ATOMIC THEORY

DEMOCRITUS

ATOMOS

• First person to come up with the concept of an atom
• Learned a piece of matter was divisible into smaller parts
• Called individual parts "atoma" where we get word "atom"

ARISTOTLE

EARTH WIND FIRE WATER ELEMENTS

• Believed that matter is a mixture of four natural elements
• Thought all four elements are made up of four properties
• Four properties: clod, hot, wet and dry
• This theory was proven incorrect

JOHN DALTON

BILLIARD BALL MODEL

• Discovered that atoms are the smallest particle of an element
• That atoms of different elements have different masses
• Atoms are solid, indestructible units much like a billiard ball

JJ THOMSON

PLUM PUDDING MODEL

• Discovered that the atom is mostly empty space
• This means its neutral
• Figured out electrons are floating around the empty space

ROBERT MILLIKAN

MASS AND CHARGE OF AN ELECTRON

• Also called Oil Drop Experiment
• Measured the gravitational force of charged oil drops
• Could then figure out that there was a charge of an electron
• Was awarded the Nobel prize for his physics

ERNEST RUTHERFORD

THE GOLD FOIL MODEL

• Rutherford shot a beam at gold foil
• Noticed some particles scattered
• Realized there is a nucleus
• A small, dense concentration of charge and mass

SIR JAMES CHADWICK

PROTON AND NEUTRON MODEL

• Discovered the particle in the nucleus of an atom
• Became known as the neutron because it has no electric charge
• He measured how hard an atom recoiled after a collision
• He was able to estimate the mass of the nucleus
• They knew how many protons and electrons existed so they found neutrons