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350
Aristotle
Aristotle (350 B.C.) disagreed with Democritus's model of the atom. Aristotle was a Greek philosopher. He thought that there was no smallest part of matter and that different substances were made of earth, fire, air, and water. Aristotle did not have an atomic model due to the fact that he thought atoms did not exist. -
400
Democritus
Democritus was the first scientist to create a model of the atom. He was the first one to discover that all matter is made up of invisible particles called atoms. He created the name "atom" from the Greek word "atomos", which means uncuttable. He also discovered that atoms are solid, insdestructable, and unique. HIs model was just a round solid ball. Democritus didn't know about a nucleus or electrons, all he knew was that everything is made of atoms. -
John Dalton
John Dalton was an English chemist that created the Atomic Theory of Matter, a collection of previous findings by Democritus and his own findings. He included in this theory that all matter is made of atoms, that atoms cannot be created nor destroyed and also, atoms of different elements combine in whole ratios to form chemical compunds. His theory would later contribute to an advance in the atomic model. -
Sir William Crookes
Sir William Crookes was a British chemist and physicist. He sent a electric current through a tube with gas in it. In the experiment he discovere Cathode Rays. -
JJ Thompson
J.J. Thomson was a very important scientist when it came to the atomic model. Up until his time, all models of the atom looked like a big solild ball. J.J. Thomson discovered the electron, which led him to create the plum pudding atomic model. In this model, he thought that the atom was mostly positive, and negative electrons wandered around the atom. The plum pudding model influenced other scientists to make better atomic models. -
Robert Millikan
Robert Millikan was an American scientist that was very interested in J.J. Thomson's finding of the electron. J.J. Thomson predicted that the electron was 1000 time smaller than the atom. Millikan wanted to prove this hypothesis. He preformed an oil-drop experiment in which he found that J.J. Thomson was correct. Millikan was also involved in the Quantum Theory. Millikan inspired other scientists to explore parts of the atom. -
Ernest Rutheford
Ernest Rutherford was another scientist that changed the atomic model. He felt that J.J. Thomson's model was incorrect, so he created a new one. He created the nucleus, and said that instead of the positive matter being the whole atom, it was just in the middle. He said the atom was mostly empty space and that the electrons surrounded the positive nucleus. This model influenced one of his own students to perfect the atomic model later on. -
Niels Bohr
Niels Bohr was a Danish scientist that was a student of Rutherford. He decided to make a new model based off of Rutherford's model, but changed the orbit of the electron. Also, he created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of the atom. Bohr also created quantum mechanics, his new concept regarding energy. This model is still used to this day. -
James Chadwick
Jame Chadwick was an English scientist that discovered the neutron. Before this discovery, Rutherford had thought that the nucleus was made of positive matter. It made sense that the atom was neutral because the negative electrons and the positive protons cancelled out. But, Chadwick started to question why there was a difference between the atomic mass and the number of protons. Chadwick then found that the missing component was a neutral part. (the neutron)
