Physics and Chemistry


When was the first atomic theory proposed?

John Dalton (1766–1844), an English natural philosopher, chemist, physicist, and teacher, developed the concepts of an atomic theory in the early nineteenth century. He published A New System of Chemical Philosophy in 1808. His main concepts of atomic theory may be summarized as:

  • All matter—solid, liquid and gas—consists of tiny, indivisible particles called atoms.
  • All atoms of a given element have the same mass and are identical, but are different from the atoms of different elements.
  • Chemical reactions involve the rearrangement of combinations of those atoms, not the destruction of atoms.
  • When elements react to form compounds, they combine in simple, whole-number ratios.


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