Question

The transition metal with the highest melting point is ________.

• A. Mo
• B. Mn
• C. W
• D. Cr
• E. Au

Hint:

Tungsten (W) is used in bulb filaments specifically because of its record-high melting point.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
The melting point of a metal is determined by the strength of its metallic bonds. For transition metals, the strength of these bonds is primarily related to the number of delocalized electrons, particularly the unpaired d-electrons, that can participate in bonding. This question asks to identify the metal with the highest melting point from the given list, which requires knowledge of periodic trends.
Step 2: Key Formula or Approach
The general trends for melting points of transition metals are:
- Across a period, the melting point tends to increase towards the middle of the series (where the number of unpaired d-electrons is maximal) and then decrease.
- Down a group, the melting point generally increases due to stronger metallic bonding involving higher-energy, more diffuse valence orbitals.
Step 3: Detailed Explanation
1. Analyze the position of the elements in the periodic table:
- Cr (Chromium), Mo (Molybdenum), and W (Tungsten) are all in Group 6. Their order down the group is Cr \(\to\) Mo \(\to\) W.
- Mn (Manganese) is in Group 7.
- Au (Gold) is in Group 11.
2. Apply the periodic trends:
- The melting point generally reaches a maximum around Group 6, where elements have a large number of valence electrons (\(ns^1(n-1)d^5\)) available for metallic bonding.
- Following the trend down Group 6, the strength of metallic bonding increases. This is due to the increasing size of the d-orbitals (3d<4d<5d), which leads to more effective overlap and stronger bonds. Therefore, the melting point increases in the order Cr<Mo<W.
- Tungsten (W) is known to have the highest melting point of all pure metals (3422 \(^\circ\)C or 3695 K). This is due to its half-filled d-subshell and the large radial extension of its 5d orbitals, leading to very strong metallic bonding.
- Manganese (Mn) has an anomalously low melting point compared to its neighbors because of its complex crystal structure and the stability of its half-filled \(d^5\) shell, which reduces electron delocalization.
- Gold (Au) has a filled d-shell (\(d^{10}s^1\)), which leads to weaker metallic bonding compared to the elements in the middle of the transition series.
3. Conclusion:
Based on the trends, Tungsten (W) has the strongest metallic bonds and therefore the highest melting point among the given options.
Step 4: Final Answer
The transition metal with the highest melting point is W (Tungsten).