The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

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The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman

Transcript of The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

Page 1: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

The Electromagnetic Spectrum, Planck, and

BohrHonors Coordinated Science II

Wheatley-Heckman

Page 2: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

Electromagnetic Spectrum

• Extends from low to high wavelengths.

Page 3: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

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

Page 4: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

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

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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

Page 6: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

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

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3 Useful Equations

c h λE =

c = λ ν

E = hν

Page 8: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

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.

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Flame TestWhy do different elements emit a different

color of light when exposed to a flame?

Page 10: The Electromagnetic Spectrum, Planck, and Bohr Honors Coordinated Science II Wheatley-Heckman.

Line SpectraWhen the light from the flame is passed through a

prism a spectrum is formed:

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• 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?

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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.

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• 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.

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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.

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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.