Ionic bonding and lattice energy
In an ionic bond, one atom hands electrons to another, making positive and negative ions that attract. The ions pack into a crystal lattice. Lattice energy is the energy released when gaseous ions form one mole of the solid.
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Analogy
Like magnets snapping into a stable stack: bigger charges and closer centres give a firmer grip.
Example
Coulomb: energy ∝ (q₁ × q₂) / distanceNaCl: (+1)(−1) = 1MgO: (+2)(−2) = 4MgO is much larger.
In practice
MgO melts above 2800 °C, far higher than NaCl at about 801 °C, because Mg²⁺ and O²⁻ have double the charges.
Practice
Flashcards
- What does lattice energy depend on?The ion charges (higher is stronger) and the ion sizes (smaller is stronger).
Questions people ask
Why do ionic solids have high melting points?
Each ion is held by strong attractions to many neighbours in all directions. To melt the solid, you must give enough energy to pull the ions out of their fixed positions. That takes a lot of heat, so ionic compounds melt at high temperatures.
Why do ionic compounds conduct electricity only when molten or dissolved?
In the solid, ions are locked in the lattice and cannot move. When the compound melts or dissolves, the ions are free to travel. Moving charged particles carry current, so the liquid or solution conducts while the solid does not.