Lanthanoid contraction is caused due to - Vidyadip

MCQ

Lanthanoid contraction is caused due to

A
the same effective nuclear charge from $Ce$ to $Lu$
✓
the imperfect shielding on outer electrons by $4f$ electrons from the nuclear charge
C
the appreciable shielding on outer electrons by $4f$ electrons from the nuclear charge
D
the appreciable shielding on outer electrons by $5d$ electrons from the nuclear charge

✓

Answer

Correct option: B.

the imperfect shielding on outer electrons by $4f$ electrons from the nuclear charge

b
The main reason of lanthanide contraction is, poor shielding of $4f$ electrons on the outer most shell electrons. As $f$ orbital is defused nature so shielding of $4$f electron is imperfect that is why nucleus can attract outer most shell electron easily and the size of atom decreases.

In lanthanides, there is poorer shielding of $5 d$ electrons by $4f$ electrons resulting in greater attraction of the nucleus over $5d$ electrons and reduction of the atomic radii.

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