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Structure of Ionic Solids

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An ionic compound is a 3-D lattice of alternating cations and anions, not a collection of separate molecules. Each ion is surrounded by many oppositely charged neighbors, and the Coulombic attraction pulls in every direction at once. That network of strong attractions makes ionic solids hard, brittle, and high-melting.

UNIT 2 TOPIC 2.3 • STRUCTURE OF IONIC SOLIDS LATTICE BUILDER AP Chemistry · Unit 2 · Compound Structure & Properties An ionic solid is a 3-D lattice of alternating cations and anions held by strong electrostatic (Coulombic) attractions. IONIC LATTICE · INTACT + − + − + − + − + − + − + − + − + − + − + − + − + Na+ sodium ion · cation Cl− chloride ion · anion (larger) 1 : 1 ratio of Na+ to Cl− throughout + STRONG COULOMBIC ATTRACTION IN ALL DIRECTIONS Each ion is surrounded by many oppositely-charged ions — attractions act in every direction, giving a stable 3-D crystal. LAYERS SHIFT → BRITTLE FRACTURE + − + − + − + − + − + − + − + − + − + − SHEAR like charges align → REPEL BRITTLE FRACTURE Shifting one layer lines up ions of the same charge across the slip plane. The sudden repulsion splits the crystal — ionic solids are hard but brittle (they shatter rather than bend). PROPERTIES OF IONIC SOLIDS CRYSTALLINE regular repeating 3-D lattice pattern HIGH MELTING PT. strong attractions need much energy HARD BUT BRITTLE shift aligns like charges → fracture CONDUCTS WHEN molten or dissolved (mobile ions; not as solid) CED ANCHOR 2.3.A Ionic solids are 3-D lattices of alternating ions held by Coulombic attraction. This structure explains their high melting points, hardness, brittleness (a shifted layer aligns like charges), and electrical conduction only when molten or dissolved.
An ionic solid is a 3-D lattice, not a cluster of molecules. Every ion is surrounded by oppositely charged neighbors, and the strong Coulombic attraction acts in all directions at once, giving a rigid, high-melting crystal.
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The mistakes here treat a lattice like a molecule: reading a formula unit (NaCl) as a discrete molecule, expecting strong bonds to make the solid malleable, and imagining melting as breaking atoms apart. Melting an ionic solid separates ions from the lattice; it does not atomize anything, and the rigidity comes from the very strength of the attractions.

The work

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Lesson
Ionic Solids ›

Ionic solids are lattices held by Coulombic attraction in all directions, which is why they are brittle and high-melting. The lesson builds the lattice and reads its properties, then closes with a ten-scenario check.

Skill check · 10 scenarios
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Diagnostic
10-item topic check ›

Ten items spanning the three Topic 2.3 misconceptions: a formula unit read as a molecule, strong bonds assumed to make a solid malleable, and melting misread as atomizing the ions.

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Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

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