Long ago in the 5th Century BC, Leucippus and Democritus inferred that all living and inanimate things were composed of indivisible and invisible particles called atoms.
Democritus believed that there was a smallest particle— “atomos” that made up all of nature.
The history of the atomic theory from the early1700s to the late-1800s is a tapestry of debate about the meaning of data, partial theories, anomalies and incommensurabilities.
There were revolutions in particle thinking and the major revolution in atomic thought is attributed to John Dalton - indeed, Dalton's theory "marks an epoch in the history of chemistry".
Experiments in the eighteenth and nineteenth centuries led to an organized atomic theory by John Dalton (1766-1844) in the early 1800s, which explained several laws known at that time:
– The law of constant composition
– The law of conservation of mass
– The law of multiple proportions
In Dalton’s Atomic Theory (published in 1808), atoms
• Each chemical element is composed of extremely small particles that are indivisible and cannot be seen by the naked eye, called atoms.
• Atoms of an element are similar and different from other elements.
• Compounds are the result of a combination of two or more different kinds of atoms
• Atoms are rearranged to form new combinations in a chemical reaction.
Not until the beginning of the 20th century the atomic theory was finally proved as a fact, not a mere hypothesis. It was accomplished by skilful experiments of the French physicist Jean Baptiste Perrin (1870-1942).
Dalton’s Atomic Theory
