Chemistry / Unit 2 Chem 0181 short lesson, about 20 seconds
Dalton's Atomic Theory
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The idea
Dalton's 1807 atomic theory holds that matter is made of indivisible atoms, each element's atoms identical in mass and unchanged by reactions.
In practice
Copper keeps its atomic identity through every chemical change, so heating it alone never produces a different, simpler substance.
Where people slip
Dalton called atoms indivisible; later discoveries added subatomic particles without discarding his other four postulates.
Your place on the trail
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