# Explain why the lattice enthalpy of magnesium chloride (MgCl₂) is significantly more exothermic than that of sodium chloride (NaCl).

> IB DP Chemistry Higher Level (2023 syllabus) — S2.1 The ionic model · Explain · 4 marks

> Lattice enthalpy is a measure of the strength of ionic bonding in a crystalline solid and depends on the charges and sizes of the ions present.

## Mark scheme (4 marks)

1. Magnesium ion (Mg²⁺) carries a 2+ charge whereas sodium ion (Na⁺) carries only a 1+ charge
2. Greater ionic charge leads to stronger electrostatic attraction between oppositely charged ions
3. Mg²⁺ is smaller than Na⁺ (has a smaller ionic radius), so the interionic distance is shorter in MgCl₂
4. Smaller interionic distance (and higher charge) means greater charge density on Mg²⁺, resulting in a more exothermic lattice enthalpy for MgCl₂

## Key terms

- [lattice enthalpy](https://www.gradenine.co.uk/glossary/lattice-enthalpy)

## Related

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