Most of the α-particles passed through the gold foil undeflected.
A small fraction of the α-particles was deflected by small angles.
A very few α-particles (< 1 in 20,000) bounced back, that is, were deflected by nearly 180°.
As majority of the α-particles went through the foil undeflected, this indicates most of the space in an atom is empty.
The scattering of a few particles through small angles and very few through larger angles from centre of the atom indicates protons are present at the centre of the atom.
The heavy positively charged central part of the atom is called the nucleus.
Nearly all the mass of the atom is concentrated in the nucleus.