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Chapter 2.1-2.4

CHEM 130 Chapter Notes - Chapter 2.1-2.4: Emission Spectrum, Bohr Model, Continuous Spectrum

Course Code
CHEM 130
Jadwiga Sipowska

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Lecture 5: 2.1-2.4
2-1 EM radiation
EM radiation = one of the ways that E travels through space
Waves have 3 primary characteristics: wavelength, frequency, speed
Wavelength (λ) – distance btw 2 consecutive peaks/troughs in wave
Frequency (v) number of waves (cycles) per second that pass a given point in space
Short λ higher ν
λ = meters, v = cycles per second, c = speed of light (2.9979*108 m/s)
v = hertz (1 cycle per second)
2-2: The nature of matter
o Planck’s constant energy can be gained or lost only in whole number multiples of the quantity hv
(h = constant)   
v = frequency of EM radiation
E can occur only in discrete units of size hv each individual one of these energy “packets” =
Quantum (of energy) minimum amount of energy that can be lost/gained by an
o E = hv energy of a quantum of radiation = Planck’s constant * frequency
o Planck’s constant = 6.626 * 10^-34 Js
Photon particle of EM radiation having 0 mass and carrying a quantum of energy
o E (of a photon) = hv
Min energy corresponds to the minimum frequency required to eject
the electron from the metal
System can transfer E only in whole quanta
o Einstein challenged theory that light moved only in waves and that it moved in particles proposed
that EM radiation is itself quantized said EM radiation can be viewed as stream of “particles”
(called photon)
   
Photoelectric effect the emission of electron from a metal when light shines on the metal
When v varies no electrons emitted by given metal below specific threshold frequency
Light w/ v lower than v0 no electrons are emitted, regardless of light’s intensity
Light w/ v > v0 # of electrons emitted increases w/ intensity of light
Light w/ v > v0 KE of emitted electrons increases linearly w/ v of light
o v0 = represents minimum E required to remove electron from metal’s surface
E0 = hv0
E0 (v < v0) can’t remove electron and light with this v can’t produce electron
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