The atoms of Democritus and those of Dalton

Marginal observations on the properties of matter

Abstract

Chemical atomism and physical atomism are not the same thing. Physical atomism is concerned with the ultimate composition and structure of the matter, up to "simple particles". On the contrary, chemical atomism (Dalton 1804) is restricted only to the smallest particles capable of showing chemical properties. Democritus atoms resemble perhaps the modern subnuclear particles. Several philosophers contrasted the assumption that atoms cannot be further divided, since there is no logical reason to stop at any level the spitting process. The missing scientific theory was proposed by Dalton: the ultimate matter is constituted by "elements" with different weight and chemical properties, and the smallest part of each element, capable of existing without losing its chemical properties, may be called atom. Dalton's atoms remain unaltered in all chemical reactions. If they are further split, they lose their chemical properties. Chemical atomism avoids any hypothesis on the ultimate structure of the matter. The origin of matter properties is further discussed, in connection to the atomic structure and law of mass conservation in chemical reactions. Furthermore, Greek and medieval theories on the structure of the matter are shortly discussed: alchemy, flogist, vitalism.