Even though we cannot see them directly we do believe so. There is now a large amount of indirect data that is consistent with the existence of atoms. A hundred years ago most scientists just started to agree.
Experiments show that electrons come out of atoms.
Need new model. Gives wrong predictions for absorption frequencies and alpha scattering. P particles per square centimeter per second. They need to get closer to the nucleus than the corresponding value of b. where and are related by the scattering formula above. If the angle theta is large, the value of b is very small.