1. The Atomic Model
Chem 9

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 proposed
first 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 1887
by using a cathode ray tube
initially called electrons CORPUSLES

5. Robert A. Millikan (1868 – 1953)
1900 – mass of Electron approximately 1/2000 the mass of a Hydrogen atom
1916 -determined the charge carried by an electron
Millikan OIL DROP EXPERIMENT

6. Eugene Goldstein ( )
1866 Eugene Goldstein found Positive particle – Protons
He named them CANAL RAYS

7. Sir James Chadwick
Discovered
the neutron in 1932
Has no charge
Neutron’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 and
negative electrons are scattered around
the 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 based
on how much energy it has.
-Atomic orbitals (s,p,d,f) are NOT fixed paths as Bohr suggested

12. Summary Dalton : Solid Sphere Thomson : Pos. & neg mixed together
Rutherford: Positive nucleus, neg electrons surrounding it
Bohr: Positive nucleus, neg electrons in exact orbits
Quantum Mechanical Theory
(Electron cloud theory)