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450 BCE
Democritus
Democritus wondered what would happen if you cut matter into smaller and smaller pieces. To prove this, he continued to cut an apple until he couldn't anymore. Democritus thought that you eventually couldn't cut it any smaller, and he called that smallest piece the "atomos", which today means "atom". -
Dalton
Dalton revived Democritus' ideas. He developed one of the most important theories in science. Dalton studied the pressure of gasses and concluded that gases must consist of tiny particles in constant motion. When discovering this, he performed a series of different experiments including mixing lots of different gases together. -
Bohr
Bohr had worked with Rutherford, but focused more on the electrons. Bohr measured the energy gained when electrons absorb energy and move to a higher level. He discovered that if the atom changes, so does the electron energy. -
Thomson
Thomson discovered electrons. He did experiments in which he passed an electric current through a vacuum tube. Thomson also developed a plum pudding model that shows the atom as a sphere of positive charge with negative electrons scattered all through it. -
Rutherford
Rutherford found the nucleus, and later discovered protons. He thought that electrons randomly orbit around the nucleus. Rutherford used alpha particles to study atoms. During this experiment, he aimed a beam at a very thin sheet of gold foil. Outside of the foil he placed a screen of material that flowed when the alpha particles struck it.
