a) Write the electronic configuration of the element with atomic number 102.
b) What is lanthanoid contraction? What is its effect on the chemistry of the elements which follow the lanthanoids?
b) What is lanthanoid contraction? What is its effect on the chemistry of the elements which follow the lanthanoids?
Solution
(a) Z = 102 (nobelium):
(b) Lanthanoid contraction: the steady decrease in atomic/ionic radii across La → Lu, caused by imperfect shielding of nuclear charge by 4f electrons.
Effect on the post-lanthanoid elements: the expected size increase from the 4d to the 5d series is cancelled — Zr ≈ Hf, Nb ≈ Ta, Mo ≈ W in radius. Each 4d/5d pair therefore has almost identical properties, occurs together in nature and is very difficult to separate.
(b) Lanthanoid contraction: the steady decrease in atomic/ionic radii across La → Lu, caused by imperfect shielding of nuclear charge by 4f electrons.
Effect on the post-lanthanoid elements: the expected size increase from the 4d to the 5d series is cancelled — Zr ≈ Hf, Nb ≈ Ta, Mo ≈ W in radius. Each 4d/5d pair therefore has almost identical properties, occurs together in nature and is very difficult to separate.
CBSE Class 12 Board · 2006 · All India · Subjective