Question

trend of enthalpy of atomisation in d block elements and all other factors related to it

Answer 1

The trend of enthalpy of atomisation in d-block elements is generally an increase from left to right across a period up to the middle (e.g., Fe) and then a decrease towards the end (e.g., Zn). Down a group, it generally decreases. This trend is primarily governed by the number of unpaired electrons, which dictates the strength of metallic bonding. Stronger metallic bonding, resulting from more unpaired electrons and efficient orbital overlap, leads to a higher enthalpy of atomisation. Elements with stable electronic configurations (like $d^5$ or $d^{10}$) or fewer unpaired electrons exhibit lower enthalpies of atomisation.

Answer 2

• Definition: Enthalpy of atomisation ($\Delta H_{atom}^\circ$) is the enthalpy change when one mole of a substance in its standard state is converted into gaseous atoms. For metals, it represents the energy required to break the metallic bonds and form gaseous atoms.

• Trend in D-block Elements:

  • Across a Period: Generally, the enthalpy of atomisation increases from left to right across a period up to the middle of the d-block (e.g., Fe, Co, Ni) and then decreases towards the end (e.g., Cu, Zn).
  • Down a Group: The enthalpy of atomisation generally decreases down a group.

• Factors Influencing Enthalpy of Atomisation:

  1. Number of Unpaired Electrons: Unpaired electrons in d-orbitals contribute to stronger metallic bonding through d-d orbital overlap, increasing atomisation enthalpy.
  2. Strength of Metallic Bonding: Stronger metallic bonding, due to extensive electron delocalisation and interatomic forces, leads to higher atomisation enthalpy.
  3. Electronic Configuration: Stable configurations like $d^5$ or $d^{10}$ can influence energy requirements. For instance, Mn ($[Ar] 3d^5 4s^1$) and Zn ($[Ar] 3d^{10} 4s^2$) have relatively lower enthalpies of atomisation due to their stable configurations and fewer unpaired electrons.
  4. Atomic Size and Interatomic Distance: Increasing atomic size down a group leads to weaker metallic bonding and decreased atomisation enthalpy.