Ionic bond and lattice energy
Chemical Bonding (Basics) · Chemistry
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Study notes
Why does MgO melt at 2852°C but NaCl at only 801°C? Step 1: Lattice energy U ∝ (q⁺ × q⁻)/r. Step 2: NaCl: charges 1+ and 1−; MgO: 2+ and 2− → 4× charge product. Step 3: Mg²⁺ and O²⁻ are also smaller than Na⁺ and Cl⁻. Step 4: U(MgO) ≈ 3795 kJ/mol vs U(NaCl) ≈ 787 kJ/mol → far stronger lattice, far higher mp. Charge dominates lattice strength.