CHM 501

34. Calculate the lattice energy for Al2O3. Estimate the Born exponent based on the electron configurations of the ions.

Answer

The quantities needed to be estimated to use the Born-Landé equation are the Madelung constant, the Born exponent, and the internuclear distance between the Al3+ and the O2– ions.

The Madelung constant is found from Table 5.12 (DMA) to be 4.040.

The Born exponent is found from electron configurations: Al3+ and O2– both have the [Ne] electron configuration so n = 7.

The internuclear distance is the sum of the cationic (DMA Table 5.8, CN = 6) and anionic radii (DMA Table 5.10) = 67.5 + 126 = 193.5 pm.

Using these values:

Elat = 14910 kJ/mol