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492 BCE
Democritus
He asked himself what happened if you cut matter into small pieces, and then into even smaller pieces. Eventually there was nothing left to be cut. He called these "uncuttable" pieces "atomus". Now known as atoms. -
Dalton
Constructed many experiments that provided evidence for atoms. He said that gases contained tiny particles that never stopped moving. People didn't believe him so he made a theory. 1) All substances are made of atoms. They can't be cut into smaller particles. They can't be created or destroyed. 2) All atoms of the same element have the same mass. Different elements have different masses. 3) Atoms join together to form a compound. A compound is always made of the same atoms in the ratio. -
Thomson
Discovered the first subatomic particle : the electron. He found out that there was something surround the atom. It gave a negative charge. There was currents of electricity in the cathode ray tube, so that got him thinking. -
Rutherford
Physicist from New Zealand. He found the nucleus! He discovered that the other subatomic particles were located here (protons and neutrons). In 1932, one of his students discovered the neutrons. -
Bohr
He proposed the theory that the electrons orbited the nucleus like the planets orbited the sun. This theory was called Planck's Quantum Theory. He believed that the electrons were located in energy groups.
