Let us consider an atomic orbital, for example n=2, l=1, m=0 in Hydrogen. The probability plot is given in the figure attached. This picture can be obtained experimentally: via X-ray and elastic electron scattering. Each negative sub-cloud carries a fractional charge. Fortunately, we have quantum mechanics to explain it but if the scattering experiments had been carried out before QM establishing, would we have advanced a parton-like hypothesis for atoms? I do not know if it would be correct to consider each sub-cloud as an "elementary" particle with a fractional charge. Do you? . .