Question

The actinide contraction is due to:

• A. perfect shielding of $5f$ election
• B. imperfect shielding of $4f$ election
• C. imperfect shielding of $5f$ electron
• D. perfect shielding of $4f$ election

Answer 1

The correct option is C imperfect shielding of $5f$ electron

The actinide contraction is due to imperfect shielding of $5f$ electron. The valence shell electronic configuration of actinoids is $5f^{1-14}6d^{0-1}7s^2$. With an increase in atomic number, the positive charge on the nucleus increases by $+1$, and one more electron enters in the same $5f$ subshell.

There is imperfect shielding of one electron by another electron in the same $5f$ subshell. Due to this, the atomic and ionic radii show a gradual decrease with an increase in atomic number.