How do you account for the following?
i) All scandium salts are white.
ii) The first ionisation energies of the 5d transition elements are higher than those of the 3d and 4d transition elements in their respective groups.
i) All scandium salts are white.
ii) The first ionisation energies of the 5d transition elements are higher than those of the 3d and 4d transition elements in their respective groups.
Solution
(i) Scandium in its salts exists as Sc with the configuration [Ar]3d. With no d-electrons there can be no d–d transitions, so no visible light is absorbed — scandium salts are white (colourless).
(ii) The 5d elements follow the lanthanoids: their atoms are unexpectedly small (lanthanoid contraction) while the nuclear charge has risen by 14 units that the 4f electrons shield poorly. The higher effective nuclear charge binds the valence electrons more firmly, so IE(5d) > IE(3d, 4d) in each group.
(ii) The 5d elements follow the lanthanoids: their atoms are unexpectedly small (lanthanoid contraction) while the nuclear charge has risen by 14 units that the 4f electrons shield poorly. The higher effective nuclear charge binds the valence electrons more firmly, so IE(5d) > IE(3d, 4d) in each group.
CBSE Class 12 Board · 2003 · Delhi · Subjective