Debye–Hückel theory

Summary

Debye–Hückel theory describes dilute solutions of ions, such as salt dissolved in water. It combines Poisson's equation in electrostatics with the Boltzmann distribution of the ions and linearizes the result. Its main prediction is screening: the potential of an ion decays like $e^{-r/\lambda_D}/r$, where $\lambda_D$ is the Debye length. It also gives the activity coefficient of the ions in very dilute solutions. Its logarithm decreases like the square root of the ionic strength.