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LANTHANIDE CONTRACTION (GRADE 12)


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. 





CAUSE OF LANTHANIDE CONTRACTION:

As we move along the period from left to right in lanthanide series, the atomic number increases that is number of protons keeps on increasing. For every proton added in the nucleus the extra electron goes to the same 4f orbital. 

The 4f orbital shows poor shielding effect because of which there is a gradual increase in effective nuclear charge experienced by the outer electrons. Thus, the attraction of the nucleus for the electrons in the outermost shell increases with atomic number.


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