The Net Total Particle Charge Surface Potential

different types of surface charge contribute to the net total particle charge on a colloid, denoted Gp. 

The unit of o is usually Coulomb nr2 (1 mol of charge units equals 1 Faraday or 96490 Coulombs). 

As we have seen, the electric state of a surface depends on the spatial distribution of free (electronic or ionic) charges in its neighborhood. The distribution is usually idealized as an electric double layer one layer is envisaged as a fixed charge or surface charge attached to the particle or solid surface while the other is distributed more or less diffusively in the liquid in contact (Gouy-Chapman diffuse model, Fig. 3.2). A balance between electrostatic and thermal forces is attained. 

According to the Gouy-Chapman theory the surface charge density gp [C nr2] is related to the potential at the surface y [volt] (Eq. (vi) in Fig. 3.2) 

The surface complexation approach is distinct from the Stern model in the primacy given the specific chemical interaction at the surface over electrostatic effects, and the assignment of the surface reaction to the sorption reactions themselves (Dzombak and Morel, 1990). 

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