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1 In many cases atoms of the same element have different masses. Dalton unknowingly based his interpretations on a statistically-weighted average of isotopic masses. 2 This explains the law of constant composition. If all atoms of an element are alike in mass, and if atoms unite in fixed numerical ratios, the percentage composition of a compound must have a unique value, regardless of the size of the sample analyzed. 3 Dalton's theory explains the law of conservation of mass. If the atoms of an element are indestructible, then the very same atoms must be present after a chemical reaction as were present before the reaction. The total mass of reactants and products must be the same. EARLY CHEMICAL DISCOVERIES and the ATOMIC THEORY Laws-Dalton.wpd A. Law of Conservation of Mass Antoine Lavoisier (1743 - 1794) Matter can be neither created nor destroyed in an ordinary chemical reaction. Stated another way, the mass of substances present after a chemical reaction is the same as the mass of
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This note was uploaded on 11/16/2011 for the course CHM 2045 taught by Professor Mitchell during the Fall '07 term at University of Florida.

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