Chapter 4 · Atoms and Elements
4.2Indivisible: The Atomic Theory
9 min · two checks
Predict
What did Dalton’s theory say about atoms of the same element?
The idea
- State the useful core of Dalton’s atomic theory.
- Name one idea Dalton had that later evidence changed.
Dalton turned an old philosophical guess into a chemical theory tied to measurements. Elements are made of atoms. Atoms of one element differ from atoms of another. Compounds form when atoms of different elements combine in fixed whole-number ratios. Chemical reactions rearrange atoms; they do not destroy them. That package explains the law of conservation of mass and the law of constant composition.
Parts of the 1808 picture were revised, which is how theories work. Atoms are divisible into protons, neutrons, and electrons. Atoms of one element are not all the same mass, because neutrons can vary (isotopes). Those revisions did not throw out the whole theory. They explained more facts — nuclear charge, radioactivity, average atomic masses — while keeping the claim that chemistry is the rearrangement of atoms.
Keep these
- Compounds: whole-number ratios of atoms.
- Reactions rearrange atoms and conserve them.
- Isotopes and subatomic particles refined, rather than erased, the theory.