He proposed this idea in his atomic theory in the early 1800s, which stated:
* All matter is made up of atoms, which are indivisible and indestructible.
* Atoms of a given element are identical in size, mass, and chemical properties.
* Atoms of different elements have different properties.
* Compounds are formed when atoms of different elements combine in whole-number ratios.
While Dalton's theory has since been refined and expanded upon, his fundamental concept of the atom as the smallest unit of an element retaining its chemical properties remains a cornerstone of modern chemistry.
