Dalton's atomic theory states four critical truths about atoms: firstly, everything is made up of atoms and atoms cannot be destroyed. Secondly, all atoms within a single element are identical. Thirdly, compounds are formed from two or more different kinds of atoms. Finally, chemical reactions rearrange atoms.
Dalton made his atomic theory public in 1803, making him the first scientist in history to develop an accurate understanding of atoms. Though his theory remains valid today, scientists have since qualified his theory to match more recent discoveries. Advancements of Dalton's theory have proven that atoms can be destroyed by nuclear reactions and that some elements contain atoms called isotopes that have varying masses.