Question

Write electronic configuration of Cr (Z = 24) and Cu (Z = 29) and also explain two main characteristics of transition elements.

Hint:

Always check for exceptional cases (Cr, Cu, Mo, Ag, etc.) where half-filled or fully-filled \(d\)-orbitals provide extra stability.

Answer 1

Step 1: Electronic configuration of Cr (Z = 24).
The expected configuration is: \[ \text{Cr: } [Ar] \, 3d^4 \, 4s^2 \] But due to extra stability of half-filled orbitals, the actual configuration is: \[ \text{Cr: } [Ar] \, 3d^5 \, 4s^1 \] Step 2: Electronic configuration of Cu (Z = 29).
The expected configuration is: \[ \text{Cu: } [Ar] \, 3d^9 \, 4s^2 \] But due to extra stability of fully filled orbitals, the actual configuration is: \[ \text{Cu: } [Ar] \, 3d^{10} \, 4s^1 \] Step 3: Two main characteristics of transition elements.
\begin{enumerate} \item
Variable oxidation states: Transition metals exhibit multiple oxidation states due to the involvement of both \(3d\) and \(4s\) electrons in bonding. \item
Formation of coloured compounds: Due to the presence of partially filled \(d\)-orbitals, they show \(d \rightarrow d\) electronic transitions which give rise to characteristic colours. \end{enumerate} Conclusion:
Chromium and copper show exceptional electronic configurations due to stability of half-filled and fully-filled \(d\)-orbitals. Transition elements are unique for their variable oxidation states and coloured compounds.