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400 BCE
Democritus
Democritus adopted the atomic theory from his mentor, Leucippus. He said that everything was made of atoms. He also said the atoms were indivisible. To test this theory, he took a seashell and broke it in half. He then took one of those halves and broke it, too. He continued this until he was left with a piece so small that he couldn't broke it anymore. He believed that was the atom. -
John Dalton
John Dalton's atomic theory stated that all elements were made of atoms. All atoms of the same element are identical. Atoms of different elements are different. He also said that atoms are indivisible and indestructible. He also concluded that some elements are made of multiple atoms and are called compounds and that they must be in whole number ratios. -
J.J. Thompson
J.J. Thompson discovered the electron and its negative charge. He used gas discharge tubes and noticed movement called cathode rays. The rays were moving from the negative end of the tube to the positive end. He then concluded that the rays were actually particle that were repelling the negative end and he called them "electrons." -
Ernest Rutherford
Ernest Rutherford discovered the nucleus of atoms. He did this by shooting alpha particles at a gold foil. He expected the particle to go straight through and most of them did. Some of them directly deflected or slightly bounced away. He used this information to conclude that the alpha particles either bounced directly off of the nucleus or were repelled by its positive field. -
Niels Bohr
Niels Bohr composed a model of te atom which was very similar to one of the solar system. The electrons orbited around the nucleus on different levels. He said that each level had a different electron capacity and that electrons on different levels had different energy levels. -
Schrodinger and Heisenberg
Schrodinger used a microscope to measure the momentum of electrons. Heisenberg implemented quantum mechanics to interpret the behavior of atoms.
