ATOMIC THEORY TIMELINE

DEMOCRITUS 400 BC

ATOMOS THEORY

• Believed that matter could get down to a single atom.
• Most people did not believe him
• Came up with the idea of the atom

ARISTOTLE 384-322 BCE

4 ELEMENT THEORY

• Threw out the atomod theory
• Thought that all materials on earth were made of:
• Earth, fire, water, and air
• Changed democritus' idea
• Mislead the idea of atoms fore the next 2000 years

JOHN DALTON 1803

BILLIARD BALL THEORY

• Believed that all atoms were the same size and shape
• Also believed that there was different atom types
• Thought that all atoms were hard like billiard balls

JJ THOMSON 1897

PLUM PUDDING THEORY

• He discovered the electron
• He did so through his cathode ray experiment
• Electrons were small and negatively charged

ERNEST RUTHERFORD 1911

POSITIVELY CHARGED NUCLEUS

• Put the atom model in prospect and made it into a planetary model
• Put electrons on the outside
• Found his theory through the gold foil expermient

MILLIKAN 1909

MASS AND CHARGE OF AN ELECTRON

• Determined the mass and charge of an electron
• Did so through his oil drop experiment
• Determined that electrons are negatively charged
• He did not develop a model of an atom

CHADWICK 1932

PROTON AND NEUTRON THEORY

• Proved the existence of protons and neutrons
• His model is one that we use today
• He established that atomic number is determined by the number of protons in an atom