Rutherford determined that such a zero-charge particle would be difficult to detect by available techniques. By 1921 Rutherford and William Harkins had independently named the uncharged particle the neutron, while about that same time the word proton was adopted for the hydrogen nucleus.

Introduction

The discovery of neutrons played a crucial role in the development of our understanding of the structure of the atom. However, at the time of Rutherford's experiment, neutrons were not yet known. This can be understood by examining the experiment and the various models of the atom that were proposed during that time.

Rutherford's Experiment

Rutherford's famous experiment involved firing alpha particles at a thin gold foil and observing their deflection. According to the prevailing model at the time, known as the Thomson model, atoms were thought to be composed of a positively charged "pudding" with embedded negatively charged electrons.

The Thomson Model

The Thomson model, also known as the plum pudding model, proposed that the atom was a uniform, positively charged sphere with embedded electrons. In this model, there was no mention or knowledge of neutrons. According to this model, the alpha particles were expected to pass through the gold foil with little to no deflection.

Observations and Conclusions

However, Rutherford's experiment yielded unexpected results. Some alpha particles were deflected at large angles, and a few even bounced back. This led Rutherford to propose a new model for the atom, known as the nuclear model.

The Nuclear Model

In the nuclear model, Rutherford suggested that the atom consisted of a small, dense, positively charged nucleus at the center, surrounded by a cloud of negatively charged electrons. This model explained the observations from the gold foil experiment, as the deflection and bouncing back of alpha particles could be attributed to their interaction with the positively charged nucleus.

Discovery of Neutrons

It was not until later, in 1932, that the existence of neutrons was discovered by James Chadwick. Chadwick observed that certain types of radiation could penetrate materials that were impenetrable to alpha particles and beta particles. He concluded that there must be a neutral particle with a mass similar to that of a proton present in the atomic nucleus. This particle was named the neutron.

Conclusion

In summary, at the time of Rutherford's experiment, neutrons were not yet known. The prevailing model, the Thomson model, did not account for the unexpected observations from the gold foil experiment. It was only later, with the discovery of neutrons by James Chadwick, that our understanding of the structure of the atom was further refined.