CHEM 1201 Lecture Notes - Lecture 13: Photon, Johann Jakob Balmer, Louis De BrogliePremium
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Chem 1201 - Lecture 13 - Chapter 6: Electronic Structure of Atoms
The Wave Nature of Light:
● In 1801, the Young Double slit experiment demonstrated the “wave nature” of light.
When light is passed through two slits (S1 & S2) an interfrence pattern is observed on
the detector (photographis film, F). What observed were crests of waves at certain
points. The crest or bright area results from constructive interference, whereas the dark
area resulted from destructive interference.
● James Clerk Maxwell (1831-1879) developed a detailed understanding about the nature
of light waves. His theory showed that light is an electromagnetic wave generated by an
oscillation of an electric charge. The oscillation produces electric and magnetic fields
whose motion constitutes a light wave.
● Light, heat, radiowaves, X-rays, etc. make up what we call Electromagnetic Radiation.
● The slice of the electromagnetic spectrum we see is termed Visible light (400-700nm).
● EM waves are described by certain terms:
○ wavelength (λ- lambda): measured from peak to peak in nanometers (nm) = 1 x
○ Each peak to peak is termed a cycle.
○ frequency (υ - nu): Frequency is # of wave cycles per second (sec-1 or Hertz,
● How can we calculate the wavelength, λ- lambda, and/or frequency, (υ - nu)?
● Answer: Speed of Light constant, c
○ c = λ x υ (where c = 3.00 x 108 m/sec)
○ ALL electromagneticwaves travel in a vacuum at the speed of light.
○ WATCHOUT!!! The units in speed of light have the m for meters must be able to
convert from nm’s to m’s. 1 nm = 10-9m
○ Must be able to calculate either λ or υ ;given the other variable.
● Example: What is the wavelength (nm) of a laser light with a frequency of 4.69 x 1014s
○ Use c= y * v
○ y= c/v = 3.0 x 108ms-1 /4.69 x 1014s -1
○ y = 6.4 x 10-7m
○ y (nm) = 6.4 x 10-7m)(1nm/10-9m) = nm
Quantized Energy and Photons:
● History/Discovery – Is light a wave or a particle?
● Johann Balmer (1885): Light as a Wave Different salts placed in the explosives of
fireworks produce colorful displays. Johann Balmer, 1885, studied the different colors
that salts produce in flames.
● White light or sunlight is a distribution of many different wavelengths. When we focus the
white light through a prism, the different colors can be seen.
● Light produced from an excited atom when passed through a prism, produces a series of
discrete lines and blank areas can be recorded on photographic film. This is sometimes
referred to as the visible line spectrum of an atom.
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