Understanding how nuclear stability varies along isotopic chains is an important part of nuclear-structure studies. In this work, the semi-empirical mass formula (SEMF) is used to calculate nuclear binding energies for selected radium (Z = 88) and uranium (Z = 92) isotopes. One-neutron separation energies (Sₙ), two-neutron separation energies (S2n), and alpha-decay Q-values (Qα) are derived from the calculated binding energies and compared with evaluated experimental data from the AME2020 atomic mass evaluation. The analysis covers ²¹⁰–²³³Ra and ²¹⁸–²⁴⁰U, corresponding to neutron numbers N = 122–145 for Ra and N = 126–148 for U. The SEMF reproduces the smooth binding-energy systematics reasonably well, but it does not reproduce the localized shell structure visible in separation energies. For Ra, the mean absolute errors are about 0.38 MeV for Sₙ, 0.76 MeV for S₂ₙ, and 1.60 MeV for Qα; for U, the corresponding values are about 0.20, 0.29, and 0.85 MeV when AME2020 estimated entries are excluded from the error statistics. The N = 126 region provides a clear illustration of the limitation: the experimental two-neutron shell-gap indicator is substantially larger than the smooth SEMF prediction. The study also shows that the alpha-decay energy is sensitive to the balance between binding changes in the parent and daughter nuclei and to the increasing Coulomb contribution with atomic number. The originally proposed interpretation of an inverse separation-energy/Qα relationship is therefore treated carefully: the chain-wise Pearson correlations are positive because both quantities have a strong dependence on mass number, whereas correlations of successive changes show a strong local anti-correlation for S₂ₙ and Qα (approximately r = −0.93 for Ra and −0.96 for U). The results confirm that SEMF is useful for broad trends in heavy nuclei but requires shell and deformation corrections for quantitative description of localized structure.................. Keywords:................. Semi-empirical mass formula, nuclear binding energy, separation energy, alpha-decay Q-value, radium isotopes, uranium isotopes.