Question

The number of valence electrons present in the metal among Cr, Co, Fe, and Ni which has the lowest enthalpy of atomisation is

• A. 8
• B. 9
• C. 6
• D. 10

Hint:

In general, for transition metals, a lower number of valence electrons leads to weaker metallic bonding, hence a lower enthalpy of atomisation.

Answer 1

The Correct Option is C

Step 1: Atomic Configuration and Valence Electrons
Chromium (Cr):
Atomic number = 24. Electron configuration: \([ \text{Ar} ] 3d^5 4s^1\). Valence electrons: 6.
Cobalt (Co):
Atomic number = 27. Electron configuration: \([ \text{Ar} ] 3d^7 4s^2\). Valence electrons: 9.
Iron (Fe):
Atomic number = 26. Electron configuration: \([ \text{Ar} ] 3d^6 4s^2\). Valence electrons: 8.
Nickel (Ni):
Atomic number = 28. Electron configuration: \([ \text{Ar} ] 3d^8 4s^2\). Valence electrons: 10.
Step 2: Relation to Enthalpy of Atomisation
Enthalpy of atomisation typically decreases with an increase in valence electrons due to stronger metallic bonding requiring more energy to break. Therefore, fewer valence electrons correlate with lower enthalpy of atomisation. As Cr has 6 valence electrons, it exhibits the lowest enthalpy of atomisation among Cr, Co, Fe, and Ni.
Consequently, the correct answer is 6 valence electrons.