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Chemistry LibreTexts

Atomic Theory

Atomic theory states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity. It began as a philosophical concept in ancient Greece (Democritus) and India and entered the scientific mainstream in the early 19th century. It was during this time when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of particles.