Discovery of the Electron, Models & Theories

1. Discovery of the Electron, Models & Theories Jeffrey Thorin Daniel

2. JJ Thompson Robert Millikan • Found the accurate way to decide the charge carried with an atom • Discovered the electron • Wrote books on atomic theory and structure • First to suggest that atoms have parts

3. Niels Bohr Louis de Broglie • Looked into Bohr’s investigation and thought electrons moved in waves rather that circular orbits • Helped create a picture of the atomic structure(Bohr model) • This said that electrons orbit the nucleus in fixed circular orbits

4. Werner Heisenberg Erwin Schrodinger • Known for his theory in quantum mechanics • Proved Bohr’s theory wrong about the movement of electrons • Said we can’t  assign to an electron a position in space at a given time, nor follow it in its orbit • Developed a wave-equation that accurately gave energy levels to atoms

5. Bohr Model • An atom consisting of small positively charged nucleus orbited by negatively charged electrons • Similar to planetary model where planets orbit the Sun • Solar system uses gravitational forces whereas an atom uses electrostatic forces • Electrons have certain orbits with certain radii • Orbits are circular according to quantized energy levels • Orbits with larger radii have larger energies

6. Quantum Model • Based on quantum theory, which says matter also has properties associated with waves • Impossible to know the exact position and momentum of an electron at the same time • Uses complex shapes of orbitals (electron clouds)volumes of space in which there is likely to be an electron • Based on probability rather than certainty

7. Experiments • Thompson experimented with cathode rays and magnets that led to the discovery of the electron • Millikan devised an oil-drop experiment where he’d drop tiny charged droplets to find out their specific charge • Bohr based his model on experiments done by Ernest Rutherford; he saw Rutherford’s model wasn’t quite right and changed it • Broglie saw that Bohr’s model, specifically the electrons, move in waves, not in a circular orbit • Heisenberg also went off of Bohr’s model and elaborated more into quantum mechanics to explain the wave motion of electrons instead of a circular orbit • Schrodinger used mathematical equations to predict the likelihood of finding the electron and eventually found one that worked

8. Time Line of History • Scientists from the early 1900s • Theories developed without use of more precise modern technology Quantum Model

9. Over time… • Bohr’s model had a lot of problems and inaccuracies to it • Quantum model is considered “standard” and is also considered the most accurate physical theory ever created