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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. [75] [76] [77] 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).
Balance of nature – superseded by catastrophe theory and chaos theory. 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 His claim that atoms are indestructible is not the reason it is superseded—as it was later scientists who identified the concept ...
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 discoveries of the 118 chemical elements known to exist as of 2025 are presented here in chronological order. The elements are listed generally in the order in which each was first defined as the pure element, as the exact date of discovery of most elements cannot be accurately determined.
In two papers outlining his "theory of atomicity of the elements" (1857–58), Friedrich August Kekulé was the first to offer a theory of how every atom in an organic molecule was bonded to every other atom. He proposed that carbon atoms were tetravalent, and could bond to themselves to form the carbon skeletons of organic molecules.
The work of Democritus survives only in secondhand reports, some of which are unreliable or conflicting. Much of the best evidence of Democritus' theory of atomism is reported by Aristotle (384–322 BCE) in his discussions of Democritus' and Plato's contrasting views on the types of indivisibles composing the natural world. [16]
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.