Question

The radii (metallic) of Fe,Co and Ni are nearly same.

This is due to:

• A. Lanthanide contraction
• B. The fact that successive additions of d–electrons screen the outer electrons (4s) from the inward pull of the nucleus.
• C. Increase in radii due to increase in 'n' is compensated by decrease in radii due to increase in effective nuclear charge (Z).
• D. Atomic radii do not remain constant but decrease in a normal gradation.

Answer 1

Answer: (B)

The fact that successive additions of d–electrons screen the outer electrons (4s) from the inward pull of the nucleus.

Answer 2

After mid way i.e. after Cr as the electrons enters the last but one shell, the added d-electron shields the outer most electrons. Hence with the increase in the d-electrons screening effect increases. This counter balances the increased nuclear charge. As a result, the atomic radii remain practically same after chromium.