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Democritus (/ d ɪ ˈ m ɒ k r ɪ t ə s /, dim-OCK-rit-əs; Greek: Δημόκριτος, Dēmókritos, meaning "chosen of the people"; c. 460 – c. 370 BC) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. [2] Democritus wrote extensively on a wide ...
Rutherford defined this position as being the element's atomic number. [73] [74] [75] In 1913, Henry Moseley measured the X-ray emissions of all the elements on the periodic table and found that the frequency of the X-ray emissions was a mathematical function of the element's atomic number and the charge of a hydrogen nucleus (see Moseley's law).
Progression of atomic theory. Democritus, the originator of atomic theory, held that everything is composed of atoms that are indestructible. His claim that atoms are indestructible is not the reason it is superseded—as it was later scientists who identified the concept of atoms with particles, which later science showed are destructible.
Atomic theory (early) Democritus (c. 460 – c. 370 BC) [62] Founder of atomism in cosmology. Atomic theory (modern) Father Roger Boscovich (1711–1787) [63] First coherent description of atomic theory. John Dalton (1766–1844) [64] First scientific description of the atom as a building block for more complex structures. Atomic bomb
The possibility of a vacuum was accepted—or rejected—together with atoms and atomism, for the vacuum was part of that same theory. Democritus and Lucretius denied the impossibility of a vacuum, being of the opinion that there must be a vacuum between the discrete particles (atoms) of which, they thought, all matter is composed.
With the rise of scholasticism and the decline of the Roman Empire, the atomic theory was abandoned for many ages in favor of the various four element theories and later alchemical theories. The 17th century, however, saw a resurgence in the atomic theory primarily through the works of Gassendi, and Newton.
An image from John Dalton's A New System of Chemical Philosophy, the first modern explanation of atomic theory.. This timeline of chemistry lists important works, discoveries, ideas, inventions, and experiments that significantly changed humanity's understanding of the modern science known as chemistry, defined as the scientific study of the composition of matter and of its interactions.
1906 Charles Barkla discovers that each element has a characteristic X-ray and that the degree of penetration of these X-rays is related to the atomic weight of the element; 1908-1911 Jean Perrin proves the existence of atoms and molecules with experimental work to test Einstein's theoretical explanation of Brownian motion