Discuss the general characteristics of the 3d series of transition elements with special reference to their:
i) atomic sizes
ii) enthalpies of atomisation
iii) tendency for complex formation
i) atomic sizes
ii) enthalpies of atomisation
iii) tendency for complex formation
Solution
(i) Atomic sizes: the radius decreases over the first few elements (growing nuclear charge), remains almost constant through the middle (added d electrons shield the added charge), and increases slightly toward Cu–Zn (e–e repulsion in the filled shell).
(ii) Enthalpies of atomisation: all are high because both 3d and 4s electrons join the metallic bond; the values peak near the middle of the series where unpaired d electrons are most numerous, and are lowest at Zn.
(iii) Complex formation: very pronounced — the ions are small with high charge density and possess vacant d-orbitals of suitable energy to accept ligand lone pairs, e.g. [Fe(CN)], [Cu(NH)].
(ii) Enthalpies of atomisation: all are high because both 3d and 4s electrons join the metallic bond; the values peak near the middle of the series where unpaired d electrons are most numerous, and are lowest at Zn.
(iii) Complex formation: very pronounced — the ions are small with high charge density and possess vacant d-orbitals of suitable energy to accept ligand lone pairs, e.g. [Fe(CN)], [Cu(NH)].
CBSE Class 12 Board · 2003 · Foreign · Subjective