in gold foil expriment,99% of alfa …

Rutherford  postulated  that  the  atom  must  contain  large  empty  spaces  as  most  of  the  α-particles passed through it without getting deflected. Some α-particles were deflected by the foil through small angles, while some were deflected through very large angles. Thus, Rutherford concluded that the positively charged particles in an atom must be concentrated in a very small space.

One  out  of  every  12,000  particles  were  deflected  through  180o showing  a  full  rebound. Thus, Rutherford came to the conclusion that all the positive charges of the atom and most of the mass of the atom is concentrated in a very small volume within the atom.

Rutherford  named  this  small  space  inside  the  atom  as  the nucleus  of  the  atom or  the atomic nucleus. On the basis of these observations, Rutherford calculated that the atomic nucleus is 10⁵ times smaller than the total area of the atom. The radius of the atom is 10^-8 centimetres while the radius of the nucleus is 10^-13 centimetres.

Thus, we can say that the atom is relatively hollow with a heavy nucleus at its centre.  The electrons arranged around the nucleus possess negligible mass.