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History of atom #1.

Democritus proposed that all matter, including space and time, was made up of small units named atoms. He did no experiments and have a little evidence, but his idea was kept on by Lucretius

History of atom #2.

Dalton 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 all atoms of a given element are identical in their mass and properties

History of atom #3.

Mendeleev 1869

He created the periodic table of elements which organizes elements according to their similarities. His Period Law states that "physical and chemical of the elements are periodic functions of their atomic numbers."

History of atom #4.

Eugene Goldstein discovered positive particles in 1885. He noted that the particles had a charge equal opposite to the electron.

History of atom #5.

Henri Becquerel discovered radioactivity in 1896, which earned him a Nobel Prize. Also discovered that rays emitted from uranium caused gases to ionize.

History of atom #6.

J.J. Thompson discovered the electron in 1897. He experimented by testing and studying the nature of electric discharge in a high vacuum cathode-ray tube. He composed a model of the atom to be a spherical object containing electrons confined in a positively charged, jelly-like substance.

History of atom #7.

Ernest Rutherford used the gold foil to discover the modern model of an atom. He concluded that all positive charges were centralized, while negative electrons orbited the nucleus.

History of atom #8.

Millikan used an oil drop experiment to determine the charge of a single electron in 1910.

History of atom #9.

Neils Bohr explained that outer orbits in an atom could hold more electrons than the inner orbits in 1913. 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.

History of atom #10.

Frederick Soddy came up with the concept of isotopes in 1913. He explained with Ernest Rutherford that radiation is due to transmutation of elements.

History of atom #11.

Schrodinger Heisenberg 1925

He thought of the Uncertainty Principle. This principle states that one can never know the exact location and energy of an electron simultaneously.

History of atom #12.

Chadwick discovered the neutron in 1932. The neutron helps balance out protons in the nucleus of an atom.