Explicit science instruction
Ions form when electron count differs from proton count. Losing electrons produces a positive ion; gaining electrons produces a negative ion. The nucleus does not change during ordinary ion formation.
Ionic bonding is modeled as electrostatic attraction among oppositely charged ions. A crystal contains a repeating three-dimensional arrangement rather than isolated molecule pairs.
Charge and stoichiometry are linked: a stable empirical formula must represent overall electrical neutrality.
Vocabulary: ion; cation; anion; valence electron; electrostatic attraction.
Worked example with reasoning
Magnesium commonly forms Mg²⁺ and chlorine forms Cl⁻. Two chloride ions are required for each magnesium ion, giving MgCl₂ and net charge +2 + 2(−1)=0.
Guided question
Use electron-count reasoning to explain why Na⁺ and O²⁻ combine in a 2:1 ratio.
Independent work
- Write ion symbols for Li, Mg, Al, O, and Cl in a simple main-group model.
- For three cation–anion pairs, calculate the smallest whole-number charge balance.
- Explain why the formula ratio describes electrical neutrality rather than a molecule count.
Misconception check
Ionic bonding is not simply one atom handing an electron to one partner and then becoming a permanently isolated pair; the solid is a many-ion electrostatic lattice.
Formative understanding check
Why is MgCl rather than MgCl₂ inconsistent with Mg²⁺ and Cl⁻ charges?
Reveal response
MgCl would have net +1 charge; two Cl⁻ ions are needed to balance one Mg²⁺.
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: Use a charge-balance table.
Core: Derive formulas from common ion charges and explain lattice attraction.
Extended: Compare charge magnitude with qualitative lattice attraction while identifying model limits.
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