(a) Give three points of difference between lanthanoids and actinoids.
(b) Give a reason and select the one atom/ion which will exhibit the asked property:
i) Sc³⁺ or Cr³⁺ (exhibits diamagnetic behaviour)
ii) Cr or Cu (high melting and boiling point)
(b) Give a reason and select the one atom/ion which will exhibit the asked property:
i) Sc³⁺ or Cr³⁺ (exhibits diamagnetic behaviour)
ii) Cr or Cu (high melting and boiling point)
Solution
(a) Differences:
(b)(i) Sc: configuration [Ar]3d — no unpaired electron, hence diamagnetic (Cr, 3d, is paramagnetic).
(ii) Cr: with 3d4s it has six unpaired/bonding electrons — the strongest metallic bonding of the pair — so chromium has the high melting and boiling points (Cu, 3d4s, has no unpaired d electrons).
- Lanthanoids fill 4f orbitals; actinoids fill 5f.
- Lanthanoids show essentially only +3; actinoids show +3 up to +7 (near-degenerate 5f/6d/7s).
- Lanthanoids (except promethium) are non-radioactive; all actinoids are radioactive.
(b)(i) Sc: configuration [Ar]3d — no unpaired electron, hence diamagnetic (Cr, 3d, is paramagnetic).
(ii) Cr: with 3d4s it has six unpaired/bonding electrons — the strongest metallic bonding of the pair — so chromium has the high melting and boiling points (Cu, 3d4s, has no unpaired d electrons).
CBSE Class 12 Board · 2022 · Subjective