Ernest Rutherford in 1909 conducted what is now a famous experiment where he bombarded gold foil with alpha particles (Helium nuclei). A source which undergoes for alpha decay is placed in a lead box with a small window in it. Any of the alpha particles which hit the inside of the box are simply stopped by the box. Only those particles which pass through the opening are allowed to escape, and they follow a straight line along with gold foil.

Observations

Most of the alpha particles pass straight through the gold foil.

1. Some of the alpha particles get deflected by very small amounts.
2. A very few get deflected greatly.
3. Even fewer get bounced of the foil & back to the left.

Conclusions

1. The atom having 99.99% empty space.
2. The nucleus contains a positive charge & most of the mass of the atom.
3. The nucleus is near about 100,000 times smaller than the atom.

                                                             Rutherford's Experiment