Question

why was it necessary to consider the existence of neutrons in the nucleus of an atom

Answer 1

Its main job is to hold together the subatomic particles of the nucleus (protons, which carry a positive charge, and neutrons, which carry no charge. ... This is where the strong nuclear force comes in. The strong nuclear force is created between nucleons by the exchange of particles called mesons.

Answer 2

Neutrons are very important in providingstability for an atom. Some atoms don't "need" neutrons - The hydrogen atom does not have any neutrons. However, as the atomic number ( # of protons ) increases, the number of neutrons increases as well.