  A study is made of nuclear size corrections to the energy levels of
single-electron atoms for the ground state of hydrogen like atoms. We consider
Fermi charge distribution to the nucleus and calculate atomic energy level
shift due to the finite size of the nucleus in the perturbation theory context.
The exact relativistic correction based upon the available analytical
calculations is compared to the result of first-order relativistic perturbation
theory and the non-relativistic approximation. We find small discrepancies
between our perturbative results and those obtained from exact relativistic
calculation even for large nuclear charge number .
