  We investigate charged particles circular motion in the gravitational field
of a charged mass distribution described by the Reissner-Nordstr\"om spacetime.
We introduce a set of independent parameters completely characterizing the
different spatial regions in which circular motion is allowed. We provide most
complete classification of circular orbits for different sets of particle and
source charge-to-mass ratios. We study both black holes and naked singularities
and show that the behavior of charged particles depend drastically on the type
of source. Our analysis shows in an alternative manner that the behavior of
circular orbits can in principle be used to distinguish between black holes and
naked singularities. From this analysis, special limiting values for the
dimensionless charge of black hole and naked singularity emerge, namely,
Q/M=1/2, $Q/M=\sqrt{13}/5$ and $Q/M=\sqrt{2/3}$ for the black hole case and
Q/M=1, $Q/M=5/ (2 \sqrt{6})$, $Q/M=3 \sqrt{6}/7$, and finally $Q/M= \sqrt{9/8}$
for the naked singularity case. Similarly and surprisingly, analogue limits
emerge for the orbiting particles charge-to-mass ratio $\epsilon$, for positive
charges $\epsilon=1$, $\epsilon=2$ and $\epsilon=M/Q$. These limits play an
important role in the study of the coupled electromagnetic and gravitational
interactions, and the investigation of the role of the charge in the
gravitational collapse of compact objects.
