  The structural, magnetic and electronic properties of transition metal oxides
reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray
scattering (RXS) allows us to perform an accurate investigation of all these
electronic degrees. RXS combines high-Q resolution x-ray diffraction with the
properties of the resonance providing information similar to that obtained by
atomic spectroscopy (element selectivity and a large enhancement of scattering
amplitude for this particular element and sensitivity to the symmetry of the
electronic levels through the multipole electric transitions). Since electronic
states are coupled to the local symmetry, RXS reveals the occurrence of
symmetry breaking effects such as lattice distortions, onset of electronic
orbital ordering or ordering of electronic charge distributions. We shall
discuss the strength of RXS at the K absorption edge of 3d transition-metal
oxides by describing various applications in the observation of local
anisotropy and charge disproportionation. Examples of these resonant effects
are (I) charge ordering transitions in manganites, Fe3O4 and ferrites and (II)
forbidden reflections and anisotropy in Mn3+ perovskites, spinel ferrites and
cobalt oxides. In all the studied cases, the electronic (charge and/or
anisotropy) orderings are determined by the structural distortions.
