We report here, for the first time, large and systematic chemical effects on the "atomic" X-ray absorption fine structure (AXAFS) for a series of Pt-Ru alloys as a function of the composition and for an in situ Pt electrode as the electrode potential is increased. These changes are seen in the Fourier transform of the normal chi(E) function in XAFS, where the AXAFS produces a peak at the characteristic atomic radius. Curved-wave multiple-scattering cluster calculations (FEFF6) confirm the changes with alloy composition and electrode potential, although the theory overestimates the size of the changes. Obvious reasons for this are given. The systematic chemical effects and agreement with theoretical predictions provide strong support for their interpretation as AXAFS features, rather than multielectronic excitations. The AXAFS structure and its interpretation offers the promise of providing a new tool for observing in situ electronic (AXAFS) and geometric (normal EXAFS) structural changes simultaneously in complex systems where long range order is not required.