ATOMIC THEORY TIMELINE

DEMOCRITUS, 460 BC

ATOMOS MODEL

• Atomos - Greek for "uncuttable"
• A solid, round ball
• First theorized matter is made of small particles
• Very few believed him

ARISTOTLE, 384 BC

FOUR ELEMENTS MODEL

• Earth was everything dry
• Wind was everything wet
• Fire was everything hot
• Water was everything cold
• Combined, they made other elements

DALTON, 1803

BILLIARD BALL MODEL

• A round ball (billiard ball)
• "Atoms are indivisible & indestructible."
• "Compounds are formed by 2 or more atoms."
• Used Democritus' theory for his discovery

THOMSON, 1897

PLUM PUDDING MODEL

• Atoms consist of two charges
• Positively charged particle
• Negatively charged electrons
• Discovered through Cathode Ray Experiment

RUTHERFORD, 1909

POSITIVELY CHARGED NUCLEUS

• Positive charge is nucleus in the center
• Nucleus is the largest particle
• Electrons revolve around the nucleus
• Electrons follow an elliptical pattern
• Discovered through Gold Foil Experiment

MILLIKAN, 1909

MASS + CHARGE OF ELECTRONS

• Electron charge is 1.6x10^-19 Coulombs
• Electron mass is 9.1x10^-31 Kg
• Conducted the Oil Drop Experiment

CHADWICK, 1932

PROTON/NEUTRON MODEL

• Atomic # is determined by # of protons
• Discovered the neutron
• Found by shooting alpha rays at Be