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Chapter 3

CH-1010 Chapter Notes - Chapter 3: Joseph Von Fraunhofer, Johann Jakob Balmer, Fraunhofer Lines


Department
Chemistry
Course Code
CH-1010
Professor
Laura Lanni
Chapter
3

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Chapter 3
3.1 Waves of Light
Classical physics predict: negatively charged electrons orbiting a positively
charged nucleus lose energy and spiral into nucleus
oOpposites attract remember
Electromagnetic radiation: or radiant energy
oForm of light
oTo see the stability of atoms we need to study how atoms interact w/
this
oEx. Visible light
All forms of ratiations: electromagnetic
James Clark Maxwell theory
oElectromagnetic radiation moves through space as waves w/ 2
perpendicular components
An oscillating electric field and an oscillating magnetic field
Oscillate: move or swing back and forth at a regular speed
Wavelength () : distance from one wave crest to the next
oFrom left to right of spectrum: wavelengths get bigger
oFrom right to left of spectrum: wavelengths get smaller
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Frequency (): number of crests that pass a stationary point in space per
second
Hertz (Hz): equal to 1 wave per second
Speed of light (c):
o = c
othe value of c: 2.998 x 10^8
3.2 Atomic Spectra
Joseph Von Fraunhofer: Fraunhofer lines
oSet of dark lines in the otherwise continuous solar spectrum
Atomic Emission spectra: characteristic patterns of bright lines produced
when atoms are vaporized in high temp flames or electrical discharge
Atomic absorption spectra: atoms of elements in gas state absorb electro.
Radiation when illuminated by external source of radiation
3.3 Particles of light: quantum theory
Max Planck proposed another model to describe emission spectra of hot
objects
oPropose that objects emit electromagnet. Radiation only in integral
multiples
Quantom: elemententary unit for electromagnetic radiation emitted by
objects
oE= h
o: frequency of the radiation
oh: Plancks constant
6.626 x 10^-34
oE= hc/
Quantum theory: plancks model characterized by these
Quantized: values restricted to whole number multiples of a specific base
value
Photons: tiny packet of radiant energy
oRep. elementary building blocks of electromag. Radiation
Photoelectric effect: the release of electrons from a material as a result of
electromagnetic radiation striking it
oElectrons emitted from metals and semiconductor materials when
illuminated by/absorb electromagnetic radiation
oPhotoelectrons
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Threshold Frequency (): minimum frequency of light required to produce
photoelectric effect
oRadiaton less than threshold value: produce no photoelectron
No matter how intense radiation is
Einstein: used Plancks Quantum model
oHelp explain ability of the photoelectric materials to emit
photoelectrons
Every photoelectric material has a characteristic threshold
frequency assoc. w/ the minimum quantum of absorbed
energy needed to remove a single electron from the materials
surface
Threshold frequency= minimum absorbed energy needed to
remove single electron from surface
Work Function (): minimum energy needed to emit photoelectron from
photoelectric material
o
: strength of attraction b/w nuclei of metals atom and electrons
surrounding nuclei
Photoelectron emitted when radiant energy provides electron enough
energy to break from materials surface
oPhotons
Photons w/ frequency above (threshold frequency): enough energy to
dislodge elctron
oExtra energy in work function: kinetic energy
Higher frequency: greater kinetic energy of ejected electron
3.4 The Hydrogen Spectrum and the Bohr Model
Balmer Equation
o
oFormulated by Johann Balmer
Predict the wavelengths in nanometers
oM: integer greater than 2 (3,4,5,6)
Predict the wavelength of the 4 brightest hydrogen lines
oN: 2
Ex. M=3 solve for 
= 364.56 x 9/5
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