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The current theoretical model of the atom involves a dense nucleus surrounded by a probabilistic "cloud" of electrons. Atomic theory is the scientific theory that matter is composed of particles called atoms. The definition of the word "atom" has changed over the years in response to scientific discoveries.
1803 John Dalton introduces atomic ideas into chemistry and states that matter is composed of atoms of different weights; 1805 (approximate time) Thomas Young conducts the double-slit experiment with light; 1811 Amedeo Avogadro claims that equal volumes of gases should contain equal numbers of molecules
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.
1963 – Eugene P. Wigner lays the foundation for the theory of symmetries in quantum mechanics as well as for basic research into the structure of the atomic nucleus; makes important "contributions to the theory of the atomic nucleus and the elementary particles, particularly through the discovery and application of fundamental symmetry ...
1904 – J. J. Thomson's plum pudding model of the atom 1904; 1905 – Albert Einstein: Special relativity, proposes light quantum (later named photon) to explain the photoelectric effect, Brownian motion, Mass–energy equivalence; 1908 – Hermann Minkowski: Minkowski space; 1911 – Ernest Rutherford: Discovery of the atomic nucleus ...
Initiated the theory of valency by proposing that each element has a specific "combining power", e.g. some elements such as nitrogen tend to combine with three other elements (e.g. NO 3) while others may tend to combine with five (e.g. PO 5), and that each element strives to fulfill its combining power (valency) quota. 1857: Heinrich Geissler
Boyle was an atomist, but favoured the word corpuscle over atoms. He commented that the finest division of matter where the properties are retained is at the level of corpuscles. Boyle repeated the tree experiment of van Helmont, and was the first to use indicators which changed colors with acidity.
260 BC: Aristarchus of Samos proposes a basic heliocentric model of the universe. [61] 200 BC: Apollonius of Perga discovers Apollonius's theorem. 200 BC: Apollonius of Perga assigns equations to curves. 200 BC: Apollonius of Perga develops epicycles. While an incorrect model, it was a precursor to the development of Fourier series.