ScientistsThe atom

Democritus

- 400 BC- Greek philosopher - No experimenting -Matter made up of indivisible particles = “atomos”

Dalton

1801: Thomas Jefferson President1802: John Dalton experimented and

concluded….1806: Fall of Roman Empire

1. Matter made up small particles= atomsCant be created, destroyed, or made smaller

2. Atoms of same element are identical Different elements = different atoms

3. Chem. Rxn atoms separate, join, or rearrange

4. Atoms of different elements can combine in whole number ratios: compounds.

Dalton

1850’s- Steam

• Steam powered engines of ships, trains, & factories

• Key Question’s of 19th Century= • “How to build more effective steam engines”

and • “ How to predict behavior of steam at high

temps and pressures.”

1896- Uranium

- Uranium was found to emit strange energy: - Radioactivity: warm to the touch - Can unlock secrets to the atom

1898- Marie Curie

Concluded Uranium atom gave off radiation ( but another chemist discovered first)Found Radium – led to cancer fighting drugsWon two Nobel Peace PrizesFound Polonium Kept radioactive materials in her pocketDied of leukemia from radioactive materials

1904-J.J. Thomson

• Plum Pudding Model/ Chocolate Chip Cookie• Discovered electrons ( 1897)• Experiment with cathode ray tube– Particles move toward positive end– Particles must be negatively charged– Disproved that the atom was indivisible (could be broken into parts)

Thomson versus Rutherford

Rutherford’s Goldfoil Experiment

Result: majority passed straight through some bounced @ large angles & straight back

1911-Rutherford

• Discovered: – atom was mostly empty space – Atom had a dense positively charged center

• Disproved the Plum Pudding Model – (he was a grad student of Thomson)

1913-Bohr

• Planetary model of atom• Electrons move in an orbit• Each orbit had a definite energy

1914- 1918: World War I

1926- Schrodinger

• Extension of Bohr’s model• The electron “cloud” shows where the electron is

most likely to be – You have a 90% chance of finding the electron

• Electrons move like waves

Quantum Mechanical Model

Dalton 1802Thompson 1904- “plum pudding”

Rutherford 1911

Bohr 1913 “planetary model” Quantum mechanical model

History of Atomic Models

1927- Heisenberg

Uncertainty Principle Can not know the speed and the location of

the e- at the same time

1932-Chadwick

• Prisoner of war in WW1• Worked for Rutherford • Discovered neutron • Issue: mass of helium was 4 but it only had 2

protons

Summary Video