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Light

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Light Is a Wave Amplitude is the height of the wave from zero to the crest or from zero to the trough

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**Wavelength is the length between waves (how’s that for a definition)**

Measure crest to crest or trough to trough Symbolized with the Greek letter lambda (λ) Greek Lamb

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**Frequency is the number of waves that pass a given point over a period of time**

Commonly measured in the unit Hertz (Hz) or sometimes in s-1 Symbolized with the letter f

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**The speed of light is 3 x 108 m/s**

Symbolized with the letter “c” (latin celeritas = swift) We can draw a relationship between wavelength and frequency with the following equation: c = λf Q: What type of relationship does this represent? A: Inverse

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Try this one! X-rays emitted by Cu have a wavelength of 1.54 x 10-8cm. What is the frequency of this radiation? Answer… 1.95 x 1018 sec–1 (Hz) DO WORK!

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**Calculate the wavelength of yellow light emitted by a sodium lamp**

Calculate the wavelength of yellow light emitted by a sodium lamp. The frequency is 5.0 x 1014 Hz. Answer… 6.0 x 10-7m

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**What is the wavelength of radiation with a frequency of 1.50 x 1013 Hz?**

Answer… 2.00 x 10-5m

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**What frequency is radiation with a wavelength of 5.00 x 10-8m?**

Answer… 6.00x1015 Hz

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**The Electromagnetic Spectrum**

See Page 139 in your book! Made up of radio, micro, infrared, visible light, ultraviolet, X-rays, and gamma rays Visible light makes up only a small portion Can be separated into its constituent colors by using a prism.

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Atomic Spectra Emission Spectra (also referred to as bright line spectra) are the frequencies of light emitted by an element separated into discrete lines Continuous Spectrum is all wavelengths within a given range (usually applied to ROYGBIV) Absorption Spectra are discreet energies absorbed from the continuous spectrum by electrons of a specific element

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Recap… When atoms absorb energy, electrons move into higher energy levels Atoms emit energy when they return to lower energy levels, sometimes in the form of light Atomic emission spectrum – the frequencies of light emitted by an element separated into discrete lines Emission spectrums are the “fingerprint” of an atom

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**Louis de Brolglie predicted that light can behave as a wave as well as a particle.**

Known as the Wave-Particle Duality Theory The Photoelectric Effect occurs when electrons are released from a metal when light is shone on it. This only occurs with certain frequencies of light.

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Max Planck and Albert Einstein ( ) demonstrated that light behaves as if it were composed of tiny “packets” of energy called QUANTA or PHOTONS Energy of a photon (absorbed or emitted) is proportional to the frequency of light

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**We can represent this relationship with an equation!**

E = hf h is known as Planck’s constant. h = 6.63x10-34J s Q: What type of relationship exists between energy and frequency? A: Direct

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Try these… Calculate the frequency of a photon with energy 4.55x10-23 J. E = hf f = E/h f = x10-23 J 6.63x10-34 J s f = 6.86x1010 Hz

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**Calculate the energy of a photon whose frequency is 3.20x1011s-1**

Answer… 2.12x10-22J

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**Inadequacies of Bohr’s Model**

Much like the other models of the atom Bohr’s model had many weaknesses Could only explain the spectra of single atoms with one electron Could not explain why some emission lines are brighter than others

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**As we mentioned before…**

The quantum mechanical model Electron clouds house electrons 90% of the time Based on Schrödinger's equations Werner Heisenberg also contributed to the Quantum mechanical model

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**Heisenberg was the head of the German Nuclear Energy Project under the Nazi regime.**

Heisenberg Uncertainty Principle states that its impossible determine velocity and position of an electron. Epitaph reads, “He lies somewhere here”

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