Although two centuries old, Dalton's atomic theory remains valid in modern chemical thought.
All matter is made of atoms.
Atoms are indivisible and indestructible. Compounds are formed by a combination of two or more different kinds of atoms. A chemical reaction is a rearrangement of atoms. Modern atomic theory is, of course, a little more involved than Dalton's theory but the essence of Dalton's theory remains valid. Today we know that atoms can be destroyed via nuclear reactions but not by chemical reactions.