physics/chemistry question?

Question

why did chadwick look for neutron?why was it hard to find

Answer 1

OK. There was a discrepancy in the atomic mass of elements. We have electrons, which have insignificant mass, and an equal number of protons (to make the atom neutral), but the atomic mass exceeds the sum of the masses of the protons + electrons. So we hypothesize that there is another particle in the atom which has atomic mass roughly the same as a proton but no charge.
It makes sense that this particle is in the nucleus.
BUT, we can't use magnetic properties to isolate this particle. And an atom is pretty much indivisible. So we must actually strip off the electrons AND the protons to isolate neutrons. That's not easy.