GENERAL CHEMISTRY 1140
QUANTIZATION OF ELECTRONS
BOHR ATOM
- 1873 - MAXWELL - LIGHT IS AN ELECTROMAGNETIC WAVE
- 1900 - PLANCK - LIGHT IS QUANTIZED
- RADIATION FROM HOT BODIES
- 1905 - EINSTEIN - LIGHT IS A PARTICLE (PHOTON)
- PHOTOELECTRIC EFFECT
- 1885 - BALMER - ATOMIC SPECTRUM OF HYDROGEN
- BEING A MATHEMATICIAN, LOOKED FOR AN EQUATION
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- THE NUMBERS: n1 = 1, 2, 3, etc.; n2 = 2, 3, 4, 5, ETC., HAD NO PHYSICAL MEANING
PLUG TWO WHOLE NUMBERS IN AND YOU GET THE FREQUENCY OF AN OBSERVED WAVELENGTH!!.
WE NOW CALL THESE NUMBERS "QUANTUM NUMBERS".
- BOHR'S PLANETARY MODEL OF THE ATOM (1913)
- ELECTRONS ORBIT THE NUCLEUS
LIKE PLANETS ORBIT THE SUN
- ONLY CERTAIN ORBITS ARE ALLOWED (QUANTIZED!)
- BASED ON NEWTON'S LAWS OF MOTION AND ELECTROSTATICS
- UPON HEATING, ELECTRON GOES TO A HIGHER ENERGY ORBIT
- ELECTRON FALLS BACK TO LOWER ENERGY ORBIT AND EMITS ENERGY AS A PHOTON

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- EXCITATION-EMISSION SIMULATION
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- IF YOU SOLVE BOHR'S EQUATION FOR THE FREQUENCY, YOU GET BALMER'S EQUATION!
- BOHR'S ORBIT THEORY ALLOWED ONE TO PREDICT HYDROGEN SPECTRA QUITE WELL. BUT WHY WERE ONLY
CERTAIN ORBITS ALLOWED?
- DE BROGLIE (1924) SAID ELECTRONS BEHAVE AS STANDING WAVES
- THE WAVELENGTH IS RELATED TO QUANTUM NUMBER n AND THE RADIUS r
- AND FURTHER PROPOSED WAVELENGTH RELATED TO MASS, VELOCITY, AND PLANCK'S CONSTANT
- A FEW YEARS LATER IT WAS DEMONSTRATED THAT ELECTRONS ARE DIFFRACTED BY METAL FOILS
MUCH LIKE X-RAYS.
- LIGHT IS FOUND TO HAVE WAVE AND MATTER (PHOTON) PROPERTIES
- ELECTRONS ARE FOUND TO HAVE MATTER AND WAVE PROPERITES
- NEW PHYSICS!!
- NOTE: MANY OF THE NEW IDEAS CAME ON THE HEELS OF OTHER NEW IDEAS
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- A GREAT MODEL WITH A FEW PROBLEMS
- IT WORKS FOR H, He1+, Li2+, BUT VERY FEW OTHER SPECIES!
IT APPEARS TO ONLY DESCRIBE THE INTERACTION BETWEEN ONE ELECTRON AND A POSITIVE NUCLEUS
IT DOES NOT WORK FOR TWO OR MORE ELECTRONS!
- IT IMPLIES THAT WE KNOW THE "POSITION" OF A WAVE
- IT VIOLATES HEISENBERG'S UNCERTAINTY PRINCIPLE
HEISENBERG - IT IS IMPOSSIBLE TO KNOW SIMULTANEOUSLY BOTH THE MOMENTUM (p = m v) AND THE
POSITION OF A PARTICLE WITH CERTAINTY.
- HEISENBERG'S UNCERTAINTY PRINCIPLE (PARAPHRASED)
IF WE KNOW WHERE IT'S AT, WE DON'T KNOW WHERE IT IS GOING.
IF WE KNOW WHERE IT'S GOING, WE DON'T KNOW WHERE IT'S AT.
- BOHR'S MODEL SAYS WE KNOW BOTH - A VIOLATION
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- SCHRODINGER'S MODEL OF THE ATOM (1926)
- FORMULATED AN EQUATION WHICH DESCRIBES THE PARTICLE AND WAVE PROPERTIES OF AN ELECTRON
WAVE FUNCTION Y HAS NO PHYSICAL MEANING
BUT Y2 GIVES THE PROBABILITY OF FINDING AN
ELECTRON IN THE SPACE DEFINED
SOLVE Y2 FOR WHOLE UNIVERSE AND THE PROBABILITY OF
FINDING THE ELECTRON IS 1 (USELESS CALCULATION)
SOLVE Y2 SO THAT THE PROBABILITY OF FINDING THE ELECTRON
IS 0.9 (90%) AND CALL THIS VOLUME AN "ORBITAL".
TWO DEFINITIONS
AN ORBITAL IS A REGION IN SPACE WHERE THE PROBABILITY OF FINDING THE
ELECTRON IN QUESTION IS HIGH (90%)
AN ORBITAL IS A REGION IN SPACE WHERE THE ELECTRON WAVE DENSITY IS HIGH (90%)
- CAN BE SOLVED FOR THE H ATOM AND OTHER ONE ELECTRON IONS
- CAN'T BE SOLVED EXACTLY FOR 2+ ELECTRON SYSTEMS
- CAN BE SOLVED APPROXIMATELY FOR 2+ ELECTRON SYSTEMS
GIVES RESULTS CONSISTANT WITH OBSERVATIONS SO WE WILL USE IT!
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