Explicit science instruction
An ionic solid is a repeating lattice of positive and negative ions. Strong electrostatic attractions extend throughout the structure, so separating ions generally requires substantial energy.
Solid ionic compounds often do not conduct electricity because ions are fixed in lattice positions. When melted or dissolved into mobile ions, charge can move through the material.
Brittleness can be explained by layer displacement: shifting like charges next to one another creates strong repulsion and can cleave the crystal.
Vocabulary: crystal lattice; lattice energy; conductivity; brittle; mobile ion.
Worked example with reasoning
A solid salt does not light a conductivity model, but its aqueous ion model does. The difference is not whether charged particles exist; it is whether those ions are mobile enough to carry current.
Guided question
Explain why a high melting point and lack of solid-state conductivity can both follow from the same lattice model.
Independent work
- Create a particle sketch for solid and molten ionic material.
- Use the sketch to explain conductivity in each state.
- Explain brittleness using a shifted-lattice diagram.
Misconception check
A substance can contain charged ions and still fail to conduct if those charges cannot move through the material.
Formative understanding check
Why can molten NaCl conduct while solid NaCl generally cannot?
Reveal response
Melting frees ions to move; in the solid lattice they are constrained to positions.
Public self-check only.
Mentor evidence conference
Ask Archaemenes to challenge your particle, charge, and evidence reasoning before you finalize the week record.
Teacher guidance
Foundation: Match three properties to lattice features.
Core: Build structure–property explanations for melting, conductivity, and brittleness.
Extended: Compare qualitative lattice attraction for ions with different charge and size while acknowledging the simplified model.
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