before Rutherford explanation of atomic structure we know that atom is made up of solid positive sphere in which equal negative charge is randomly distributed
So here we can say if atom is like above then on incident of alpha particles they should deflect from the atom and no alpha particle must have to detect behind the atom on screen.
But here we can see in Rutherford experiment we have more than one spot where alpha particles hit the screen
So as per above result we can further say that positive part of nuclei is very small and it will deflect the alpha particle on if alpha particle pass near it.
So here we got more alpha particle behind the atom and then the new model of Rutherford is proposed for an atom