-
200
440 BC - Democritus
He thought that you would eventually end up with a particle that can not be cut, He called this particle"atom." -
200
382 BC - Aristotle
He disagreed with Democritus. He thought you would never get down to a particle you could not cut. He was incorrect -
late 1700's - Dalton
He thought that all substances are made up of atoms. Atoms of the same element are exactly alike. Atoms can join with others to make new substanes. -
1897 - JJ Thomson
His theory showed mistakes in Dalton's theory. Discovered small particles inside the atoms. He discovered negatively charged particles and called them elecrons. (Plums in the plum pudding) -
20th century - Schrodinger and Heisenberg
Futher explained the movement of electrons in the atom. Electron Clouds -
1909 - Rutherford
He did the Foil experiment -
1911 - Rutherford
He proposed that in the center of the atom was a tiny, extremely dense, positively charged part called the nucleus. -
1913 - Bohr
He proposed that the electrons move around the nucleus in certain paths, or enery levels
