Question

Why Cr has higher melting point than Mn ?

Hint:

Metallic bond strength \(\propto\) number of unpaired electrons participating in the bond. The stable \(d^5\) shell of Mn makes it an anomaly in the melting point trend.

Answer 1

Chromium (Cr) has a higher melting point than Manganese (Mn) due to several factors related to their atomic structure and bonding.
1. Electron Configuration and Bonding:
Chromium has the electron configuration \( [Ar] 3d^5 4s^1 \), which results in a half-filled \( 3d \)-subshell, making it relatively stable. This unique electron arrangement allows for stronger metallic bonding because the d-electrons can delocalize more effectively, leading to stronger interatomic forces. These stronger metallic bonds require more energy to break, thus raising the melting point.
Manganese, on the other hand, has the electron configuration \( [Ar] 3d^5 4s^2 \). While manganese also has a half-filled \( 3d \)-subshell, the additional \( 4s^2 \) electrons result in weaker delocalization of electrons compared to chromium. This results in weaker metallic bonds, lowering the melting point of manganese.
2. Atomic Structure and Packing:
Chromium has a more compact and efficient crystal structure compared to manganese. This tighter packing of atoms results in stronger interatomic forces and a higher melting point. Manganese, being less efficiently packed, experiences weaker interatomic forces.
3. Bonding and Atomic Size:
Chromium has a smaller atomic radius compared to manganese, which contributes to stronger metallic bonding. The closer arrangement of atoms in chromium further strengthens the bonds, leading to a higher melting point. Manganese, with a slightly larger atomic radius, does not have as strong interatomic bonds, resulting in a lower melting point.
Therefore, the higher melting point of chromium compared to manganese can be attributed to stronger metallic bonding, more efficient atomic packing, and a more stable electron configuration.