Electrolysis & Aluminum Synthesis:Charles Martin Hall pictured below was an American chemist, who discovered an inexpensive method for the isolation of purealuminum 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 UnitedStates 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.
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 tubes 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 Helmholtzs 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. Goldsteins 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 comets tail. See the work of Hedenus for pictures and additional information. 
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.
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
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
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
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
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.
Were 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
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 hecomprehends quantum mechanics.
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, Rutherfords nuclear atom should have an extremely short lifetime. Bohr thought about this problem and knew of the emission spectrum of hydrogen. He quicklyFoiling the Nazis!! realized that the two problemshttp://crescentok.com/staff/jaskew/ISR/chemis were connected and after sometry/aquaregia.htm thought came up with the Bohr model of the atom. Bohrs model of the atom revolutionized atomic physics.
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?
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:
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!
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= Plancks 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 Bohrs 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: Bohrs model was so successful that he immediately received world-wide fame. Unfortunately, Bohrs model worked only for hydrogen. Thus the final atomic model was yet to be developed.
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?
Building a Bohr Atom…A Bohr Model• Draw a Bohr model of a sodium atom: 23 Na 111) Draw the nucleus, indicate #p and #n2) 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
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?
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!
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
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.
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”!
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
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.htmlHeisenberg & Pauli often communicated in secret about thesubtleties of the Uncertainty Principle and the Exclusion • This movie, “QuantumPrinciple. 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
Which one is Heisenberg?“The more precisely the position is determined, theless precisely the momentum is known in thisinstant, and vice versa.”--Heisenberg, uncertainty paper, 1927Check it out…interesting….http://www.aip.org/history/heisenberg/p08.htm 55
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.
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