Question

Which element of the 3d series has the lowest enthalpy of atomisation and why?

Hint:

The enthalpy of atomisation is lower for elements with stable electron configurations, such as copper's \( 3d^{10} \), as less energy is required to break the bonds.

Answer 1

To address this problem, the objective is to identify the 3d series element with the lowest enthalpy of atomisation and provide the rationale for this observation.

1. Understanding Enthalpy of Atomisation:
Enthalpy of atomisation quantifies the energy necessary to transform one mole of a solid metal into its gaseous atomic state. This property is intrinsically linked to the strength of metallic bonds, which is, in turn, governed by the number of unpaired electrons available for delocalisation within the metallic lattice structure.

2. Identifying the 3d Series Elements:
The elements constituting the 3d series are Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. A comparative analysis of their electronic configurations and resultant bonding strengths is required.

3. Analysis of Electronic Configurations:
- Sc: \( [Ar] 3d^1 4s^2 \), possessing 1 unpaired d-electron.
- Ti: \( [Ar] 3d^2 4s^2 \), with 2 unpaired electrons.
- V: \( [Ar] 3d^3 4s^2 \), exhibiting 3 unpaired electrons.
- Cr: \( [Ar] 3d^5 4s^1 \), featuring 6 unpaired electrons (the maximum observed).
- Mn: \( [Ar] 3d^5 4s^2 \), having 5 unpaired electrons.
- Fe: \( [Ar] 3d^6 4s^2 \), with 4 unpaired electrons.
- Co: \( [Ar] 3d^7 4s^2 \), showing 3 unpaired electrons.
- Ni: \( [Ar] 3d^8 4s^2 \), possessing 2 unpaired electrons.
- Cu: \( [Ar] 3d^{10} 4s^1 \), with 1 unpaired electron.
- Zn: \( [Ar] 3d^{10} 4s^2 \), demonstrating 0 unpaired electrons (a fully filled configuration).

4. Correlation with Metallic Bonding:
A direct correlation exists between the strength of metallic bonding (determined by the number of unpaired electrons available for delocalisation) and the enthalpy of atomisation; stronger bonding leads to a higher enthalpy. Zinc (Zn), with its completely filled \( 3d^{10} 4s^2 \) electronic configuration, lacks unpaired d-electrons for delocalisation. This deficiency results in weaker metallic bonding when compared to other elements in the 3d series.

5. Comparison of Enthalpy Values:
Empirical data substantiates that Zn exhibits the lowest enthalpy of atomisation, approximately 130 kJ/mol. Conversely, elements such as Cr (~397 kJ/mol) and V (~515 kJ/mol) display significantly higher values due to their greater number of unpaired electrons.

Final Answer:
Zinc (Zn) records the lowest enthalpy of atomisation within the 3d series. This is attributable to its complete \( 3d^{10} 4s^2 \) electronic configuration, which precludes the presence of unpaired d-electrons for delocalisation, thereby leading to attenuated metallic bonding.