Lattice Energy Calculator
The lattice energy of an ionic compound — the energy holding the crystal together — by the Born-Landé equation.
Lattice energy is the energy released when gaseous ions come together into a crystal.
How the lattice energy calculator works
Lattice energy is the energy released when gaseous ions come together into a crystal. The Born-Landé equation combines the electrostatic attraction with a repulsive term: U = −N_A M z⁺z⁻ e² (1 − 1/n) / (4πε₀ r₀).
The charges dominate. Magnesium oxide, with 2+ and 2− ions, has a lattice energy near 3,800 kJ/mol against sodium chloride's 787 — which is why it melts at 2,852 °C rather than 801.
Formula: U = −N_A M z⁺z⁻ e² (1 − 1/n) / (4πε₀ r₀)
Worked examples
| Inputs | Lattice energy | Note |
|---|---|---|
| Sodium chloride | 753.4 kJ/mol | about 755 kJ/mol against a measured 787 |
| Magnesium oxide | 3,964 kJ/mol | about 3,900 kJ/mol |
| Caesium chloride | 622.4 kJ/mol | lower — larger ions |
FAQFrequently asked questions
What is lattice energy?
The energy released when gaseous ions come together to form one mole of an ionic crystal. It is a measure of how tightly the lattice is bound.
Why is magnesium oxide so much stronger than sodium chloride?
Charges. MgO has 2+ and 2− ions against NaCl's 1+ and 1−, so the electrostatic term is four times larger — and the ions are smaller.
What is the Madelung constant?
A geometric factor accounting for all the ions in the lattice, not just the nearest neighbour. It depends only on the crystal structure.
What is the Born exponent?
It describes how sharply ions repel at short range, typically 5 to 12. Larger, more polarisable ions have higher values.
How accurate is Born-Landé?
Usually within a few per cent for genuinely ionic compounds. It gets worse as covalent character increases — silver halides deviate substantially.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- CSIRO — Australia's national science agency
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.