Debye-Huckel theory extended form

Normally, the validity of the Debye—HUckel theory extends little further than kR <1. At room temperature, this requires ionic concentrations < 0.1 mol dm for univalent ions in water, 0.03 mol dm for univalent ions in ethanol or <0.01 moldm for univalent ion in ethers. In these cases, ions may be regarded as point particles and the strong repulsive core potential ignored. Furthermore, the time taken for non-reactive ions to diffuse far enough to establish an ionic-atmosphere around an ion, which was suddenly formed in solution containing only univalent ions, is... 

The Debye-Huckel Theory The Finite-Ion-Size Model. If the approximation of the point charge is removed, the extended form of the Debye-Huckel law is obtained ... 

We shall just mention here that the simple association theory may be extended by considering the interactions between defects in solution in a medium with dielectric constant a [14]. This is analogous to the Debye-Huckel theory of electrolytic solutions. As a result, the mole fractions of charged point defects of sort i in the mass action laws have to be replaced by their corresponding activities which according to Debye-Huckel are of the form... 

It is possible to understand why solutions of electrolytes do not behave in an ideal manner in terms of both the coulombic attraction on ions which serves to constrain their movement and the thermal agitation which counteracts this restraint. Debye and Huckel developed a theory in which electrostatic forces shaping the behavior of the ions in solution as well as their finite radii formed a basis from which expressions for the activity coefficient of an ion could be derived. One of the simpler usable equations they developed, referred to as the Extended Limiting Law, gives the activity coefficient, y, of an ion i, having a charge Zj in a solution of ionic strength I. 

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