Q60 / 180 · COMEDK 2024 (Afternoon Shift) · Chemistry
The correct order of increasing melting point is
- A$\mathrm{Cr}<\mathrm{Ti}<\mathrm{V}<\mathrm{Mn}$
- B$\mathrm{V}<\mathrm{Ti}<\mathrm{Mn}<\mathrm{Cr}$
- C$\mathrm{Ti}<\mathrm{V}<\mathrm{Cr}<\mathrm{Mn}$
- Correct answerD$\mathrm{Mn}<\mathrm{Ti}<\mathrm{V}<\mathrm{Cr}$
Solution
The melting points of transition metals depend on the strength of metallic bonding, which is related to the number of unpaired electrons available for delocalization in the metallic lattice. The electronic configurations of the given elements are:
$\mathrm{Ti} (3d^{2} 4s^{2})$
$\mathrm{V} (3d^{3} 4s^{2})$
$\mathrm{Cr} (3d^{5} 4s^{1})$
$\mathrm{Mn} (3d^{5} 4s^{2})$
Generally, the melting point increases as the number of unpaired electrons increases, reaching a maximum at the middle of the series. However, $\mathrm{Mn}$ has a stable half-filled $d$-subshell ($3d^{5}$), which makes its electrons less available for metallic bonding compared to its neighbors. This leads to a significantly lower melting point for $\mathrm{Mn}$ compared to $\mathrm{Cr}$, $\mathrm{V}$, and $\mathrm{Ti}$.
The melting points of these elements are approximately:
$\mathrm{Mn} \approx 1246 \, \mathrm{K}$
$\mathrm{Ti} \approx 1941 \, \mathrm{K}$
$\mathrm{V} \approx 2183 \, \mathrm{K}$
$\mathrm{Cr} \approx 2180 \, \mathrm{K}$
Comparing these values, the order of increasing melting point is $\mathrm{Mn} < \mathrm{Ti} < \mathrm{V} < \mathrm{Cr}$.
Answer: $\mathrm{Mn}<\mathrm{Ti}<\mathrm{V}<\mathrm{Cr}$
$\mathrm{Ti} (3d^{2} 4s^{2})$
$\mathrm{V} (3d^{3} 4s^{2})$
$\mathrm{Cr} (3d^{5} 4s^{1})$
$\mathrm{Mn} (3d^{5} 4s^{2})$
Generally, the melting point increases as the number of unpaired electrons increases, reaching a maximum at the middle of the series. However, $\mathrm{Mn}$ has a stable half-filled $d$-subshell ($3d^{5}$), which makes its electrons less available for metallic bonding compared to its neighbors. This leads to a significantly lower melting point for $\mathrm{Mn}$ compared to $\mathrm{Cr}$, $\mathrm{V}$, and $\mathrm{Ti}$.
The melting points of these elements are approximately:
$\mathrm{Mn} \approx 1246 \, \mathrm{K}$
$\mathrm{Ti} \approx 1941 \, \mathrm{K}$
$\mathrm{V} \approx 2183 \, \mathrm{K}$
$\mathrm{Cr} \approx 2180 \, \mathrm{K}$
Comparing these values, the order of increasing melting point is $\mathrm{Mn} < \mathrm{Ti} < \mathrm{V} < \mathrm{Cr}$.
Answer: $\mathrm{Mn}<\mathrm{Ti}<\mathrm{V}<\mathrm{Cr}$
Hence, the correct answer is option: 'D'.