2 The Greek Model Democritus - A Greek Philosopher, 400 BC. Concluded that matter could not be divided into smaller and smaller pieces forever.Eventually, the smallest piece of matter would be found.He used the word "Atomos“ meaning indivisible.
3 The Dalton Model: Billiard Ball Model John Dalton - The English chemist that proposedfirst Atomic Theory in 1803.All elements are composed of indivisible particles.Atoms of the same element are exactly alike.Atoms of different elements are different.Compounds are formed by joining atoms of two or more elements
4 The Thomson Model: Chocolate Chip Cookie Model Plum Pudding Model J. J. Thomson 1856 – 1940 – (English scientist)discovered negative particle (an Electron) in 1887by using a cathode ray tubeinitially called electrons CORPUSLES
5 Robert A. Millikan (1868 – 1953)1900 – mass of Electron approximately 1/2000 the mass of a Hydrogen atom1916 -determined the charge carried by an electronMillikan OIL DROP EXPERIMENT
6 Eugene Goldstein ( )1866 Eugene Goldstein found Positive particle – ProtonsHe named them CANAL RAYS
7 Sir James ChadwickDiscoveredthe neutron in 1932Has no chargeNeutron’s mass is close to proton’s mass
8 Ernest Rutherford - British Physicist Gold Foil Experiment In 1908, proved the atom had a small,dense, positively charged Nucleus.He said an atom is mostly empty space andnegative electrons are scattered aroundthe outside edge.
9 Niels Bohr (Danish scientist) The Planetary Model - 1913 Bohr proposed:Electrons move in definite orbits around the nucleus, like planets moving around the sun.That each electron moves in a specific energy level.
10 Quantum Mechanical Model Erwin Schrodinger ( )-Electrons have NO definite path in an atom.-Only a probable location is known basedon how much energy it has.-Atomic orbitals (s,p,d,f) are NOT fixed paths as Bohr suggested