Question

Why a free proton in nuclear physics is always assigned by 1H1(mass no 1 &atomic no1) and whenever proton mass is used,mass of 1H1 is written, what is the reason?

Answer 1

The reason for that is simple....

Explanation:

We know that a hydrogen-atom is composed of a proton and an electron. It is written by `""_1^1H` or just `""^1H` in isotope notation.

Since the electron's mass is negligible, the total mass of the hydrogen atom will be just a proton, i.e.

`m_(""^1H)=m_p`, where `p` is the proton.

So, a free proton would also have the mass of a hydrogen atom. Therefore in some cases, instead of writing `p` we can just write the hydrogen atom, since they both have the same mass anyway.