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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.
Sir Alexander Fleming FRS FRSE FRCS [2] (6 August 1881 – 11 March 1955) was a Scottish physician and microbiologist, best known for discovering the world's first broadly effective antibiotic substance, which he named penicillin.
He described atomic theory as a 'Thoroughly materialistic bit of joiners work'. [77] English chemist Alexander Williamson used his Presidential Address to the London Chemical Society in 1869 [78] to defend the atomic theory against its critics and doubters. This in turn led to further meetings at which the positivists again attacked the ...
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.
1927: Georges Lemaître: Theory of the Big Bang; 1928: Paul Dirac: Dirac equation (Quantum mechanics) 1929: Edwin Hubble: Hubble's law of the expanding universe; 1929: Alexander Fleming: Penicillin, the first beta-lactam antibiotic; 1929: Lars Onsager's reciprocal relations, a potential fourth law of thermodynamics
Thomson's model marks the moment when the development of atomic theory passed from chemists to physicists. While atomic theory was widely accepted by chemists by the end of the 19th century, physicists remained skeptical because the atomic model lacked any properties which concerned their field, such as electric charge, magnetic moment, volume, or absolute mass.
By this time the Ernest Rutherford model of the atom had been published, [21] [22] but much of the discussion involving atomic structure revolved around the quantum model of Arthur Haas in 1910. Also, at the Solvay Congress in 1911 Hendrik Lorentz suggested after Einstein's talk on quantum structure that the energy of a rotator be set equal to nhv.
In seeking to explain atomic spectra, an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this yield a better overall description, i.e. the atomic orbital model, but it also provided a new theoretical basis for chemistry (quantum chemistry) and spectroscopy. [2]