Chemical reactions take place due to the redistribution of electron density among the reacting partners. Focusing on changes in electron density, which accompany the breaking and forming of chemical bonds, instead of the changes in the wave function accompanying them, allows us to use the ‘‘classical’’ three-dimensional language. Conceptual density functional theory (DFT) quantifies the possible responses of the system to various changes in density. Popular concepts like electronegativity, hardness, and electrophilicity, which explain a large number of diverse types of reactions in a systematic fashion, are grounded in conceptual DFT
