Volume 3 of the 5-volume Quantum Nanochemistry presents the chemical reactivity throughout the molecular structure in general and chemical bonding in particular by introducing the bondons as the quantum bosonic particles of the chemical field, localization, from Hückel to Density Functional expositions, especially in relation to how chemical principles of electronegativity and chemical hardness decide the global chemical reactivity and interaction. The volume presents the fundamental and advanced concepts, principles, and models as well as their first and novel combinations and applications in quantum (physical) chemical theory of bonding, molecular reactivity, and aromaticity.