DEMOCRITIS 460 BC

ATOMIC THEORY

• All matter consists of invisible particles called atoms
• Atoms are indestructible
• Atoms are solid but invisible
• Atoms are homogenous

ARISTOTLE 450 BC

ARISTOTLES EARTH WIND FIRE AND WATER

• Four elements that everything was made of
• Earth, Wind, Fire, Water.
• Added a fifth element named aether, stars were made of it.

DALTON

BILLIARD BALL MODEL

• Atoms are the smallest particle of an element
• Atoms of different elements have different masses
• Atoms are solid and indestructible much like a billiard ball

THOMSON 1904

PLUM PUDDING MODEL

• Atom is composed of electrons
• Surrounded by positively charged "soup" to balance electrons
• Electrons positioned throughout the atom

RUTHERFORD 1911

POSITIVELY CHARGED NUCLEUS

• "Gold foil experiment" showed a positively charged nucleus
• All mass is concentrated in the nucleus
• Electrons circulate Around the atom

MILLIKAN 1908-19011

OIL DRIP

• Measured the charge of an electron
• Oil drip apparatus, measured mass of an electron
• The mass of an electron is at least a 1000 times smaller than the lightest atom

CHADWICK 1932

NUETRONS

• Believed particles with no charge could be in the nucleus
• Discovered neutron in atoms from gamma ray experiments
• Drew conclusion of neutral particles called neutrons were in the nucleus with the same mass as protons