The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.
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Transcript of The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.
The Electromagnetic Spectrum, Planck, and
BohrHonors Coordinated Science II
Wheatley-Heckman
Electromagnetic Spectrum
• Extends from low to high wavelengths.
Electromagnetic Wave Properties
• λ (lambda) = wavelength – Distance between 2 corresponding points on
adjacent waves.• ν (nu) = frequency
– The number of waves that pass a point during a period of time.
– Units = Hertz (Hz) = 1 wave/second
Constant Speed
• All forms of EM radiation move at a constant speed of c = 3.00 x 108 m/s.
• The relationship between frequency and wavelength can be expressed mathematically:
c = λ ν
Practice Problem #1
•Calculate the frequency of a light wave with a wavelength of 515 nm.
•Hint: You must first convert 515 nm to meters.–515 nm = 515 x 10-9 m
Max Planck• Proposes that objects can only emit
energy in small and specific amounts. • Planck discovers the following
relationship:
• E = energy (measured in Joules)• h = Planck's constant = 6.626 x10-34 J*s• ν = frequency
E = h ν
3 Useful Equations
c h λE =
c = λ ν
E = hν
More Practice Problems
1) Calculate the frequency of a wave with an Energy of 3.75 x 10-6 J.
2) A near infrared wave has a wavelength of 1.00 x 10-6 meters. Calculate the energy of this wave.
Flame TestWhy do different elements emit a different
color of light when exposed to a flame?
Line SpectraWhen the light from the flame is passed through a
prism a spectrum is formed:
• A spectrum that contains only certain colors (wavelengths) is called a line spectrum.
• When different elements are vaporized in the flame, they each produce a unique spectrum: this is a kind of “atomic fingerprint” that can be useful in identifying elements.
• But why does this occur? And where does this energy come from?
The Bohr Model• Niels Bohr combines the ideas of:
– Rutherford (planetary model with a nucleus and circling electrons)
– Planck (quantized amounts of energy)
• Bohr concludes that the energy of the electrons in an atom has to be quantized. This means that electrons can only have certain amounts of energy.
• An electron in the ground state is closest to the nucleus (n=1).
• When it absorbs energy, it enters an excited state and moves to a higher energy level.
Bohr’s Model of the H atom
• Energy is emitted when an electron falls from an excited state to ground state.
• The released energy causes the unique line spectrum.
• Bohr uses his model and Planck’s equation to calculate the frequencies for the line spectrum of hydrogen.
Limitations of the Bohr Model
• Bohr’s model is able to explain the line spectrum for hydrogen, but could not explain the spectra of more complex atoms that have more electrons.