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Jan 1, 1000
400 BC - Democritus
Democritus, a greek philosopher, came up with the Atomic Theory. This theory stated that after cutting and object in half over and over agian, eventually you get a particle that cannot be divided. He named this particle an atom. The root word is the Greek word Atomos, meaning "not able to be divided." -
Jan 1, 1000
350 BC - Aristotle
Aristotle, a Greek philosopher, did not agree with Democitus's theiry. He thought that everything could be cut an infinite amount of times. Because of his strong influence on others, most people thought he was right. His theory was not proven false until the 1800's. -
Dalton
Dalton was a very well-known English chemist. Two hundred years later and Dalton's atomic theory is still considered valid. His atomic theory states that all matter is made of indestructible, indivisible atoms, and all atoms of a given element have identical mass and properties. The threory also includes that a compound is made of two or more atoms different atoms being combined, and a chemical reaction is the rearrangent of atoms. -
Thomson
J.J. Thomson was a British scientist. He discovered through several cathode-ray tube expiriments, that there was a flaw in Dalton's theory. He found that atoms have several smaller particles inside them, so an atom can be divided into even smaller parts. -
Rutherford
Ernest Rutherford, a former student of Thomson's , made his first big discovery in 1909. Going off Thomson's idea, Rutherford created an atomic "shooting gallery." In this shooting gallery, a positively charged beam was aimed at a gold sheet of foil that shows where the particles went. It was expected that because he thought atoms was soft matter, that the particles would go straight through. While that was true for most of the particles, some were deflected and some even bounced straight back. -
Rutherford
After reviewing his expiriment is 1909, Rutherford began to rethink the atomic theory. He figured that because not all of the particles went straight through, atoms must be mostly empty space, with a small highly dense area. Rutherford created the idea of the nucleus. To explain why some were reflected, he said that if the positive beam gets too close to the nucleus, it will either be reflected straight back or deflected to the side. -
Bohr
Borh is known as the creator of the Bohr Model. The Bohr Model shows an atom with protons and neutrons occupying the region of the nucleus, with the electrons orbiting around it, much like how the planets orbit the sun. Although the model is not completely correct, it is used as a symbol for atomic energy. -
Schrodinger and Heisenberg
In the 20th century, several physicists added onto the atomic theory. Two of the most important discoveries were made by Austrian Physicist Erwin Schrodinger, and German physicist Werner Heisenberg. They went into greater detail of electrons in the atom. In their expiriments they discovered that there were electron clouds where electrons most likely rest and that electrons have no particular path.
