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Father of modern atomic theory; five parts of his atomic theory including that elements are
composed of atoms and that element’s atoms are identical in mass.

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Dismissed Democritus’ atom as “worthless.” Said that the four elements were earth, fire, air and
water.

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Mid 300’s B.C.

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Aristotle did not believe in the atomic theory. He believed that all things, materials were made from the four elements. The four elements consisted of fire, earth, water, and air. He did not agree with the belief that the universe was made up of atoms.

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Was the first person to identify the possibility of an atom

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Approx. 400 B.C.

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Although Democritus did not discover a atomic model, he formed the belief that “atoms were uniform, solid, hard, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped.”

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Said that an atom has a small positive nucleus and the remainder is empty space. Predicted the
existence of neutrons.

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1912

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Rutherford discovered the nuclear atom model. Rutherford illustrated the atom as having a tiny, dense, and positively charged core called the nucleus. Rutherford stated that the mass of the atom is concentrated in its nucleus.

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Discovered the neutron

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1939

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When Chadwick discovered the neutron the cloud model was revised. The revised version of the cloud model is sometimes referred to as the James Chadwick atomic model by scientists.

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1803, 1805, 1808

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John Dalton discovered the Billiard Ball Model. Dalton described  an atom to be a ball-like structure, as the concepts of atomic nucleus and electrons were unknown at the time. John Dalton's atomic theory stated that all matter was comprised of indivisible and indestructible atoms with distinct masses and properties.

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Discovered the electron.

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1897

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J.J. Thomson discovered the Plum Pudding Model. The model proposed that atoms contained small negatively charged electrons.

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Predicted that electrons travel in specified energy levels.

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1911, 1915, 1918

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Bohr discovered the Bohr model. This model proposed that electrons traveled around the nucleus. The Bohr model is a structural model of an atom, and is also known as the Planetary model.

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Came up with the “uncertainty principle”, which stated that it is impossible to determine the
position and momentum of a particle at the same time.

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1927

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Werner Heisenberg discovered the Quantum Mechanical model. This model defined the possibility of putting electrons within an atom by describing the principal energy level, energy level, orbital, and spin. His theory stated that matter has wav-like properties, which his model was based off of.

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GCSE Physics - Development of the model of the atom  #31

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GCSE Physics - Development of the model of the atom