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History of Atom
Term | Definition |
---|---|
Democritus (400 BCE) | Believed that you would eventually end up with a particle that could not be cut. |
Aristotle (400 BCE) | Disagreed with Deomcritus's theory and thought that such a particle couldn't make up all substances. |
John Dalton (1808) | Published atomic theory and stated that all matter is made of atoms and all atoms of a certain element are identical. However, they are different from atoms of all other elements. Atoms also join with other atoms to form other substances. |
J.J. Thomson (1897) | Found that atoms are made up of even smaller particles. Found particles within the atom that have a negative charge (electrons). Thought that an atom was a positive sphere with electrons mixed through it (plum pudding model). |
Ernest Rutherford (1909) | Suggested that atoms have a nucleus and later found that the nucleus is made up of smaller particles. Called the positively charged particles in the nucleus as protons. |
Niels Bohr (1913) | Agreed that an atom has a positive nucleus surrounded by electrons, but the electrons move around the nucleus in circular paths at a certain distance from the nucleus. (Solar System model (Bohr Model)) |
James Chadwick (1932) | Rutherford's student and discovered that the nucleus contains uncharged particles called neutrons. Also found that the electrons do not move in circular paths, but move with an area around the nucleus called the electron cloud. |