Transcript History of the Atom White Board Presentation

History of the Atom
Notes
 Dalton
 Thomson
pg 88-89 Zumdahl
pg 91 Figure 4.3 Zumdahl
pg 97 & 98 LeMay
 Millikan
pg 98 LeMay
 Rutherford pg 100-101 LeMay Figure 3-16
pg 91 –93 Zumdahl
 Moseley
pg 104 LeMay
 Chadwick pg 94 Zumdahl
 Bohr
pg 287-288 Zumdahl Figure 10-17
pg 284 –287 Zumdahl
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
History of the Atom
White Board Presentations
John Dalton
English schoolteacher, 1766-1844
Problem w/ previous model: No
logical/scientific structure or rules
Atomic Theory Of Matter:
5 postulates (next slide)
Model:

Atomic Theory of Matter
1. Each element is composed of atoms
2. All atoms of a given element are identical
3. All atoms of different elements are different
(#2 and #3 often combined)
4. Atoms are neither created nor destroyed
5. Atoms combine to form compounds and a
given compound has the same relative
numbers and kinds of atoms
History of the Atom
White Board Presentations
JJ Thomson
English physicist, 1856-1940
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:
History of the Atom
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Robert Millikan
American physicist, 1869-1953
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)
History of the Atom
White Board Presentations
Ernest Rutherford
Scientist from New Zealand, 1871-1937
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
History of the Atom
White Board Presentations
Henry Moseley
English scientist, 1887-1915 (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)
History of the Atom
White Board Presentations
Sir James Chadwick
English physicist, 1891-1974
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)
History of the Atom
White Board Presentations
Niels Bohr
Danish physicist, 1885-1962
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)