In 1804, John Dalton proposed the existence of atoms. He not only postulatedthat atoms exist, as had ancient Greek philosophers, but he alsoattributed certain properties to the atom. His postulates were as follows:1. Elements are composed of indivisible particles, called atoms.2. All atoms of a given element have the same mass, and the massof an atom of a given element is different from the mass of an atom ofany other element.3. When elements combine to form compounds, the atoms of one elementcombine with those of the other element(s) to form molecules.4. Atoms of two or more elements may combine in different ratiosto form different compounds.
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