Democritus proposed the first idea of the atom. Substances made up of invisible, indestructible particles.
John Dalton
1811
Proposed Atomic Theory
All matter is made up of tiny, indivisible atoms
Atoms of the same element are the same
Atoms of different elements are different
Atoms combine in whole number ratios to form compounds
Dalton's Model
Wilhelm Roentgen
1895
Discovered x-rays
This led to many discoveries in the Atomic Theory
JJ Thompson
1897
Discovered electron to determine the charge to mass ratio of the electron.
Cathode Ray Tube Experiment
Discovered negatively charged electrons
Plum Pudding Model
Ernest Rutherford
1911
Concluded the atom is empty space with a small positive nuclear core
Gold Foil Experiment
Nuclear Model
Niels Bohr
1913
Tried to answer question: Why arent electrons pulled into the nucleus?
Electrons travel in definite energy levels without radiating levels.
Electrons in each orbit have a certain amount of energy.
Energy increases as distance from nucleus increases.
Bohr's Model
de Broglie
1923
Hypothesis- If waves can behave like particles, then particles can behave like waves.
Electrons can act like waves
Heisenberg
1926
Heisenberg's Uncertainty Principle
It's impossible to know the position and velocity of an electron at the same time.
Electrons move to fast to track
Schrodinger
1927
Schrodinger's Wave Equation
Treated the electron like a wave
Developed an equation to find the electron in any given place around the nucleus
Solution to this equation was a quantum number
