Out of Cr and Mn, which have higher melting point?

Cr

The correct answer is option 1. \(Cr\).

Let us explore why chromium \((Cr)\) has a higher melting point than manganese \((Mn)\) by examining their atomic structure, bonding, and crystal lattice:

Atomic Structure and Bonding:

1. Chromium (Cr):

Atomic number: 24

Electron configuration: \([Ar] 3d_5 4s^1\)

Chromium has six valence electrons (five in the 3d orbital and one in the 4s orbital), which participate in metallic bonding. The presence of multiple unpaired d-electrons strengthens the metallic bonds.

2. Manganese (Mn):

Atomic number: 25

Electron configuration: \([Ar] 3d_5 4s_2\)

Manganese has seven valence electrons (five in the 3d orbital and two in the 4s orbital). Despite having more valence electrons, the complexity of the crystal structure in manganese reduces the effectiveness of these electrons in contributing to metallic bonding.

Crystal Structure:

1. Chromium (Cr):

Chromium crystallizes in a body-centered cubic (bcc) structure. This simple and symmetrical structure allows for efficient packing and strong metallic bonds throughout the crystal lattice.

2. Manganese (Mn):

Manganese has a more complex crystal structure with several allotropes. The most stable form at room temperature is α-Mn, which has a complex cubic structure with 58 atoms per unit cell. This complexity leads to weaker metallic bonding compared to the bcc structure of chromium.

Metallic Bonding:

Strength of Metallic Bonds:

In transition metals, the strength of metallic bonding depends on the number of unpaired d-electrons available for bonding and the efficiency of atomic packing in the crystal lattice.

Chromium, with its simple bcc structure and multiple unpaired d-electrons, forms stronger metallic bonds compared to manganese.

Melting Points:

Chromium (Cr): Has a melting point of approximately 1907°C (3465°F).

Manganese (Mn): Has a melting point of approximately 1246°C (2275°F).

Conclusion:

Chromium has a higher melting point than manganese due to its stronger metallic bonding and more efficient crystal packing. The simpler bcc structure of chromium allows for stronger interactions between atoms, resulting in a higher melting point. In contrast, the complex structure of manganese leads to weaker metallic bonding, resulting in a lower melting point.

Therefore, the correct answer is: Cr