Rutherford took a very thin gold foil and bombared it with alfa - particles. He observed that:
(i) Most of the fast moving a - particles passed straight through the gold foil.
(ii) Some of the alpha particles were deflected by the foil by small angle.
(iii) Out of every 12000 particles, one appeared to rebound.
From the above observations be concluded:
(i) There is a positively charged centre in an atom called the nucleus. Nearly all mass of an atom resides in the nucleus.
(ii) The electrons revolve around the nucleus in well defined orbits.
(iii) The size of the nucleus is very small as compared with the size of the atom.