Structure of Ionic Solids

AP Chemistry· difficulty 3/5

The bar chart compares lattice energies of four ionic compounds. Lattice energy magnitude depends on ion charges and the distance between them.

Lattice Energy (kJ/mol) NaCl NaBr MgO Al2O3 787 747 3795 15916

Why does Al2O3 have the largest lattice energy?

  • A

    Al has lower ionization energy than Na

  • B

    Smaller atoms automatically yield higher lattice energies

  • C

    Larger ionic charges (3+ and 2-) increase the electrostatic attraction

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  • D

    It contains more atoms per formula unit

Explanation

Lattice energy is proportional to (q1·q2)/r; the larger product of charges in Al2O3 dominates and makes its lattice energy by far the largest.

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