Final answer:
Repeating the alpha-particle scattering experiment with solid hydrogen instead of the gold foil would result in very little scattering due to hydrogen's much smaller nuclei. Most alpha particles would pass through, reaffirming the atom's mostly empty structure and the dense nature of even the lightest nuclei.
Step-by-step explanation:
If the alpha-particle scattering experiment were repeated using a thin sheet of solid hydrogen instead of gold foil, the expected results would differ significantly due to the vast difference in atomic mass between hydrogen and gold atoms. With hydrogen being the lightest element, it possesses a much smaller nucleus compared to the gold used in Rutherford's original experiment. Therefore, if alpha particles were directed at a thin sheet of solid hydrogen, the likelihood of them hitting a nucleus and being scattered back would be much lower than the 1 in 8000 occurrences observed with gold.
The alpha particles would mostly pass through the hydrogen foil with very little scattering, as hydrogen's single proton in the nucleus presents a much smaller target. The vast majority of the alpha particles would continue in their original direction, confirming that the atom is mostly empty space and that even the lightest nuclei are dense enough to cause noticeable effects only when directly hit by alpha particles.
If an alpha particle does directly hit the lone proton nucleus of a hydrogen atom, it would scatter, but the chances of this happening are much less than with the heavier gold nuclei. The Rutherford scattering would be observed to a lesser degree with hydrogen due to the reduced probability of direct hits on such small nuclei. Moreover, hydrogen's electrons would provide negligible scattering due to their minute mass relative to the mass of alpha particles.