Development of The Atomic Theory

By: Madi Jorgensen

Who came up with the first theory of atoms? How long ago?

In the fourth BCE, the first atomic theory was by Greek philosopher Democritus. He suggested that the universe was made of indivisible units called "atoms" which is latin for "atoms". This means that they cannot be divided or cut in any way. Though there was no experimental evidence, he believed that the movements of atoms caused the changes in matter that he had observed. For example if you were to grab a sheet of paper and rip it multiple time you would eventually end up with a small piece that can no longer be ripped into smaller pieces.
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What did John Dalton add to the atomic theory? Why was Dalton’s theory more successful than the previous theory?

Later in 1808 John Dalton, an English schoolteacher proposed a revised atomic theory. He proposed that all atoms of a given element were exactly alike, and atoms of other elements could group together to form compounds. Unlike Democritus, Dalton's theory was based on experimental evidence. For example some scientist tested and found that some substances could combine together in consistent ways. Some of parts of Dalton's work were not correct, but it is considered today to be the foundation of the more modern atomic theory.
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How did J.J. Thomson discover the electron? Describe Thomson’s model of the atom.

About 90 years later in 1897 J.J. Thomson conducted an experiment that proposed that atoms were not indivisible. He was not planning to learn about the atom instead, he was experimenting with electricity. Thomson’s cathode-ray tube experiment advocated that cathode rays were made of negatively charged particles that came from inside atoms. This outcome revealed that atoms could be divided into smaller parts. Thomson's model of the atom had electrons that are spread throughout the atom.
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What is Rutherford’s atomic model? How did he arrive at this model?

Soon, a man named Ernst Rutherford another British scientist created an experiment to test J.J. Thomson's atom model. Two of Rutherford’s students aimed a beam of positively charged alpha particles at a super thin sheet of gold foil. After conducting the experiment Rutherford saw that Thomson's model needed to be revised. He suggested that most of the mass of the atom was concentrated at the atom's center. His model has negative electrons that orbit the positively charged nucleus.
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