New experimental evidence may lead to a scientific model being
changed or replaced.
Before the discovery of the electron, atoms were thought to be tiny
spheres that could not be divided.
The discovery of the electron led to the plum pudding model of the
atom. The plum pudding model suggested that the atom is a ball of
positive charge with negative electrons embedded in it.
The results from the alpha particle scattering experiment led to the
conclusion that the mass of an atom was concentrated at the centre
(nucleus) and that the nucleus was charged. This nuclear model
replaced the plum pudding model.

Niels Bohr adapted the nuclear model by suggesting that electrons
orbit the nucleus at specific distances. The theoretical calculations of
Bohr agreed with experimental observations.
Later experiments led to the idea that the positive charge of any
nucleus could be subdivided into a whole number of smaller particles,
each particle having the same amount of positive charge. The name
proton was given to these particles.
The experimental work of James Chadwick provided the evidence to
show the existence of neutrons within the nucleus. This was about
20 years after the nucleus became an accepted scientific idea.