We investigate the motion of neutral test particles in the gravitational
field of a mass M with charge Q described by the Reissner-Nordstr\"om (RN)
spacetime. We focus on the study of circular stable and unstable orbits around
configurations describing either black holes or naked singularities. We show
that at the classical radius, defined as Q2/M, there exist orbits with zero
angular momentum due to the presence of repulsive gravity. The analysis of the
stability of circular orbits indicates that black holes are characterized by a
continuous region of stability. In the case of naked singularities, the region
of stability can split into two non-connected regions inside which test
particles move along stable circular orbits.Comment: 23 pages, 22 figures. To be published Phys. Rev.
