The nucleus of a hydrogen atom is a proton. The mass of a proton is 1.67 × 10–27 kg, whereas the mass of an incident α-particle is 6.64 × 10–27 kg. Because the incident α-particles are more massive than the target nuclei (protons), the α-particle won’t bounce back even in a head on collision. It is similar to a football colliding with a tennis ball at rest. Thus, there would be no appreciable scattering.