ATOMIC THEORY

DEMOCRITUS

• Ancient Greek philosopher
• First person to propose the idea of the atom
• Said that atoms are indestructible
• He believed an atom was just a sphere
• "Nothing exists except atoms and empty space; everything else is opinion"

DEMOCRITUS' ATOMIC MODEL

JOHN DALTON

• Born September 6, 1766
• From Cumberland, England
• His atomic theory said that elements consist of small particles called atoms
• Said that atoms combine in simple whole number ratios to form molecules of compounds
• Dalton was able to determine the relative masses of the atoms

DALTON'S ATOMIC MODEL

J.J. THOMSON

• From Manchester, England
• Discovered the electron through the use of cathode rays
• Atomic model known as the "plum pudding" model
• States that atoms are breakable
• States that the atom's structure has electrons suspended in a posotively charged electric field

THOMSON'S EXPERIMENT

THOMSON'S ATOMIC MODEL

ERNST RUTHERFORD

• From Nelson, New Zealand
• Discovered the nucleus
• discovered that the nucleus has most of the mass of the atom
• the nucleus takes up 1/10 trillionth of the volume of an atom
• Said the nucleus was positively charged

RUTHERFORD'S EXPERIMENT

RUTHERFORD'S ATOMIC MODEL

NIELS BOHR

• From Copenhagen, Denmark
• Developed the modern atomic theory
• discovered that electrons travel in separate orbits
• Discovered that the nucleus contains neutral particles called neutrons

BOHR'S ATOMIC MODEL