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Scientists. The atom. Democritus . - 400 BC- Greek philosopher - No experimenting Matter made up of indivisible particles = “ atomos ”. Dalton. 1801: Thomas Jefferson President 1802: John Dalton experimented and concluded…. 1806: Fall of Roman Empire . Dalton.

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scientists

Scientists

The atom

democritus
Democritus

- 400 BC- Greek philosopher

- No experimenting

  • Matter made up of indivisible particles =

“atomos”

dalton
Dalton

1801: Thomas Jefferson President

1802: John Dalton experimented and concluded….

1806: Fall of Roman Empire

slide4
Dalton

1. Matter made up small particles= atoms

  • Cant 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.

1850 s steam
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
1896- Uranium

- Uranium was found to emit strange energy:

- Radioactivity: warm to the touch

- Can unlock secrets to the atom

1898 marie curie
1898- Marie Curie

Concluded Uranium atom gave off radiation

( but another chemist discovered first)

Found Radium – led to cancer fighting drugs

Won two Nobel Peace Prizes

Found Polonium

Kept radioactive materials in her pocket

Died of leukemia from radioactive materials

1904 j j thomson
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)

rutherford s goldfoil experiment
Rutherford’s Goldfoil Experiment

Result:

majority passed straight through

some bounced @ large angles & straight back

1911 rutherford
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
1913-Bohr
  • Planetary model of atom
  • Electrons move in

an orbit

  • Each orbit had a

definite energy

1926 schrodinger
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
history of atomic models
History of Atomic Models

Dalton 1802

Thompson 1904- “plum pudding”

Rutherford 1911

Bohr 1913

“planetary model”

Quantum mechanical model

1927 heisenberg
1927- Heisenberg

Uncertainty Principle

Can not know the speed and the location of the e- at the same time

1932 chadwick
1932-Chadwick
  • Prisoner of war in WW1
  • Worked for Rutherford
  • Discovered neutron
  • Issue: mass of helium was 4 but it only had 2 protons
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