Account for the following:
a. Ti(IV) is more stable than the Ti (II) or Ti(III).
b. In case of transition elements, ions of the same charge in a given series show progressive decrease in radius with increasing atomic number.
c. Zinc is a comparatively a soft metal, iron and chromium are typically hard.
(a) Ti is having electronic configuration [Ar] 3d2 4s2. Ti (IV) is more stable as Ti4+ acquires nearest noble gas configuration on loss of 4 e-.
(b) In case of transition elements, ions of the same charge in a given series show progressive decrease in radius with increasing atomic number.
As the new electron enters a d orbital each time the nuclear charge increases by unity. The shielding effect of a d electron is not that effective, hence the net electrostatic attraction between the nuclear charge and the outermost electron increases and the ionic radius decreases.
(c) Iron and Chromium are having high enthalpy of atomization due to the presence of unpaired electrons, which accounts for their hardness. However, Zinc has low enthalpy of atomization as it has no unpaired electron.
Hence, zinc is comparatively a soft metal.