ATOMIC THEORY TIMELIME

DEMOCRITUS (400 BC)

ARISTOTLE (384-322 BC)

• Believed in the four elements
• Thought that no matter how many times you cut a piece of matter
• In half you will always have a smaller piece of matter

ANTOINE LAVOISIER (1734-1794)

JOHN DALTON (1776-1844)

• Created the Law of Multiple Proportions
• Led directly to the proposal of the Atomic Theory

J. J. THOMSON (1856-1940)

• Discovered the negatively charged electron
• Proposed the "plum pudding" model for an atom

ERNEST RUTHERFORD (1871-1937)

• Proposed that all of the mass and positive charge was at the center of the atom
• Used the gold foil experiment in 1911
• Also proposed the existence of the neutron

MAX PLANCK (1858-1947)

NIELS BOHR (1885-1962)

• Proposed that electrons travel in an orbit around the nucleus
• There are different energy levels
• The more energy the electron has, the further away it is from the nucleus
• Electrons in an excited state jump levels
• Electrons in a relaxed state move towards the nucleus

ERWIN SCHRÖDINGER (1887-1961)

• Found an equation that predicts the probability of finding an electron in an exact place