Atom has a very small nucleus at the centre. There is large empty space around the nucleus. Entire mass of an atom is concentrated in a very small positively charged region which is called the nucleus. Electrons are distributed in the vacant space around the nucleus.

The observations made by Rutherford led him to conclude that: A major fraction of the α-particles bombarded towards the gold sheet passed through the sheet without any deflection, and hence most of the space in an atom is empty.

Physicist Ernest Rutherford established the nuclear theory of the atom with his gold-foil experiment. When he shot a beam of alpha particles at a sheet of gold foil, a few of the particles were deflected. He concluded that a tiny, dense nucleus was causing the deflections.

Almost all the alpha particles did pass through the foil. Some alpha particles were deflected off at different angles as observed at the screen of the detector. Very few of the alpha particles (one or two) even bounced backwards after hitting the gold foil.

Following were the observations made by Rutherford: Most of the alpha particle passed straight through the foil without any deflection from their path. A small fraction of them were deflected from their original path by small angles. Only a few particles bounced back.