ATOMIC THEORY

DEMOCRITUS 400 BC

ATOMOS THEORY

• Indivisible
• He was the first person to think about the origin of matter
• He crushed up substances and determined that they couldnt be made any smaller

ARISTOTLE 350 BC

FOUR ELEMENTS

• They thought everything was made of earth, wind, fire and water
• They thought the elements were pure
• The four elements needed to be balanced

DALTON 1808

BILLIARD BALL

• Atoms are small
• Atoms of different elements have different masses
• Atoms are solid

J J THOMSON 1904

PLUM PUDDING MODEL

• Atoms have electrons
• Things around the electrons are a positive soup
• Positives and negatives needed to balance

RUTHERFORD 1911

GOLD FOIL EXPERIMENT

• Each atom had a small positive charge
• He came up with the word atomic mass
• He calculated the charge

MILLIKAN 1913

OIL DROP

• He determined what the charge was for electrons
• The electron charge was the same value for all different forms of electricity
• The mass of an electron is at least 1000 times smaller then the lightest atom

CHADWICK 1932

DISCOVERY OF THE NEUTRON

• He proved the existence of neutrons
• They have no electrical charge
• Mass of the neutron is equal to 0.1 percent more then the mass of the proton