Neutrons and the Bohr Atom
Although there was now a great deal of experimental evidence to support the latest atomic model, there were still one or two elements which did not fit exactly into the picture. It was not until 1933 that this mystery was solved.
In that year, the physicist James Chadwick, one of Rutherford's research workers, discovered that the nucleus contained another particle of matter which, unlike the proton, possessed no electric charge but was very nearly the same mass. This new particle, the neutron, was the missing link which enabled the whole of the Periodic Table of the elements to be explained in terms of the so-called fundamental particles of matter. From a chemical point of view, at least, the model appeared to be complete and scientists accepted this model of the atom as a 'good working likeness'.
Like all other attempts, it proved in the end to be inadequate, and was replaced by an even more complex model. Although the Bohr atom is now considered not accurate enough, it is a helpful aid in the understanding of many chemical and physical changes, and can act as a useful model, providing it is not mistaken for the real thing.