Lattice energy estimates from an electrostatic model

13 Lattice energy estimates from an electrostatic model 

The lattice energy, A 1/(0 K), of an ionic compound is the change in internal energy that accompanies the formation of one mole of the solid from its constituent gas-phase ions at OK. 

For a salt MX , equation 5.7 defines the reaction, the energy change for which corresponds to the lattice energy. 

The lattice energy can be estimated by assuming an electrostatic model for the solid state ionic lattice the ions are considered to be point charges. Later in this chapter, we consider to what extent this approximation is true. 

Before we consider an ionic lattice, let us review the appropriate equation for the change in internal energy when two oppositely charged ions M and X are brought together from infinite separation to form the isolated ion-pair, MX (equation 5.8). 

The structures of some high-temperature superconductors are also related to that of perovskite. Another mixed oxide lattice is that of spinel, MgAl204 (see Box 13.6). 

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Chapter 5 Lattice energy estimates from an electrostatic model 153... 

The high-temperature form of KBF4 crystallizes with a CsCl structure and we can estimate the lattice energy using an electrostatic model, assuming that the [BF4] ion can be treated as a sphere (see Figure 6.17). The lattice energy of KF is known, and can be determined from the... 

The crystal lattice energy can be estimated from a simple electrostatic model When this model is applied to an ionic crystal only the electrostatic charges and the shortest anion-cation intermiclear distance need be considered. The summation of all the geometrical interactions be/Kveeti the ions is called the Madelung constant. From this model an equatitWjor the crystal lattice energy is derived ... 

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