Inventions & Discoveries · Science and discovery

Atomic theory

1804–1808 · 19th century · Also known as Atomic hypothesis

Atomic theory is the scientific theory that matter is composed of particles called atoms, set out in its modern form by John Dalton, who explained it to Thomas Thomson in 1804 and published his own version in 1808. The idea of indivisible particles appeared in many ancient cultures, but as philosophy rather than science. Dalton held that all atoms of an element have the same weight, that atoms of different elements differ in weight, and that none are created or destroyed in chemical reactions. Physicists later found that atoms have an inner structure.

Atomic theory
Image: John Dalton · Public domain · Wikimedia Commons

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First known
1804–1808
Credited to
John Dalton

NoteThe idea of indivisible particles is ancient, but as philosophy rather than science.

Built onModern chemistry1787
Led toPeriodic table1869

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See also

Cite this entry
APA
The Epoch Institute. (2026). Atomic theory. In The Epoch Institute Encyclopedia. https://the-epoch-institute.org/encyclopedia/atomic-theory
MLA
“Atomic theory.” The Epoch Institute Encyclopedia, The Epoch Institute, 2026, https://the-epoch-institute.org/encyclopedia/atomic-theory. Accessed .
Chicago
The Epoch Institute. “Atomic theory.” The Epoch Institute Encyclopedia. 2026. https://the-epoch-institute.org/encyclopedia/atomic-theory.
Harvard
The Epoch Institute (2026) ‘Atomic theory’, The Epoch Institute Encyclopedia. Available at: https://the-epoch-institute.org/encyclopedia/atomic-theory (Accessed: ).

Last reviewed October 2026Random entry ↻