Step 1: Summarise the observations. When alpha particles struck the thin gold foil, three things were seen: the great majority went through with little or no deflection, some turned through appreciable angles, and a rare few rebounded backwards.
Step 2: Draw conclusions from each observation. The undeflected majority tells us the atom is mostly hollow. A deflection needs a repulsive push, and a near-backward rebound needs an extremely intense push acting over a tiny region, meaning the positive charge and mass are not spread out but concentrated.
Step 3: The conclusion (nuclear model). Rutherford therefore proposed that each atom possesses a minute central nucleus that holds the whole positive charge and almost the entire mass, while the light electrons occupy the surrounding empty volume. This overturned the earlier uniform-sphere (plum-pudding) picture.
\[\boxed{\text{Result: a small, heavy, positively charged nucleus exists at the atom's centre.}}\]