Electron-pair intracule (relative motion) (h) over bar(upsilon) and extracule (center-of-mass motion) (d) over bar(P) densities in momentum space are studied for the P-3, D-1, and S-1 terms of five group 14 atoms with p(2) configurations, the S-4, D-2, and P-2 terms of five group 15 atoms with p(3) configurations, and the P-3, D-1, and S-1 terms of five group 16 atoms with p(4) configurations. Common to all fifteen atoms, the intracule densities show that a low energy term has a greater probability of finding a pair of electrons with a large relative momentum upsilon than a high energy term. The Fermi hole effect in a high spin term appears naively in momentum space, and the average relative momentum [upsilon] is larger in a high angular momentum term. For the terms arising from the p(m) electronic configurations (m = 2-4), the differences in the radial extracule densities are found to be almost isomorphic with the corresponding intracule ones. In a term with a high angular momentum, the average center-of-mass momentum [P] of an electron pair is always larger, and two electrons are less likely to have opposite momenta. The major origin of these differences in the electron-pair densities lies in the valence np orbitals, and the contribution of different electron-pair motions to the relative stability of terms can be explained by a rigorous relation between the kinetic energy T-np and the second intracule [upsilon(2)](np) and extracule [P-2](np) moments of the valence np subshell.