Final answer:
Dalton's atomic theory states that matter is composed of atoms, atoms of the same element have the same mass, atoms of different elements have different sizes, and combinations of atoms create chemical changes.
Step-by-step explanation:
John Dalton's theory of matter, known as Dalton's atomic theory, consists of several key principles.
First, matter is made up of tiny particles called atoms.
Second, atoms of the same element have the same mass. Third, atoms of different elements have different sizes. Lastly, combinations of atoms can create chemical changes.