Ernest Rutherford's experimental results greatly surprised him. What do you think Rutherford had been expecting to find? Imagine that you lived in...

Rutherford discovered the proton, and he also discovered that the atom is mainly empty space.

He noticed that a beam of alpha particles was scattered back where it came from by gold atoms, and, since it was known that alpha particles were positive, it was deduced that there was a dense positive core in the nucleus. This dense positive core was called the protons.

Rutherford deduced that the electrons were arranged in concentric shells around...

Rutherford discovered the proton, and he also discovered that the atom is mainly empty space.

He noticed that a beam of alpha particles was scattered back where it came from by gold atoms, and, since it was known that alpha particles were positive, it was deduced that there was a dense positive core in the nucleus. This dense positive core was called the protons.

Rutherford deduced that the electrons were arranged in concentric shells around this positive core, and this was in stark contrast to the model of the atom that was previously put forth by J.J. Thompson - the plum pudding model - which held that the electrons were scattered in a blob of positive charges like plums in a pudding. Rutherford expected to find the J.J. Thompson model with positive and negative particles - electrons and protons - all mixed together. 

A solar system model in which the electrons were arranged in concentric shells would cause wide angle scattering of x-rays whereas a plum pudding model would not because the positive charge would be more diffuse and allow the alpha particles to pass through. Clearly, anyone who was contemporary with Rutherford would have been (and was) surprised by his model altering discovery.