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Period: 460 BCE to 370 BCE
Democritus
He studied natural philosophy in Thrace, Athens, and Abdera, Greece. Democritus adopted his mentor, Leucippus atomic theory, that states that “The universe is composed of two elements: the atoms and the void in which they exist and move. His atomic model was simply a round sphere with no electrons, protons or neutrons. He made the first atomic model, the model contributed for the understanding the idea of the atom -
370 BCE
Leucippus
Leucippus was the founder of Atomism and mentor of Democritus, there is almost no information of his teaching. Leucippus was the first philosopher to affirm of what he was doing, the existence of empty space. He created the atomic theory. There is no even record or confirmation of his birth date. -
Period: to
John Dalton
Dalton's atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties. He based his theory on the law of conservation of mass and constant composition. He states that all matter is made of atoms, wich are indivisible. -
Period: to
Eugine Goldstein
Goldstein contributed drastically in the atomic model and he discovered protons with the experiments he did on cathode rays he also discobvered several properties of cathode rays and that they were emmited perpendicularly from a metal surface. With his model he help scientist picture the atomic model more accuretely. -
Period: to
Joseph John Thomson
In 1897, J.J. Thomson discovered the electron by experimenting with a cathode ray tube, he demostrated that they were negatively charge. He proposed a model of the atom which he likened to plum pudding. The negative electrons represented the raisins in the pudding and the dough contained the positive charge. -
Period: to
Ernest Rutherford
He was a former student of Joseph John Thomson and proved that the Thomson's Plum Pudding structure was incorrect. He performed a series of experiments using alpha particles. Rutherford conclude that the atom consisted in a small positively charge nucleus on the center of the atom surrounded with negative charged electrons. This scientific discovery is considered as the biggest discovery of Rutherford. -
Period: to
Niels Bohr
Niels Bohr was one of the greatest scientist of modern physics, best known for his contribution to the quantum theory and his investigation of the structure of the atoms that won the Nobel Prize. Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. -
Period: to
James Chadwick
Discovered the neutron, using evidence of Irene Joliot-Curie who discovered that when beryllium was bombarded with alpha particle, created a high penetrated power, Chadwick discovered that the beam was not changed for electronic or magnetic fields wich meant that it contained, neutrons. Now the common understanding of an atom was a nucleus that contains protons positively charge and neutral neutrons being in the space of the electrons negatively charge.