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400 BCE
Democritus
Democritus contribution to the Atomic Theory was his beliefs that atoms were indivisible and indestructible. -
John Dalton
John Dalton was English chemist and teacher. His contributions to the Atomic Theory included making an actual theory out of Democritus's beliefs. He made the following statements: 1. All atoms are made of atoms 2. Atoms of the same element are identical 3. Atoms of different elements can physically mix or chemically combine 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Elements never change into other elements. -
Eugen Goldstein
Eugen Goldstein was an English physicist who is sometimes credited with discovering the proton. He also theorized that every atom must be equal in the atom of negatively and positively charged particles. He utilized the cathode-ray tube. -
JJ Thomson
JJ Thomson was an English physicist who discovered the electron through use of the cathode-ray tube experiment. -
Cathode Ray Tube Experiment
JJ Thomson created the cathode-ray tube experiment. In the experiment, gases were sealed in glass tubes fitted at both ends with electrodes, one positive and one negative, which created a cathode ray. This allowed him to conclude electrons are part of all elements. -
Ernest Rutherford
Ernest Rutherford was a student of English physicist, JJ Thomson. Rutherford proposed the atom is mostly empty space and that electrons move around the nucleus. -
Gold-Foil Experiment
To prove his theory, Rutherford made the gold-foil experiment. In this experiment, he aimed a beam of the alpha particles at a piece of gold foil. Little to no refraction occured, which meant atoms were mostly empty space -
Niels Bohr
Niels Bohr was a Danish physicist and a student of Rutherford. He discovered that electrons are found on energy levels that follow certain paths like the planets in the solar system. He also came up with a model we still use today to represent the atom. -
Louis De Broglie
Louis De Broglie was a French physicist who discovered the moving particles have properties of waves, and from that he developed wave mechanics theory which is the basis for quantum physics. -
Erwin Schrodinger
Erwin Schrodinger was an Austrian Physicist who came up with the quantum mechanical model of the atom. This theorized that electrons didn't move in set paths, but in waves. This introduced the concept of sub-energy levels. -
James Chadwick
James Chadwick was an English physicist credited with the discovery of the neutron. He discovered the neutron when he shot alpha particles into beryllium atoms and an unknown radiation with a neutral charge occured.
