Question

Give reasons:

The enthalpies of atomization of transition metals of 3d series do not follow a regular trend throughout the series.

Answer 1

1. Enthalpies of atomization depend on the strength of metallic bonding, which is influenced mainly by the number of unpaired d-electrons. Initially, with increasing atomic number, unpaired electrons increase up to d⁵ configuration, strengthening bonds and increasing enthalpy.
2. Beyond d⁵, electrons start pairing up, reducing the number of unpaired electrons and weakening metallic bonds. This irregular increase and decrease in unpaired electrons causes irregular trends in enthalpy.
3. Some metals, like manganese and technetium, show lower enthalpies due to complicated lattice structures, affecting bonding strength.
4. Factors like atomic size, nuclear charge, and electron configurations also contribute to uneven bonding strength and so irregular atomization enthalpies across the 3d series.

Thus, the combination of changing unpaired electron numbers and structural differences causes the irregular trend in the enthalpies of atomization of 3d transition metals.