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460 BCE
Democritus(460-370B.C.E) Leucippus (5th century B.C.E)
Democritus and Leucippus both propose that Matter is composed of atoms separated by empty space through which the atoms move, atoms are solid, homogeneous, indivisible, and unchangeable, all apparent changes in matter result from changes in the groupings of atoms, there are different kinds of atoms that differ in size and shape, and the properties of matter reflect the properties of the atoms the matter contains. -
John Dalton(1766-1844)
Agreed that all matter was created by atoms, which he believed were indestructible. He also stated that compounds are created by combining two atoms, and that atoms of given elements are identical in their mass and properties. -
Eugene Goldstein
Discovered positive particles. He noted that the particles had a charge equal and opposite to the electron. -
J.J Thompson (1856-1940)
Discovered the electron. He experimented by testing and studying the nature of electric discharge in a high vacuum cathode-ray tube. -
Ernest Rutherford(1871-1937)
Used the gold foil experiment to discover the modern model of an atom. He concluded that all positive charges were centralized, while negative electrons orbited the nucleus. -
Robert A. Millikan(1868-1953)
Used an oil drop experiment to determine the charge of a single electron. -
Niels Bohr(1885-1962)
Explained that outer orbits in an atom could hold more electrons than the inner orbits. By knowing this, one can determine the atom's chemical properties. He also gave birth to the idea that electrons emit light by jumping orbits. -
Werner Heisenberg(1901-1976)
Thought of the Uncerainty Principle. This principle states that one can never known the exact location and energy of an electron simultaneously. -
Frederick Soddy(1877-1956)
Came up with the concept of isotopes. Explain with Ernest Rutherford that radiation is due to transmutation of elements. -
James Chadwick(1891-1974)
Discovered the neutron. The neutron helps balance out protons in the nucleus of an atom.
