Explain what led to the plum pudding model of the atom being replaced by the nuclear model of the atom.

The plum pudding model of the atom was proposed by J.J. Thomson in 1904, based on his discovery of the electron. Thomson suggested that the atom was a sphere of positive charge with electrons embedded in it like plums in a pudding. However, this model was soon found to be inadequate in explaining certain experimental observations, leading to its replacement by the nuclear model of the atom.

One major observation that challenged the plum pudding model was the discovery of alpha particles by Ernest Rutherford in 1899. When Rutherford conducted an experiment where he fired alpha particles at a thin sheet of gold, he observed that some alpha particles were deflected at large angles and some were even reflected back towards the source. This observation could not be explained by the plum pudding model, which predicted that the positive charge was evenly distributed throughout the atom.

Rutherford proposed a new model of the atom in 1911, known as the nuclear model. In this model, he suggested that the atom had a small, dense, positively charged nucleus at its center, with electrons orbiting around it. This model was able to explain the results of Rutherford’s experiment, as the deflection of alpha particles could be attributed to the positively charged nucleus.

The nuclear model of the atom was further developed by Niels Bohr in 1913, who proposed that electrons could only occupy certain energy levels, or shells, around the nucleus. This helped to explain the stability of atoms and the emission and absorption of electromagnetic radiation.

Overall, the nuclear model of the atom replaced the plum pudding model because it better explained experimental observations and was able to provide a more accurate and comprehensive understanding of the structure of the atom.