Which postulate of Dalton's atomic model was later changed and why

Dalton's atomic theory had some drawbacks. The indivisibility of an atom was proved wrong: an atom can be further subdivided into protons, neutrons and electrons. However an atom is the smallest particle that takes part in chemical reactions.

The postulate was that atoms cannot be subdivided, which was changed later because atoms can be subdivided into protons, neutrons, and electrons.