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350
BCE Aristotle
Aristotle did not believe in atoms he thought that everything was made up of 5 basic elemnets. These elements were air, water, fire, and earth. He said that everything had a little bit of some of these things. -
400
BCE Democratis
Democratis is credited for creating atomic theory he wondered what would happen if you broke something half and then in half again until you could not split it half anymore. He called this an atom. -
Oct 20, 700
Alchemy Begins
Alchemist built of of aristotle's theory of everything was made up of air, water, fire, and earth. They thought that is those things made everything then they could make gold or potions with the right amount of the original elements. They were also able to discover hydrochloric acid, nitric acid, potash, and sodium carbonate. -
American Revolution
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John Dalton
John Dalton's theory was all elements have an atom and all atoms of an element are the same. The difference between elements is the mass of their atom. -
American Civil War
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Dimitri Mendeleev
Dmitri Mendeleev created the first Periodic table where elements were organized by their atomic mass. The were also organized by similar properties. -
J.J. Thomson
J.J. Thomson discovered the first subatomic particles proving that atoms were not the smallest things. J.J. Thomson discovered electrons and concluded that atoms were made up of negative particles and positive cores. His model was a plum pudding where the electrons were the plums and the pudding was the positively charged soup. -
Hans Geiger
Hans Geiger invented the Geiger Counter. The Geiger Counter measure alpha and beta particle to measure radioactivity. -
Robert Millikan
He determined the charge of an electron by the oil drop method. The oil drop experiment was when he dropped a tiny amount of oil onto a negatively charged metal it floated in the air. By this he determined that an electrons were negative. He also determined that all electrons have the same charge. -
Ernest Rutherford
Ernest Rutherford discovered that atoms had a nucleus. He shot alpha rays which he discovered earlier and shot them through an atom and they bounced of of something in the middle this was the nucleus. He later discovered the proton. He discovered the proton by splitting an atom and looking at the pieces. -
World War One
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Niels Bohr
Niels Bohr developed a model of the atom that is still used today for education purposes. In this model electrons are located on different energy levels or shells. Chemical properties were determined by only the ones in the outer orbit. He also discovered that an electron could drop to a lower shell by emitting a photon. -
James Chadwick
James Chadwick studied under Ernest Rutherford and tried to study the atom with him. He had a hypothesis that there was a neutral particle in the atom but no one had found it. He used other methods of tracking the radiation and discovered a neutron. The neutron had slightly more mass than a proton and had no charge. -
World War Two Begins
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Dimitri Mendeleev
Dmitri Mendeleev created the first Periodic table where elements were organized by their atomic mass. The were also organized by similar properties.