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400
Democritus discovers the atom and creates an atomic model.
In 400 BC Democritus created a model of a round spherical atom with no protons, neutrons, or electrons. -
JJ Thomson discovers the elctron
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John Dalton creates a new theory.
His atomic theory was: All matter is made of invisible and indestructible atoms. Atoms of any given element are identical in mass and properties. Compounds are formed by 2 or more different types of atoms. A chemical reaction is the rearrangement of atoms. -
JJ Thomson makes a new atomic model
In 1904 Thomson suggested a new model of a sphere with a positive charge and negative electrons positioned outside of it. -
Ernest Rutherford atomic model and structure
In 1907 he also discovered elements atomic number. He discovered the atomic nucleus. -
Niels Bohr atomic theory and model
His theory was that an atom contains positive nucleus and negatively charged electrons orbiting the nucleus. -
Robert Millikan atomic theory
In 1913, Millikan dicovered that atoms have a negative charge in them. -
James Chadwick discovers the neutron
In 1932 Chadwick discovered the neutron, a neutron has a neutral charge, and that it is found in the nucleus of an atom.
