Estimate Kapustinskii lattice energy in kJ/mol from charges and internuclear distance.
| U (kJ/mol) | – |
Use this calculator when you need a ballpark U for an MX salt without a full Born–Haber table.
The calculation is U ≈ 1.202×10⁵ × n × |z₊ z₋| × (1 − 0.345/r) / r, with r the cation–anion distance in ångströms. You type that distance in picometres (1 Å = 100 pm). n is ions per formula unit (2 for NaCl, 3 for CaF₂).
This is an order-of-magnitude Kapustinskii estimate, not a calorimetric lattice energy and not a full Born–Landé sum.
Ions per formula ν: Ions in the formula unit. 2 for NaCl, 3 for CaCl₂ or CaF₂.
z cation: Cation charge number. 1 for Na⁺, 2 for Ca²⁺.
z anion: Anion charge number. 1 for Cl⁻, 2 for O²⁻ (type 2).
r+ + r− (pm): Internuclear distance in picometres. Na–Cl is about 281 pm.
U (kJ/mol): Estimated lattice energy in kJ/mol, typically reported as a positive magnitude.
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