Chemical concepts including global and orbital (or "divisional") electronegativity, hardness, softness, orbital hardness and softness kernel, and orbital Fukui index, for any given electronic system in a particular situation, are defined and relations among them are derived. Some results earlier obtained are used to illustrate uses df the formalism. Atomic parameters in various molecular circumstances are determined through semiempirical calculations as functions of corresponding atomic orbital population distributions. It is demonstrated bow atomic energy changes such as ionization energy and electron affinity and transition energy can be calculated. Computed values agree well with experiment, The density-functional and L. C. Allen views of the electronegativity concept are reconciled.