Concept:In metallic lattices, melting point is determined by the electrostatic attraction between the positive metal ions and the delocalized sea of valence electrons. The distance between the nucleus and the delocalized electrons weakens this bond.
Solution:- As we move down Group I-A (like Na) or Group II-A (like Mg), new electron shells are added, causing an increment in atomic size.
- The larger the atomic radius, the further the positive nucleus is from the delocalized valence electrons.
- This increased distance weakens the metallic bonding force.
- Weaker metallic bonds require less thermal energy to break, leading to a gradual decrease in melting points down the group.
Why other options are incorrect:- Option A, C, & D: Electronegativity, attractive forces, and ionization energy all decrease down the group, so they cannot be the active cause; strong attractive forces would actually increase the melting point.
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