All electron nonrelativistic and relativistic density functional theory calculations at the BP86/QZ4P (Slater type) level are reported for a set of fundamentally useful DFT based reactivity descriptors for group 14 elements (C, Si, Ge, Sn, Pb, Element 114 (abbreviated as Uuq)) and functional groups, -XY3 (X = C, Si, Ge, Sn, Pb, Element 114 (Uuq); Y = CH3, H, F, Cl, Br, I, At); these include electronegativity (chi), chemical hardness (eta), global softness (S), and electrophilicity index (omega). This approach permits an evaluation of the discrepancies in electronegativity scales and associated properties at uniform levels affording a nonempirical analysis for the first time. The vital importance of the spin-orbit interaction, in addition to the scalar relativistic terms, is demonstrated in reproducing the experimental trends on going from top to bottom of the group. The order for isolated atoms is altered when passing to -XY3 groups for all of the properties studied. For example, the calculated atomic electronegativities show a uniform decrease from C to Pb increasing again to Uuq as verified in the experimental data for C-Pb but at variance with several other scales. The sequence for functional groups is different and in accordance with experimental NMR data where available. The experimental hardness sequence for the isolated atoms (C > Pb > Si > Ge > Sn) is opposed to the trends of decreasing hardness on going down the periodic table as is found, e.g., in the halogen group and confirmed by this study. The -XY3 functional groups however follow the C > Si > Ge > Sn > Pb sequence. The recently developed electrophilicity index (w) has been shown to be highly correlated with the electron affinity rather than the electronegativity. Finally, regression analyses that discriminate between the properties are carried out to investigate the nature of additivity of atomic contributions in functional group properties.