AAT Bioquest

What is the basis for Dalton’s Atomic Theory?

Posted December 13, 2022


The first part of Dalton’s atomic theory states that all matter is made up of atoms, which are indivisible. The second part of the theory states that all atoms of a given element are identical in mass and properties. The third part states that compounds are combinations or two or more different types of atoms. And the fourth part states that a chemical reaction is simply a rearrangement of atoms. 

Dalton’s Atomic Theory is based on two laws – The Law of Conservation of Mass and the Law of Constant Composition. This was the first theory that successfully described all matter in terms of atoms and their properties. The law of conservation of mass states that matter is neither created nor is it destroyed in a closed system. This means that in a chemical reaction, the amount of each element in the end product must be the same as in the starting materials. The law of constant composition states that the proportion of individual elements will always remain the same in a pure compound. For example, sodium chloride or salt, which has the molecular formula NaCl, will always have the same proportions of sodium (Na) and chlorine (Cl), regardless of the quality of salt or where it was obtained from.

Additional resources

John Dalton and the origin of the atomic theory: reassessing the influence of Bryan Higgins

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