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100
Aristotle
Aristotle didn't believe in atoms, He claimed that there was no smallest part of matter and that different substances were made up of fire, air, earth, and water. He couldn't test his theory but everyone knew he was a smart man so they believed him. -
100
Democritus
Democritus came up with the concept of a piece of matter is indivisible. He created the word "atomos" which is where we get the word atom. -
John Dalton
John Dalton proposed that all matter is composed of tiny particles called atoms and that atoms of each element are uniform, which means they have the same compostion. He also stated that atoms of different elements can be told apart by their atomic weights amd atoms can't be created or destroyed in chemical reaction. -
Quantum Model
The first Principal quantum number identifies which energy level in an electron is in. According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This model is based on probability rather than certainty. -
Henri Becquerel
Becqerel discovered radioactivity not on purpose, he accidentally put crystal in the same drawer with photographic paper. This showed radioactive decaying. -
Marie & Pierre Curie
They thought the Atom looked as though it was a planet with many electron rings around them. Their experiments proved that the radiation of Uranium compounds can be measured with precision under determined conditions, and that this radiation is an atomic property of the element of Uranium -
Robert Millikan
Millikan's experiments with atoms led to the discovery of involved electrical charges being carried by electrons. One of his experiments called the "Millikan Oil Drop " won him the Nobel Prize in 1923. In this experiment he accurately determined the electrons charge. -
Ernest Rutherford
Rutherford proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation, proving that the former was essentially helium ions. -
Niels Bohr
Bohr assumed that electrons travel in stationary orbits defined by their angular momentum. Bohr also studied under J.J Thomson. Niels Bohr came up with many equations that described the behavior of certain ions with just one electron orbiting around them. -
James Chadwick
Chadwick is best known for discovering the neutron and that is is found in the nucleus. Chadwick smashed alpha particles into beryllium and allowed the radiation that was released to hit another target: paraffin wax. When the beryllium radiation hit hydrogen atoms in the wax, the atoms were sent into a detecting chamber.The experiment results showed a collision with beryllium atoms would release massive neutral particles, which Chadwick named neutrons. -
J.J Thomson
Thomson discoverd an electron in a number of different experiments from studying electric discharge. He claimed that the model of an atom was a sphere of positive matter where electrons are positioned by electrical force. He also studied positive rays in the the cathode ray tube and discovered that the charge to a mass ratio depended on filling gas in the ray tube.
