Two postulates of Dalton's atomic theory that are still considered correct today are:

• Atoms of different elements have different masses and properties: This is considered the most fundamental and important postulate. 
• Matter is neither created nor destroyed in a chemical reaction: This postulate reflects the Law of Conservation of Mass.

Atom of an element cannot be created, divided, destroyed, or split into smaller particles or transformed into atoms of other elements or transformed into other atoms in a chemical reaction. They are simply rearrangement of new compound. Dalton’s atomic theory based this hypothesis on the law of conservation of mass and on centuries of experimental evidence.