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Ionic Lattice Energies

APCHEM-EMDLBI

Given the following ion sketches:

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The lattice energy of an ionic, crystalline solid is the result of the Coulombic forces among the ions that make up that crystal.

Consider Choices 'A' through 'D' below.

Which of the following CORRECTLY identifies the combination that would have the greatest ionic lattice energy and provides a valid explanation for why that combination has the strongest interionic forces?

A

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The total charges are +2 and [$2\times (-1)$]. Since ${ Mg }^{ 2+ }$ is the smallest cation, and chloride is only slightly larger than sulfide, this combination involves the strongest Coulombic attraction.

B

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While sulfide ion, ${ S }^{ 2– }$, is slightly larger than chloride ion, ${Cl}^{–}$, the greater charge magnitude results in a stronger Coulombic force.

C

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The magnitude of the Coulombic force varies inversely with the square of the distance between the centers of charge. Since ${Na}^{+}$ and ${Cl}^{–}$ are the smallest ions, this combination will have the greatest Coulombic force.

D

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Total charges are [$2\times (+1)$] and -2, and ions involved are small, so the distance between the centers is smaller. Coulombic force increases with decreasing distance between the centers of charge.