Tendency to form complexes in lanthanides

1.	Tendency to form complexes in lanthanides
Answer» It is observed that in lanthanide series, there is a progressive decrease in the ATOMIC and ionic RADII with INCREASING atomic number . This REGULAR decrease with increase in atomic number is called lanthanide contraction. This is due to the weak shielding of f orbitals. These f orbitals are UNABLE to counter balance the effect of increasing nuclear charge because of which the size keeps on decreasing with increase in atomic number.

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