🧱 Step 1: The Ionic Crystal Lattice

Before dissolution can occur, you need to understand what you are starting with. An ionic compound like NaCl exists as a crystal lattice — a highly ordered, three-dimensional arrangement of alternating positive and negative ions held together by strong electrostatic attraction (ionic bonds).

In NaCl, every Na⁺ ion is surrounded by six Cl⁻ ions, and every Cl⁻ is surrounded by six Na⁺. These attractions are very strong, which is why ionic compounds have high melting points (NaCl melts at 801°C) and are solid at room temperature.

For dissolution to occur, these strong ionic bonds must be broken. This requires energy. The energy needed to completely separate all the ions in a crystal lattice is called the lattice energy. Breaking the lattice is an endothermic process (ΔH > 0, energy absorbed).