The spectrum of the N2 molecule shows that the nitrogen atom is a fermion, or cq

Question

The spectrum of the N2 molecule shows that the nitrogen atom is a fermion, or cquivalently that the nitrogen nucleus (4N) is a boson. Before the discovery of the neutron, it was believed that nuclei contained protons and "internally bound" electrons. The 4N nucleus was known to have a mass of about 14 proton masses and a charge of +7 elementary charges. Show that the "trapped electron" theory predicts (incorrectly) that the nitrogen atom is a boson. This was one of the first solid pieces of evidence that the neutron existed.

Explanation / Answer

The nitrogen atom is electrically neutral.
The atomic number of N is 7. Hence there are 7 number of electrons in various electronic shell outside the nucleus.
Also, since the mass number of N is 14, there exists a total of 14 elementary particles inside the nucleus each having mass equal to(nearly) that of the proton.
Hence it was assumed that there are a total of 14 protons inside the nucleus.
But a serious problem arises now- the conservation of charge fails! The whole atom becomes electrically positive.
In order to deal with this awkward and unrealistic situation the ‘trapped electrons’ theory came into play. It is assumed that there are extra 7 electrons inside the nucleus in addition to the 14 protons so that the whole atom becomes electrically neutral.
So, if we talk about the nucleus of N, there are majority of bosons. Hence the nucleus acts like boson.
On the other hand the spectrum arises due the electrons in the outer shells and they are fermions.
So in the spectroscopic point of view the whole N atom acts as fermions.

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