By Drew Lichtenstein – Updated Mar 24, 2022

Lattice energy quantifies the strength of an ionic bond—the electrostatic attraction that holds ions together in a solid. A classic example is table salt (NaCl). The Born–Landé equation allows chemists to calculate this energy from readily available crystal parameters.

Step 1: Insert the universal constants

The Born–Landé expression contains several fixed constants that never change:

• Avogadro’s number, NA = 6.022 141 79 (30) × 10²³ mol⁻¹
• Elementary charge, e = 1.602 176 487 (40) × 10⁻¹⁹ C
• Permittivity of free space, ε₀ = 8.854 × 10⁻¹² C² J⁻¹ mol⁻¹

Step 2: Plug in the compound‑specific variables

For each salt, the following parameters differ:

• Madelung constant, M (dimensionless; varies with crystal structure)
• Cation charge, Z⁺
• Anion charge, Z⁻
• Nearest‑neighbour distance, r₀ (in meters)
• Born exponent, n (typical range 5–12)

Step 3: Evaluate the Born–Landé equation

The lattice energy (E) is calculated as:

E = -\frac{N_A M Z^+ Z^-}{4\pi \epsilon_0 r_0}\,[1-\frac{1}{n}]

Compute the expression inside the brackets first, then multiply by the prefactor. The resulting value is expressed in kilojoules per mole (kJ mol⁻¹) and will always be negative, reflecting the exothermic nature of lattice formation.

Important Note

Do not drop the leading negative sign—omitting it will give a positive value, which is physically incorrect.

For deeper insight, consult the original Born–Landé derivation or recent crystallography texts.