Chemical reactivity descriptors are computed by the use of three alternative approaches derived within the framework of density functional theory. These schemes consider the computation of orbital Fukui indices,. where all valence orbitals are taken into account; the Fukui indices of each atom in the molecule from the atomic resolved hardness matrix; and the atom in molecule softnesses, expressed in mixed LCAO representation of second quantization as functions of Mayer atomic valences. The hardness matrix is constructed from the Kohn-Sham orbitals by the use of the fractional occupation number concept and Janak's extension of density functional theory. The site reactivity of molecules involved in radical attack reactions of some substituted olefins and isocyanide addition to dipolarophiles is rationalized in terms of the orbital and atomic resolved reactivity indices. The reactivity descriptors of thiophene, furane, and pyrrole are also reported and discussed. In addition, the nucleophilic attack on the allyl coordinated to the electronically asymmetric [Pd(phosphine)(imine)] fragment was considered.