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430 BCE
Leucippus and Democratis
They first came up with the idea that matter is made up of tiny particles. They believed that is you cut something in half enough times, you'd have a particle that can't be cut anymore. They called this "A Tomos." -
Antoine Lavoisier
He proposed the law of conservation of mass which states that if matter changes shape or form, its mass will stay the same. It changed the understanding of the atom by showing that all mass cannot be created or destroyed. -
James Dalton
He determined that elements exist as individual packets of matter. This changed the understanding of the atom by showing that atoms are individual particles that make up elements. -
Discharge Tubes
Scientists started using discharge tubes which are gas filled tubes with electrodes at each end that admits light when an electrical current pass through them. This helped the understanding of the atom by showing that atoms have charges and are forms of energy. -
Goldstein
He learned that the tubes had positive charges as well as negative charges. This helped the understanding of atoms by revealing that they had both positive and negative charges. -
Joseph John Thompson
He measured how much heat the cathode rays generated, how much they could be bent by magnets, and other things. He proved that the cathode rays weren't rays or waves at all, but that they were very small negatively charged particles that we call electrons. -
Quantum Theory
This proposes that electrons weren't particles or waves. Instead they had properties of both and neither. The arrangement of the electrons around the nucleus could only be described in terms of probability -
Earnest Rutherford
He created an experiment using a thin sheet of gold foil and a screen coated with zinc sulfide. He bombarded the foil with alpha particles. After his experiment, he came to the conclusion that atoms had a nucleus. -
Niels Henrik David Bohr
He went to go study with Rutherford and created the Bohr model which showed the electrons in orbit around the nucleus in an atom. This gave us an idea of what an atom looks like. -
Werner Karl Heisenberg
He discovered that it is impossible to know with certainty both the momentum of an electron or any subatomic particle and its exact position.
