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