John Dalton was a British teacher. He put forward the theory of atoms based on the Law of Conservation of Mass (proposed by Antonie Lavoiser) which states that in a reaction, the reaction mass before and after the same are subscription and Comparative Law Fixed (presented by Josepht Proust) which states that in a pure chemical substance, the ratio of the mass of the element elements in each compound are fixed. For example, is made up of 2 parts water and 1 part H O to form H2O or 1 gram H vs 8 grams of O. Where else would we get water composed of elements with the same ratio.

Dalton's atomic theory includes four (4) as follows:

     Each chemical element arranged on small particles that can not be broken again called atoms. Atoms can not be created nor destroyed during a chemical change. Atoms are round like a ball.
     Constituent atoms of an element are identical in mass (weight) and certain properties. However, atoms of one element differ from the atoms of other elements.
     When forming compounds, different elements joined by a simple comparison. For example, an atom A with an atom B (AB), or one atom A to atom B two (AB2), and so on.
     A chemical reaction is merely a displacement of atoms from one set to the other combinations. Atoms themselves individually and always remains unchanged.

Dalton's atomic theory gives details and a more complete explanation than Democritus statement. But this theory is also not perfect. Why is that? The answer please see Atomic Model: JJ Atomic Theory Thomson.

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