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400
Democritus
In 400 BC, Democritus said matter was formed by different types of tiny particles and all the properties of these particles also determined the properties of matter. Democritus also came up with the idea of everything being composed of matter and thought that solidness depended on the shapes of atomic bits. Democritus also believed that senses were due to touch and the physical existence of atoms encountering each other. -
Line Spectra/ Spectrum
3 types: A continuous spectrum, emission spectrum, and absorption spectrum. (1666 = approximated date because of the constant improvements in experiments and knowledge of spectrums.) -
Julius Lothar Meyer
Created the "first" unofficial period table with 28 elements, yet his work was published after Mendeleev's. He also suggested that the 6 carbon atoms in the benzene ring were connected by only single bonds. His main contribution was his recognition and studying of periodic behavior and patterns, which, in his case, usually consisted of the atomic volume of an element vs the atomic weight of an element. -
Dmitri Mendeleev
In 1869 Dmitri Mendeleev arranged elements into seven groups with similar properties. He classified the building blocks of matter, which is why Dmitri Mendeleev is known as the creator of the offical periodic teacher. He also formulated the periodic law. -
Photoelectric effect
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JJ Thomson
In 1897 JJ Thomson discovered the electron, then in 1904 he suggested a model of an atom as a sphere of positive matter which electrons are positioned by electrostatic forms. He also estimated the value of the electron after his discovery of it. -
Cathode ray tube
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Gold Foil Experiment
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Max Planck
Planck was the intial founder of the Quantum Theory, which helps to develop our understanding of atomic and subatomic particles and processes. He also discovered that light and other electromagnetic waves were emitted from small pockets of energy, called “quanta." Along with this discovery, Planck also spent much time investigating electromagnetic radiation and "black bodies". -
Orbitals
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Plum Pudding Model
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Ernest Marsden
In 1909 Ernest Marsden helped to discover the internal structure of an atom. He was able to discover this with the use of Rutherford's gold foil experiment. -
Oil Drop Experiment
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Robert Millikan
In 1910 Robert Millikan was able to discover the charge of an electron. He was able to discover this with the use of the oil drop experiment. Also coined the term "orbitals." -
Ernest Rutherford
In 1911, Ernest Rutherford discovered that an atom has a small charged nucleus surrounded by a large empty space and are circled by electrons. Also in 1919 he discovered protons along with discovering alpha and beta rays, made the laws of radioactive decay, and identified alpha particles as helium nuclei. -
Bohr's Model
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Louis De Broglie
Broglie was a physicist that predicted the wave nature of electrons. He believed and discovered that electrons can act as both particles and waves, like light. Broglie's ideas and construction of a mathematical system were a basis for developing the wave mechanics theory in quantum mechanics. -
Werner Heisenberg
In 1925 Werner Heisenberg came up with the theory of quantum mechanics. This theory was based on the radiation of electrons. It also helped with his discovery of allotropic forms of hydrogen. -
Erwin Schrödinger
Erwin Schrödinger developed a powerful model of the atom in 1926 that he called the "Electron Cloud Model". He also worked with Werner Heisenburg to mathematically detemine where electrons would be found. -
Cloud chamber/beryllium radiation
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James Chadwick
Discovered the Neutron in his many experiments, made conclusion and proved existence of them in 1932.
Predicted atom would have a neutron, and also figured out that the atomic number of and element is equal to how many protons are in one atom of that element.
