Question

Explain how different observations and experiments led to changes in the atomic model.

Answer 1

Democritus first proposed that the universe is made up of tiny,
indivisible units called atoms
John Dalton carried out scientific experiments that showed that
atoms exist
J. J. Thomson showed that atoms contain smaller particles called
electrons
Ernest Rutherford showed that the positive charge in an atom is
concentrated in a nucleus at its center

Answer 2

http://blogs.bullittschools.org/donnakielman/files/2010/10/The-Development-of-the-ATomic-Theory.pdf