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Democritus made the first atomic model
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He was recognized one of the most important chemical elements, oxygen.
He stated that during the process of combustion, not only is a substantial quantity of air used, but there is also a visible gain in the mass of the substance. -
September 6, 1766, Eaglesfield, Cumbria, United Kingdom
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It was in 1772 that Lavoisier found out the effects of combustion of phosphorus. He realized that the process required a lot of air and the consequence was a gain in mass.
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The theory of atomism, proposed by Dalton in the early 19th century and derived from meteorological studies, is the foundation for our modern concept of the atom.
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Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.Atoms cannot be subdivided, created, or destroyed. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. In chemical reactions, atoms are combined, separated, or rearranged. -
Dalton developed the law of multiple proportions by studying and expanding upon the works of Antoine Lavoisier and Joseph Proust.
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John Dalton gave this Society the first announcement of his famous atomic theory
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Dalton consolidated his theories of Atomic weight in his New System of Chemical Philosophy (1808–1827).
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July 27, 1844, Manchester, United Kingdom
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December 18, 1856, Cheetham Hill, Manchester, United Kingdom
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April 23, 1858, Kiel, Germany
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March 22, 1868, Morrison, Illinois, United States
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August 30, 1871, Brightwater, New Zealand
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March 14, 1879, Ulm, Germany
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October 7, 1885, Copenhagen, Denmark
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October 20, 1891, Bollington, United Kingdom
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August 15, 1892, Dieppe, France
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J. J. Thomson discovered the electron in 1897
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December 5, 1901, Würzburg, Germany
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Thomson's plum pudding model of the atom in 1904 before the discovery of the atomic nucleus in order to include the electron in the atomic model. In Thomson's model, the atom is composed of electrons surrounded by a soup of positive charge to balance the electrons' negative charges, like negatively charged "plums" surrounded by positively charged "pudding".
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Einstein published
a highly controversial proposal
concerning the nature of light, a
proposal that later formed a
cornerstone of quantum theory -
He published an analysis that pointed the way towards a crucial test of the reality of atoms, and of the validity of the laws of thermodynamics.
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Einstein devised a mathematical method of calculating
the size of atoms and molecules in early 1905 -
A paper on the particulate nature of light, in which he explained the “photoelectric effect” and certain other experimental results by proposing that light interacts with matter as discrete “packets” or quanta of energy, rather than as a wave.
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A paper explaining Brownian motion (the seemingly random movement of particles suspended in a fluid) as direct evidence of molecular action, thus supporting the atomic theory (that all matter is made up of tiny atoms and molecules).
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a paper, which has become known as the Special Theory of Relativity, on the electrodynamics of moving bodies, which showed that the speed of light is independent of the observer's state of motion, and introduced the idea that the space-time frame of a moving body could slow down and contract in the direction of motion relative to the frame of the observer.
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A paper on mass-energy equivalence, in which he deduced the famous equation E = mc2 from his special relativity equations, suggesting that tiny amounts of mass could be converted into huge amounts of energy (which presaged the later development of nuclear power).
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The 1904 Thomson model was proved false by Hans Geiger's and Ernest Marsden's 1909 gold foil experiment.
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His earliest major success was the accurate determination of the charge carried by an electron, using the elegant "falling-drop method"; he also proved that this quantity was a constant for all electrons (1910), thus demonstrating the atomic structure of electricity
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Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny, heavy nucleus.
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He determined that the laws of physics are the same for all non-accelerating observers, and he showed that the speed of light within a vacuum is the same no matter the speed at which an observer travels.
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Next, he verified experimentally Einstein's all-important photoelectric equation, and made the first direct photoelectric determination of Planck's constant h.
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While at the University of Chicago, Robert Millikan worked with one of his graduate students, Harvey Fletcher, to attempt to measure the charge of an electron.
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In 1913, Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities.
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Einstein gave a series of lectures in 1915 about his new theory, which was to become known as the General Theory of Relativity, including a new equation to replace Newton's law of gravity, now known as Einstein's field equation.
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At the time, the wave and particle interpretations of light and matter were seen as being at odds with one another. He suggested that these seemingly different characteristics were instead the same behavior observed from different perspectives that particles can behave like waves, and waves can behave like particles. Broglie's theory became known as the Wave Particle Duality or the De Broglie Hypothesis Basically he suggested that all matter has wave properties.
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He said this means that electrons do NOT travel in neat orbits. Also, all electrons that contain photons will then change momentum and physics.
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Werner Heisenberg contributed to the atomic theory by including quantum mechanics, the branch of mechanics, based on quantum theory, used for interpretating the behavior of elementary particles and atoms.
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In 1932, James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. This particle became known as the neutron.
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October 19, 1937, Cambridge, United Kingdom
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August 30, 1940, Cambridge, United Kingdom
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October 4, 1947, Göttingen, Germany
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December 19, 1953, San Marino, California, United States
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April 18, 1955, Princeton, New Jersey, United States
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November 18, 1962, Copenhagen, Denmark
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July 24, 1974, Cambridge, United Kingdom
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March 19, 1987, Louveciennes, France
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Using his knowledge, he created matrix mechanics, the first version of quantum mechanics in 1925
