Which of the following metals has the strongest metallic bond?

Analyze the question: We need the metal with the strongest metallic bonding among Al, K, Mg and Na.

Concept: Metallic bonding is the electrostatic attraction between positive metal ions (cations) and the "sea" of delocalized electrons. Its strength depends on:

1. Number of valence electrons donated. More delocalized electrons mean a stronger bond.
2. Charge on the cation. A higher charge means stronger attraction.
3. Size of the ion. A smaller radius means a higher charge density and a stronger attraction.

Working:

| Metal | Electron configuration | Valence electrons | Ion | |---|---|---|---| | Na (11) | 2,8,1 | 1 | Na⁺ | | Mg (12) | 2,8,2 | 2 | Mg²⁺ | | Al (13) | 2,8,3 | 3 | Al³⁺ | | K (19) | 2,8,8,1 | 1 | K⁺ |

• Al contributes 3 electrons per atom, giving Al³⁺, which has the highest charge.
• Al³⁺ is also small, so its charge density is very high.
• K is the weakest. It has only 1 valence electron and a large atomic radius (4 shells), so its bond is weak and its metal is soft with a low melting point.

Order of strength: Al > Mg > Na > K

This agrees with the melting points: Al ≈ 660 °C, Mg ≈ 650 °C, Na ≈ 98 °C, K ≈ 63 °C.

Answer: Aluminium (A) has the strongest metallic bond.

Tip: For metals in the same period, the strongest metallic bond belongs to the one with more valence electrons and a smaller radius, so it increases from left to right (Na < Mg < Al). Down a group, metallic bonding gets weaker as atoms get bigger (Na > K).