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Democritus
460 BC 370 BC: Democritus was a Greek philosopher. He was a pupil of Leucippus, who was thought to come up with the first atomic theory. Democritus believed that everything is made of atoms. Atoms cannot be broken up and are in motion. He used our senses to distinguish them from each other. -
John Dalton
Engldand, Early 1800's: Dalton researched gases. His theory was that atoms of the same element are alike and atoms of different elements are different. He discovered that atoms have weight and could be told apart this way. -
JJ Thomson
1898, England: Thomson was best known for the Plum Pudding Model, which was used to explain that most atoms were neutral. His research of the cathode ray led to the discovery of the electron. Up until this time, everyone believed that the atom was the smallest particle. -
Ernest Rutherford
1911, New Zealand: Rutherford discovered the proton through his work in radioactivity. During the Geiger-Marsden experiment, he was looking at the atom. It looked like planets orbiting the sun. He won the Nobel Prize in 1908. -
Niels Bohr
Denmark, 1913: Bohr believed that electrons orbit the nucleus in a circle. He also believed that atoms jumped levels based on energy. His theory worked great for the hydrogen atom, but did not work for any other atom. -
Electron Cloud Model
The electron cloud model is based on two scientists theories, Erwin Shrodinger and Werner Heisenberg. They said that electrons do not move in any particular way, but rather in a floating manner. They called this a cloud.
