Question

The first transition series metal with the highest melting point is

• A. Iron
• B. Vanadium
• C. Chromium
• D. Manganese
• E. Copper

Hint:

Tungsten (W) has the highest melting point of all metals, but among the 3d series, it's Chromium.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
The melting point of transition metals is related to the strength of the metallic bonding. The strength of metallic bonding, in turn, depends on the number of delocalized electrons, which for transition metals includes both the ns and (n-1)d electrons. A greater number of unpaired electrons participating in bonding leads to stronger metallic bonds and a higher melting point.
Step 2: Detailed Explanation
Let's analyze the number of unpaired electrons for the given metals in the first transition series (3d series):

Vanadium (V, Z=23): \([\text{Ar}] 3d^3 4s^2\). It has 3 unpaired d-electrons. All 5 outer electrons can participate in metallic bonding.
Chromium (Cr, Z=24): \([\text{Ar}] 3d^5 4s^1\). It has 6 unpaired electrons (5 in 3d and 1 in 4s). All 6 electrons can participate in strong metallic bonding.
Manganese (Mn, Z=25): \([\text{Ar}] 3d^5 4s^2\). It has 5 unpaired d-electrons. However, Mn has a complex crystal structure, which leads to weaker metallic bonding and an anomalously low melting point compared to its neighbors.
Iron (Fe, Z=26): \([\text{Ar}] 3d^6 4s^2\). Pairing starts in the d-orbital. It has 4 unpaired d-electrons.
Copper (Cu, Z=29): \([\text{Ar}] 3d^{10} 4s^1\). It has only 1 unpaired electron in the 4s orbital available for bonding.
The strength of metallic bonding generally increases up to the middle of the series and then decreases as the d-electrons start to pair up. Chromium has the maximum number of unpaired electrons (6) available for metallic bonding. This results in the strongest interatomic forces and consequently the highest melting point among the elements of the first transition series.
Step 3: Final Answer
Chromium has the highest melting point in the first transition series due to having the maximum number of unpaired electrons contributing to strong metallic bonding.