Discovery of the Electron, Models &

Theories

JeffreyThorinDaniel

JJ Thompson• Discovered the

electron• Wrote books on

atomic theory and structure

• First to suggest that atoms have parts

Robert Millikan• Found the accurate

way to decide the charge carried with an atom

Niels Bohr Louis de Broglie

• Helped create a picture of the atomic structure(Bohr model)

• This said that electrons orbit the nucleus in fixed circular orbits

• Looked into Bohr’s investigation and thought electrons moved in waves rather that circular orbits

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

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

Quantum ModelBased 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 timeUses complex shapes of orbitals (electron

clouds) volumes of space in which there is likely to be an electron

Based on probability rather than certainty

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

Time Line of HistoryScientists from the early 1900sTheories developed without use of more precise

modern technology

Quantum Model

Over time…Bohr’s model had a lot of problems and

inaccuracies to itQuantum model is considered “standard” and is

also considered the most accurate physical theory ever created