The value of its lattice energy is -787 kJ/mol. Lattice energy, E lattice is dependent on the strength of the bond between the cation and anion in an ionic bond. A high negative value of lattice energy indicates that the formation of NaCl is highly favored.
The stronger the bond, the higher the lattice energy. Recall, lattice energy is positive meaning it is endothermic. Coulomb’s law is equal to a constant, k, multiplied by the product of the ion charges, z 1 and z 22, between the ions. Lattice Energies and the Strength of the Ionic Bond. Lattice energies are large when ions are closer together, the distance between the ions is small and when the charges are larger. The strength of the bond between the ions of opposite charge in an ionic compound. For example, the lattice energy of NaCl is larger than the lattice energy of KCl. This is because the charges are the same, but the potassium ion is larger than the sodium ion. The Born-Haber cycle may also be used to calculate any one of the other quantities in the equation for lattice energy, provided that the remainder is known. In the case of NaCl and MgCl 2, the MgCl 2 has the larger lattice energy because the magnesium cation is smaller, and the charge is a +2 rather than a +1 for the sodium ion.īelow is a table with the lattice energies of some ionic compounds. A more extensive list can be found in other tables or in the Handbook of Physics and Chemistry.Įxercise 1. Consider the following Born-Haber cycle for MgF 2. What is the lattice energy for MgF 2?Įxercise 2. Order the following ionic compounds from lowest to highest lattice energy. Which has the highest lattice energy, Na 3P or Na 2S?Įxercise 4. The sublimation energy for Sr is 164 kJ/mol, E i1 = +549.5 kJ/mol, E i2 = +1064.2 kJ/mol, E ea for Cl (g) = -348.6 kJ/mol, energy for the formation of one mole of SrCl 2 from its elements = -803.7 kJ/mol, and the bond dissociation energy for Cl 2 (g) = +243 kJ/mol.Įxercise 5.
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