In atomic physics, which scientist is credited with the discovery of the neutron as a neutral particle inside the atomic nucleus?

Introduction / Context:
This question belongs to the history of atomic structure. It asks who discovered the neutron, the neutral particle inside the atomic nucleus. Knowing which scientists are associated with the electron, proton and neutron helps you understand how our model of the atom developed over time.

Given Data / Assumptions:

• We are looking for the scientist who first identified the neutron.
• Options include J. J. Thomson, James Chadwick, Ernest Rutherford, Joseph Priestley and Niels Bohr.
• The neutron is an electrically neutral particle found in atomic nuclei, except for the most common hydrogen isotope.
• We assume standard historical information from physics and chemistry textbooks.

Concept / Approach:
The neutron was discovered significantly later than the electron and proton because it carries no electric charge and therefore is harder to detect with early instruments that relied on electric and magnetic fields. James Chadwick performed experiments in 1932 using beryllium bombarded with alpha particles, which emitted a penetrating radiation. By careful analysis, he showed that this radiation consisted of neutral particles with mass roughly equal to that of the proton, and he named them neutrons. This work completed the basic picture of the atomic nucleus as composed of protons and neutrons.

Step-by-Step Solution:
1) Recall that J. J. Thomson is famous for the discovery of the electron through cathode ray experiments.2) Ernest Rutherford is known for the discovery of the atomic nucleus and the proton through alpha scattering and related experiments.3) Joseph Priestley discovered oxygen gas and made contributions to early chemistry, not directly to nuclear particles.4) Niels Bohr proposed the planetary model of the atom with quantised orbits but did not discover the neutron.5) James Chadwick, in 1932, bombarded beryllium with alpha particles and detected neutral particles knocking protons out of paraffin wax.6) From the behaviour of this radiation, Chadwick concluded that it consisted of neutrally charged particles with mass similar to that of protons and named them neutrons.7) Therefore, the discovery of the neutron is credited to James Chadwick.

Verification / Alternative check:
Standard physics histories state that Rutherford had proposed the existence of a neutral nuclear particle earlier, to explain the discrepancy between atomic number and atomic mass, but he did not observe it experimentally. Chadwick experiment provided the direct evidence needed. The discovery of the neutron allowed better understanding of isotopes and nuclear reactions, and for this work Chadwick received the Nobel Prize in Physics in 1935. These details confirm that the correct answer is James Chadwick, not the other listed scientists.

Why Other Options Are Wrong:
J. J. Thomson: Discovered the electron and measured its charge to mass ratio, but he did not identify the neutron.
Ernest Rutherford: Proposed the nuclear model and identified the proton but only hypothesised the existence of neutrons.
Joseph Priestley: Worked in gaseous chemistry and discovered oxygen, unrelated to nuclear particles.
Niels Bohr: Developed the quantum model of the hydrogen atom, explaining spectral lines, but did not discover the neutron.

Common Pitfalls:
Students sometimes confuse Rutherford name with every nuclear concept because he is strongly associated with the nucleus. However, while Rutherford suggested that a neutral nuclear particle should exist, it was Chadwick who actually discovered it experimentally. Another error is to choose Thomson by mistakenly associating all subatomic particle discoveries with one scientist. To avoid confusion, link each scientist to one major discovery: Thomson for electrons, Rutherford for the nucleus and proton, and Chadwick for neutrons.

Final Answer:
The neutron was discovered by James Chadwick.