  We investigate the isospin-violating mixing of the light scalar mesons
a0(980) and f0(980) within the unitarized chiral approach. Isospin-violating
effects are considered to leading order in the quark mass difference and
electromagnetism. In this approach both resonances are generated through
meson-meson dynamics. Our results provide a description of the mixing
phenomenon within a framework consistent with chiral symmetry and unitarity,
where these resonances are not predominantly quark-antiquark states. We discuss
in detail the reactions J/Psi to phi S, where S denotes a suitable pair of
pseudo--scalar mesons in the scalar channel, namely pi0 eta, K+K-, and K0 \bar
K^0. In this work predictions for the cross section in the kaon channels are
given for the first time with isospin violating effects included.
