1. History of the Atom Notes
Dalton pg Zumdahl
Thomson pg 91 Figure 4.3 Zumdahl
pg 97 & 98 LeMay
Millikan pg 98 LeMay
Rutherford pg LeMay Figure 3-16
pg 91 –93 Zumdahl
Moseley pg 104 LeMay
Chadwick pg 94 Zumdahl
Bohr pg Zumdahl Figure 10-17
pg 284 –287 Zumdahl

2. History of the Atom White Board Presentations
Democritus (example)
Greek philosopher, around 400 BCE
Problem with previous model: no system or explanation, just “magic”
Model: 
“atomos” compose the world- tiny, indivisible particles that retain the chemical identity of the element

4. History of the Atom White Board Presentations
John Dalton
English schoolteacher,
Problem w/ previous model: No logical/scientific structure or rules
Atomic Theory Of Matter:
5 postulates (next slide)
Model: 

5. Atomic Theory of Matter
Each element is composed of atoms
All atoms of a given element are identical
All atoms of different elements are different (#2 and #3 often combined)
Atoms are neither created nor destroyed
Atoms combine to form compounds and a given compound has the same relative numbers and kinds of atoms

7. History of the Atom White Board Presentations
JJ Thomson
English physicist,
Problem w/ previous model: no subatomic particles
Experimental Evidence: cathode ray tube experiment where particles smaller than atoms are shown to have negative charge (electrons) with a small mass
to charge ratio
Model: Plum Pudding Model:

9. History of the Atom White Board Presentations
Robert Millikan
American physicist,
Problem w/ previous model: no known amount of charge of an electron
Experimental evidence: oil drop experiment where (-) charged oil drops pass between (+) plates and rate of fall is measured. All were multiples of 1.60 x 10-19C (one e-).
He also calculated the mass of an e- based on the charge and the known mass:charge ratio.
Model: (looks the same as Thomson’s)

11. History of the Atom White Board Presentations
Ernest Rutherford
Scientist from New Zealand,
Problem w/ previous model: does not account for  particles bouncing back
Experimental evidence: gold foil experiment where he shot (+) charged  particles at very thin gold foil and saw evidence for
a very small, dense, positively
charged core to the atom.
Model: Nuclear atom

13. History of the Atom White Board Presentations
Henry Moseley
English scientist, (Rutherford’s student)
Problem w/ previous model: does not account for elemental differences
Experimental evidence: X-Ray diffraction patterns of metals showed that each element has a unique positive charge in the nucleus that determines the atoms identity (atomic number)
Model: (looks the same as Rutherford’s)

15. History of the Atom White Board Presentations
Sir James Chadwick
English physicist,
Problem w/ previous model: mass of protons did not account for mass of nucleus and a nucleus of all protons (+) would repel and fall apart
Experimental evidence: He bombarded metals (beryllium) with  particles, causing a radiation that was both neutral and a mass similar to a proton
Model: (looks the same as Rutherford's, but with neutrons in the nucleus as well)

17. History of the Atom White Board Presentations
Niels Bohr
Danish physicist,
Problem w/ previous model: did not account for specific energy levels of e- seen in the light spectrum analysis
Experimental evidence: The energy spectrum of hydrogen shows discrete “quanta” of energy involved in e- configurations
Model: (Bohr model)