01The potential energy curve
As two atoms approach, energy drops as attraction grows, then rises sharply when nuclei repel. The minimum is the bond length; its depth is the bond energy.
Triple bonds are shorter and stronger than double, which beat single bonds. For ions, Coulomb's law: larger charges and smaller ions → stronger lattice energy.
02Notebook box
Bond order ↑ → length ↓, energy ↑. Lattice energy ∝ (q₁q₂)/r.
Worked example: Higher melting point, NaCl or MgO? → MgO (+2/−2 charges, smaller ions).