Lesson 3: 2.3 Structure of Ionic Solids
Duration of Days: 1
Lesson Objective
Explain the relationship between the structural features of an crystalline ionic solid and its physical properties.
How does Coulomb’s Law dictate the magnitude of the lattice energy holding an ionic crystal together?
Why do ionic crystals cleave and shatter smoothly when struck with a hammer instead of bending?
Lattice Energy
Crystalline Structure
Cleavage
Electrostatic Attraction
Ion Charge
Ionic Radius
Learning Objective 2.3.A; Suggested Skill 4.C (Model Analysis - Connect particulate scale to macroscopic properties).
Teaches the 3D alternating matrix of cations and anions. Students use Coulomb's Law to predict variations in lattice energy, melting point, and hardness. Crucial rule for AP: Ion charge always impacts lattice energy more dramatically than ion size.
Support: Provide a visual flowchart guiding students to check ion charges first when comparing melting points. If charges are identical, only then do they look at ionic radii.
Extension: Have students write a particulate-level narrative describing what happens to the layers of ions when an external shearing force is applied to a crystal of sodium chloride.
Two ionic compounds, NaF and MgO, crystallize in identical 3D geometries. The melting point of NaF is 993degrees C, while the melting point of MgO is 2,852 degrees C. Justify this massive difference in melting points using the principles of Coulombic attraction.