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Chemistry
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Updated:
12 Nov 2019
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obenma
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Events
James Chadwick discovers the neutron in atoms. (1932)
The Gold Foil Experiment. scientists discovered that every atom contains a nucleus where all of its positive charge and most of its mass are concentrated. (1908)
When J J Thompson discovered electrons and suggested that the model of an atom was a sphere of matter in which electrons are positioned by electrostatic forces. 1897
Democritus creates atomic theory and illustrated the first drawing of his atomic theory. (370 BC)
John Dalton proposes that all matter is made of atoms. Postulated that chemical reactions are the result of rearranging of reacting atoms (1803)
Cathode Ray Tube Experiment Was used to discover electrons by J.J Thompson (1897)
Antoine Lavoisier Proposed the definition of an element in the book “Elements of Chemistry” (1789)
Plum Pudding Model Pitched by J.J Thompson in 1904. Was a model that proposed the idea that atoms had the shape of a plum pudding with negative charged electrons embedded into a positively charged substrate. This was later proved incorrect.
Bohr Planetary Model a planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus. Was only accurate with only one electron elements (1913) Henry Moseley Made Moseley’s law, which states that the frequency of x-ray radiation has a mathematical relationship to an element's atomic number. (1913)
Robert Millikan discovers the value for an electron charge. (Experiments began in 1909)
Erwin Schrodinger develops the Electron Cloud Model Informal term for the quantum mechanical model, a simplification of showing the probable locations around an atom where electrons are found (1926)
Law of conversation and mass developed which states that mass can’t be created or destroyed by chemical reactions or physical transformations (1789)
Dalton’s Atomic Theory Theory that all matter is composed of atoms, and that different elements have atoms of different size and mass. (First presented in 1803, published as part of a book in 1808)
Rutherford Model Alternative to plum-pudding model, believed that atoms had a small central nucleus and a cloud of orbiting electrons taking up most of the atom’s space (1911)
Quantum mechanical model created by Erwin Schrödinger Uses complex orbitals, called electron clouds, to represent the probable location of an electron in an atom (1926)
Ernest Rutherford Did the gold foil experiment to disprove the plum pudding model, created the model of electrons orbiting a tiny positively charged nucleus (1911)
Niels Bohr develops the idea that electrons move in set orbits around an atom (1903)
Periods
Timeline of The Atomic Model
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