Question

The atomic theory has been revised many times over the last several hundred years. John Dalton described the atom as a solid sphere while later scientists such as J.J. Thomson and Ernest Rutherford developed different models of the atom.
Why has the atomic theory changed so much over the last several centuries?
A new scientific method helps scientists form more efficient theories and models.
As new discoveries are made, existing theories are revised or replaced.
The atom has changed over time, and new theories must reflect those changes.
Scientists with different opinions

Answer 1

As new discoveries are made, existing theories are revised or replaced.

Answer 2

The answer is: As new discoveries are made, existing theories are revised or replaced.

Dalton stated that atom is matter that can not be divided.

His "plum pudding" model (1904) suggested: the electrons are embedded in the positive charge.  

J. J. Thomson discovered the electron in 1897.  

According to Rutherford model of the atom:  

1) Atoms have their charge concentrated in a very small nucleus.  

2) Major space in an atom is empty.  

3) Atoms nucleus is surrounded by negatively charged particles called electrons.  

4) An atom is electrically neutral.