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400
Democritus
Discovery- Atoms are invisible, atoms are indestructible, atoms are solid but invisible, atoms are homogeneous, and that they differ in size, shape, mass, position, and arrangement. -
Period: 400 to
Atomic Theory Timespan
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John Dalton
Discovery- All matter is made of atoms, All atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, a chemical reaction is a rearrangement of atoms. -
J.J. Thomson
Discovery- He discovered the electron as being a negatively charged particle within an atom. -
Robert Milliken
He quantified the charge of an electron within an atom. -
Ernest Rutherford
Discovery- He discovered the flaws in Thomson’s model of the atom and discovered the middle of the atom, which was later to be known as the nucleus. -
Niels Bohr
Discovery- He explained why atoms emitted light in fixed wavelengths. -
James Chadwick
Discovery- He discovered that some atoms can have a neutral charge and he named these particles neutrons.
