Question on a textbook statment on Rutherford Scattering

[User1265]

Homework Statement

There is a Physics textbook that states,
"Rutherford reasoned that:

"The core of the atom must be massive on atomic scale to deflect alpha particles through large angles."

Relevant Equations

F=kQ1Q2/R^2

The experimental observation of finding very few alpha particles scattered through large angles (>90) - I thought this would have inferred that the positive charge of the core of the atom (which we now come to know as the nuclei) must have been great in order greatly deflect alpha particles that came in its vicinity.
I came to this conclusion as I thought,
For a nuclei with smaller electric charge, it would result in the same alpha having a smaller angle of deflection , compared to that of a larger nulcei.

I don't understand how the size of the nulceus could effect how alpha particles are sctattered, and how the statement above is true .

 

[hutchphd]

Have you ever played pool (pocket billiards)? Can you get the cue ball to bounce backwards (no "English" allowed)?

 

[kuruman]

You have to understand how the atom was modeled before the Rutherford experiment. Electrons were already known to be part of the atom. They also knew that atoms are electrically neutral. So the total negative charge of the electrons must be equal to the total charge of whatever else makes the atom. The plum pudding model was proposed in which the atom was a mass of positively charged pudding with electrons as the "raisins" in this Brit delicacy. Rutherford reasoned that if one is to verify this model, one ought to stick a finger (in this case positive alpha particles) and see what happens. Unexpectedly the finger sometimes bounced back at large angles which would be more consistent with a hard positively charged walnut at the center of the raisin distribution containing almost all the mass of the atom.