Question

The radii (metallic) of $Fe,Co$ and Ni are nearly same. This is due to

• A. lanthanide contraction
• B. the fact that successive addition 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)

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