The effects that a polarizable medium exerts on the electronic chemical potential and the chemical hardness of neutral and charged molecules are discussed in detail, using the continuum approach based on the polarizable charge model. The variations in electronic chemical potential result from charge transfer between the solute and the solvent, a result which is confirmed by supermolecule calculations. Both models predict that chemical hardness diminishes in solution phase due to the decrease in electrostatic potential that result from the increase of the effective radii of neutral and charged solutes. (c) 2006 Elsevier B.V. All rights reserved.