While others made important contributions before him, Dalton's work in the early 19th century was groundbreaking. He proposed the following key ideas:
* All matter is composed of atoms.
* Atoms of a given element are identical in size, mass, and other properties.
* Atoms cannot be created or destroyed.
* Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
* In chemical reactions, atoms are rearranged, not created or destroyed.
Dalton's atomic theory provided a simple yet powerful explanation for many chemical phenomena, and it laid the groundwork for future developments in atomic physics and chemistry.
