In the early 20th century, many scientists were on the edge of a revolutionary discovery that would reshape our understanding of the atom. The atomic model at that time, known as the "plum pudding" model, proposed by J.J. Thomson suggested atoms as a positively charged "pudding" with negatively charged electrons embedded within it like "plums." However, this model failed to explain certain experimental results associated with the atomic structure of elements.  Therefore, an alpha particle scattering experiment was conducted, which ultimately led to Ernest Rutherford's nuclear model of the atom. In this article, we will learn about the Alpha particle scattering experiment and Rutherford’s nuclear model.

Ernest Rutherford, along with his colleagues Hans Geiger and Ernest Marsden, conducted the alpha particle scattering experiment in 1909. 

The experiment involved directing alpha particles, which are positively charged particles emitted by certain radioactive materials, at a thin (100 nm thickness) gold foil. The ZnS screen was placed behind the gold foil to detect the scintillations. The researchers expected the alpha particles to pass through the gold foil with minimal deflection, as predicted by the prevailing plum pudding model. 

To their astonishment, the results of the experiment were far from what they anticipated. Most of the alpha particles did pass through the gold foil with little to no deviation. A small fraction approximately 1/1000th  exhibited significant deflections because of a very strong positive charge in the centre of the atom. Some even bounced back because of the repulsion of its positive charge with some other positive charge inside the atom.

This unexpected outcome contradicted the predictions of the plum pudding model and hinted at the existence of a concentrated, positively charged nucleus within the atom.

In light of the surprising findings from the alpha particle scattering experiment, Rutherford proposed a new model of the atom in 1911 – the nuclear model. Rutherford's model suggested that the positive charge within an atom is concentrated in a tiny, dense nucleus at its center. The electrons, which are negatively charged, orbit the nucleus at a distance.

The nucleus, according to Rutherford, is incredibly small compared to the overall size of the atom. The majority of the atom's volume is occupied by the empty space through which electrons move. This model successfully explained the results of the alpha particle scattering experiment, as the majority of alpha particles passed through the atom's empty space, while the deflections and rebounds occurred when alpha particles came close to the positively charged nucleus.

Moreover, the model allowed scientists to estimate the charge of the nucleus, which turned out to be positively charged and responsible for the observed deflections of the alpha particles.