Scientists sometimes replace one scientific model with a different model - AQA - GCSE Physics - Question 10 - 2018 - Paper 1

The plum pudding model of the atom, proposed by J.J. Thomson, depicted the atom as a homogeneous sphere of positive charge with negatively charged electrons embedded within it, similar to plums in a pudding. However, several experiments showed inconsistencies with this model, ultimately leading to the adoption of the nuclear model.

1. Alpha Particle Scattering Experiment: In 1909, Ernest Rutherford conducted the alpha particle scattering experiment, where alpha particles were directed at a thin gold foil. According to the plum pudding model, particles should have passed through with minimal deflection due to the diffuse positive charge.

2. Observation of Deflections: Surprisingly, while most alpha particles passed straight through, a few were deflected at large angles. This observation implied that a significant portion of the atom was empty space, challenging the structure suggested by the plum pudding model.

3. Concentration of Mass: Rutherford concluded that the mass of the atom is concentrated at a small central region (the nucleus), which is positively charged, contrary to the even distribution in the plum pudding model.

4. Conclusion of Nucleus: Therefore, the nuclear model replaced the plum pudding model because it effectively explained the observations from experiments, specifically the central nucleus and empty space surrounding it, illustrating a more accurate representation of atomic structure.