3. Electrolysis & Aluminum Synthesis:
Charles Martin Hall pictured below was an American chemist, who discovered an inexpensive method for the isolation of pure
aluminum from its compounds. The same electrolytic process was discovered concurrently by the French chemist Paul L.T.
Heroult and is therefore known as the Hall-Heroult process. It became the basis for the aluminum industries both in the United
States and in Europe.
Hall was born in Thompson, Ohio, on December
6th 1863. He became interested in chemistry, and
more specifically in finding an inexpensive
method for producing aluminum. While an
undergraduate at Oberlin College. After his
graduation in 1885, Hall set up laboratory at
home and began work on the purification of
aluminum. He had the idea that if he could find a
non-aqueous solvent for aluminum oxide, he
could produce metallic aluminum by
electrolysis, using carbon electrodes. On Feb.
23, 1886, Hall found that molten cryolite, which
is the mineral sodium aluminum fluoride, was
the solvent he needed for the process; using the
cryolite and aluminum oxide and homemade
batteries, he produced his first small globules of
aluminum.
9. Eugen Goldstein
• In the mid-nineteenth century, Julius Plücker investigated the light emitted in discharge tubes (Crookes
tubes) and the influence of magnetic fields on the glow. Later, in 1869, Johann Wilhelm Hittorf studied
discharge tubes with energy rays extending from a negative electrode, the cathode. These rays produced
a fluorescence when they hit a tube's glass walls, and when interrupted by a solid object they cast a shadow.
• In the 1870s Goldstein undertook his own investigations of discharge tubes, and named the light emissions
studied by others kathodenstrahlen, or cathode rays. He discovered several important properties of cathode
rays, which contributed to their later identification as the first subatomic particle, the electron. He found that
cathode rays were emitted perpendicularly from a metal surface, and carried energy. He attempted to
measure their velocity by the Doppler shift of spectral lines in the glow emitted by Crookes tubes.
• In 1886, he discovered that tubes with a perforated cathode also emit a glow at the cathode end. Goldstein
concluded that in addition to the already-known cathode rays, later recognized as electrons moving from the
negatively-charged cathode toward the positively-charged anode, there is another ray that travels in the
opposite direction. Because these latter rays passed through the holes, or channels, in the cathode, Goldstein
called them Kanalstrahlen, or canal rays. They are composed of positive ions whose identity depends on the
residual gas inside the tube. It was another of Helmholtz's students, Wilhelm Wien, who later conducted
extensive studies of canal rays, and in time this work would become part of the basis for mass spectrometry.
• The anode ray with the smallest e/m ratio comes from hydrogen gas (H 2), and is made of H+ ions. In other
words this ray is made of protons. Goldstein's work with anode rays of H+ was apparently the first
observation of the proton, although strictly speaking it might be argued that it was Wien who measured the
e/m ratio of the proton and should be credited with its discovery.
• Goldstein also used discharge tubes to investigate comets. An object, such as a small ball of glass or iron,
placed in the path of cathode rays produces secondary emissions to the sides, flaring outwards in a manner
reminiscent of a comet's tail. See the work of Hedenus for pictures and additional information. [2]
20. Rutherford’s Model
• How did Rutherford’s Model improve
upon Thomson’s Model?
• What were the weaknesses with
Rutherford’s Model?
• Limitations of Classical Mechanics in
working with sub-atomic particles
• Success and limitations of Rutherford
model of an atom:
1. It showed for the first time, that the atomic
volume is mostly devoid of mass except at
its tiny positively charged center.
2. The classical theory predicts the
accelerating electron in orbit to radiate
electromagnetic energy. One would think,
the electron that radiates would decrease
its total energy and fall spiraling into the
nucleus collapsing the atom. Whereas we
know the atoms to be stable.
25. Toward a Quantum Model of the Atom
• Classical Physics, (Mechanics), and Rutherford’s nuclear model cannot
explain chemical properties of elements.
• Experiments with radiant energy, light, reveal interesting properties of
matter perhaps related to the atomic model.
• What is the “visible spectrum”? IR? UV? …line spectra? emission spectra?
• A cool web site:http://jersey.uoregon.edu/vlab/elements/Elements.html
27. Electromagnetic Spectrum
• Visible spectrum range
• Plank’s equation, E=hc/λ(lambda)
• h=6.626 x 10-34 J•s
• lambda=wavelength
• C=3.00 x 108 m/sec
• Practice Problem 3.24, pp 96
28. Electromagnetic Radiation:
Light…Energy?
• E=hc/λ
E = energy
h = Planck’s constant = 6.626 x 10-34
J•s
λ= wavelength
Q: What is wavelength?
c = 3.00 x 108 m/s
Questions:
1. What does this equation allow
you to do?
2. How are E and λ related?
Explain.
• c = λυ
• υ = frequency
Question:
1. What is frequency? Explain.
2. Practice Problem 4.3; pp 122
29. Will the Real Niels Bohr Please Stand Up?
• The Energy of Electrons is Quantized!
• Electrons may have only particular, discrete amounts of energy!
• Explain how these statements relate to the hydrogen spectrum shown
below!
• Hint: Why are there black gaps between the solid colored vertical lines
in the hydrogen spectrum? (There do not appear to be intermediate
amounts of energy!) In other words the spectrum in NOT continuous.
• Below you can see an emission line spectrum of hydrogen. It was
produced by exciting a glass discharge tube of hydrogen gas with about
5000 volts from a transformer. It was viewed through a diffraction
grating with 600 lines/mm. The colors cannot be expected to be accurate
because of differences in display devices
30. The 5th Solvay Conference: Brussels from
23-29 October 1927.
• Back row: A Piccard, E Henriot, P Ehrenfest, Ed Herzen, Th De Donder, E Schroedinger, E Verschaffelt, W Pauli, W
Heisenberg, R H Fowler, L Brillouin.
Middle Row: P Debye, M Knudsen, W L Bragg, H A Kramers, P A M Dirac, A H Compton, L de Broglie, M Born, N Bohr.
Front Row: I Langmuir, M Planck, Mme Curie, H A Lorentz, A Einstein, P Langevin, Ch E Guye, C T R Wilson, O W
Richardson.
31. We're Getting a New Deal for Physics!
• Classical Physics: Objects may have
any energy!
• Quantum Physics: Objects, e.g.,
electrons, may have only specific
energies
Hmmm….so let’s see, when the car
accelerates, it is accelerating in a
quantum manner, by set, specific
amounts of speed, not in a smooth
linear manner……uhh…isn’t that a
little “herky-jerky”?
http://www.nhra.com/video/default.aspx
32. Eureka!
• Classical Physics works for
objects you can see, like big
objects.
• Quantum Physics works to
describe the behavior of
objects too small to observe,
Tyler
Bean i.e., sub-atomic particles---
electrons!
Hey Bob, Toby looks so cute when he
comprehends quantum mechanics.
33. The Bohr Model: Background
In 1913 Niels Bohr came to
work in the laboratory of Ernst
Rutherford. A few years earlier
Rutherford discovered the nuclear
model of the atom. He asked Bohr
to work on this model since he
believed that there were some
problems with the model.
According to the physics of the
time, Rutherford's nuclear atom
should have an extremely short
lifetime. Bohr thought about this
problem and knew of the emission
spectrum of hydrogen. He quickly
Foiling the Nazis!! realized that the two problems
http://crescentok.com/staff/jaskew/ISR/chemis were connected and after some
try/aquaregia.htm thought came up with the Bohr
model of the atom. Bohr's model
of the atom revolutionized atomic
physics.
35. Hydrogen gas, Discharge Tube, Pink
Light…
• Why does the gas
“glow” pink when Mr.
Bean turns on the
generator?
• Why does the pink light
separate into distinctly
different colored lines in
a hydrogen line
spectrum?
• Do excited hydrogen
atoms emit energy?
light?
36. Emission of Light = Relaxation Energy
• An electron in an excited state can release energy in the form
of light that corresponds to visible wavelengths that we see in
the hydrogen line spectrum.
• This emitted energy is called “relaxation energy”.
• There are many relaxation energies that correspond to
wavelengths that are outside the visible spectrum:
37. Balmer et al:
1. The visible hydrogen spectral lines are in the 380nm-750nm range in
what is called the “Balmer” series.
2. Other energies are released for different transitions, e.g., n=5 to n=1, etc.
that correspond to wavelengths beyond the visible spectrum.
3. Given all the energy transition possibilities…this gets pretty
complicated. New image what this would be like for a multiple electron
atom!
40. The Bohr Model FOUR Principles:
1. Electrons assume only certain orbits around the nucleus. These orbits are stable and
called "stationary" orbits.
2. Each orbit has an energy associated with it. For example the orbit closest to the
nucleus has an energy E1, the next closest E2 and so on.
3. Light is emitted when an electron jumps from a higher orbit to a lower orbit and
absorbed when it jumps from a lower to higher orbit.
4. The energy and frequency of light emitted or absorbed is given by the difference
between the two orbit energies, e.g.,
E(light) = |Ef - Ei|
E(light) = hυ Note: υ = frequency; E = hc/λ; λ = hc/E; c = λυ
h= Planck's constant = 6.627x10-34 J•s
where "f" and "i" represent final and initial orbits and ΔE
With these conditions Bohr was able to explain the stability of atoms as well
as the emission spectrum of hydrogen. According to Bohr's model only certain
orbits were allowed which means only certain energies are possible. These energies
naturally lead to the explanation of the hydrogen atom spectrum:
Bohr's model was so successful that he immediately received world-wide
fame. Unfortunately, Bohr's model worked only for hydrogen. Thus the final atomic
model was yet to be developed.
41. Toward a Bohr or Quantum Model…
• Orbits, “shells”, get larger
as the principal quantum
number, (n), increases.
• Electrons in the n=1 orbit
have the lowest energy,
(ground state). Electrons in
orbits where n is larger have
more energy.
• Each shell can hold a
maximum of 2n2 electrons.
Hmmm…what are the
electron capacities for the
first four shells?
42. Building a Bohr Atom…A Bohr Model
• Draw a Bohr model of a
sodium atom: 23 Na
11
1) Draw the nucleus, indicate
#p and #n
2) Determine the #e-’s in the
atom.
3) Fill shells to their capacity
with e-’s starting with n=1,
(lowest energy, most
stable), to
43. The Mystery of Periodicity &
Line Spectra Explained!!!
• The number of electrons in the valence shell of an atom is
equal to the Roman numeral group for the representative
elements…Eureka! Uuh…what’s a “valence” shell?
44. Bohr: Periodicity
• Bohr model shows that atoms of elements in the
same groups, (families), of the representative
elements have identical electron configurations in
their valence shells!
• Hence…strong evidence to support a direct cause-
effect relationship between similar chemical
properties of elements in the same groups of
representative elements and their common valence
shell electron configurations!
45. Bohr: Line Spectra
• It explained why line spectra exist.
• Bohr’s mathematical model using Planck’s results
can reproduce the hydrogen line spectrum.
• Bohr’s mathematic model quantified the energies of
each line in the hydrogen spectrum.
• The differences in the energies between each shell
correspond to the equivalent energies associated with
each spectral line in the hydrogen line spectrum.
• http://www.youtube.com/watch?v=-YYBCNQnYNM&feature=related
48. No Model is Perfect!!!!
• Predicted Helium line spectrum did not match up
with observed helium line spectrum.
• Bohr’s mathematical model could not correctly
predict any spectrum beyond Hydrogen.
• Improved spectroscopes revealed that the Hydrogen
line spectrum was not so simple.
• What was thought to be single vertical lines in the
spectrum were in fact closely spaced compound lines
that appeared previously as single, bold spectral line.
50. And then there were Sub-Shells!
• The existence of multiple lines within
a single, bold spectral line was
explained by the existence of sub-
shells within a shell.
• Sub-shells are closely spaced in
energy and size.
• The principle quantum number
corresponds to the number of sub-
shells in each shell.
• Electron capacity for each sub-shell:
s=2
p=6
d = 10
f = 14
• s pdf in order of increasing
energy and size
• But then there is this “Potassium
Problem”!
53. Modern Quantum Mechanical Model of the
Atom
• Schröedinger: Wave Mechanics…
the idea that electrons have wave
like behavior
• Heisenberg: Uncertainty
Principle…the idea that you can
estimate the probable location of
an electron in an atom.
• Sub-shells correspond to probable
locations, (and energies), for
electrons.
• Sub-shells have shapes: orbitals:
s, p, d and f
54. MQMM
• The Modern Quantum
Mechanical Model:
• Retains Rutherford’s tiny,
massive, positive nucleus
• Retains Bohr’s idea of quantized
energy of electrons
• http://www.upscale.utoronto.ca/GeneralInterest/
Harrison/BohrModel/BohrModel.html
• http://www.upscale.utoronto.ca/GeneralInterest/
Harrison/BohrModel/Flash/BohrModel.html
Heisenberg & Pauli often communicated in secret about the
subtleties of the Uncertainty Principle and the Exclusion • This movie, “Quantum
Principle. It was important to keep everything “Top Secret” Mechanics”, is long, but well
worth it.
• http://www.youtube.com/watch?v=Nv1_Y
B1IedE&feature=BFa&list=LPWBNBv75
jtYM
55. Which one is Heisenberg?
“The more precisely the position is determined, the
less precisely the momentum is known in this
instant, and vice versa.”
--Heisenberg, uncertainty paper, 1927
Check it out…interesting….
http://www.aip.org/history/heisenberg/p08.htm
55
59. Electron Configurations Order of Filling (Easier):
• Write an expanded
electron configuration
for an atom of lead.
• Now, write the “noble
gas” shortcut
configuration for an
atom of lead.
An easier shortcut method for
filling sub-shells.
69. The Song of the Elements!
• Memorize this song. If Tom
you sing it in a school Lehrer…
assembly with a another
pianist and legend..
accompanied by our
class then…
• You win a $100 gift
certificate to Sushi
dinner in Quincy.
• http://www.youtube.com/watch?v=aPq
3SEteEJc
