Electron As a Particle and Wave Electrons get excited when energy is absorbed by using heat or electrical energy Electrons get excited when energy is absorbed by using heat or electrical energy Excited electrons move back to their ground state when they release the same amount of energy that was absorbed (conservation). Excited electrons move back to their ground state when they release the same amount of energy that was absorbed (conservation). Light energy (electromagnetic radiation) is released when an electron returns to a lower energy level Light energy (electromagnetic radiation) is released when an electron returns to a lower energy level

Light Energy Light travels as a wave and is made of photons. Light travels as a wave and is made of photons. Light contains quanta energy called photons (Einstein) Light contains quanta energy called photons (Einstein) Speed of light in a vacuum 3.0 x 10 8 m/s Speed of light in a vacuum 3.0 x 10 8 m/s How fast is that?? How fast is that?? It would take 2.5 seconds for radar waves traveling at the speed of light to travel 478,000 miles -- leave the earth, bounce off the moon and return!! It would take 2.5 seconds for radar waves traveling at the speed of light to travel 478,000 miles -- leave the earth, bounce off the moon and return!!

Speed of Light c = the speed of light c = the speed of light c = λv c = λv λ = wavelength λ = wavelength v = frequency v = frequency Wavelength: one wave, the distance of one crest and one trough (Unit: meters) Wavelength: one wave, the distance of one crest and one trough (Unit: meters) Frequency: # of waves per second (Unit: s -1 or Hertz, Hz) Frequency: # of waves per second (Unit: s -1 or Hertz, Hz)

The Electromagnetic Spectrum Radio Waves Radio Waves Microwaves Microwaves Infrared Radiation Infrared Radiation VISIBLE LIGHT VISIBLE LIGHT ROY G BV ROY G BV Ultraviolet Ultraviolet X-Rays X-Rays Gamma Rays Gamma Rays Low Frequency, Long Wavelengths Low Frequency, Long Wavelengths v = Hz λ = m v = Hz λ = m VISIBLE LIGHT VISIBLE LIGHT 400 – 800 nanometers 400 – 800 nanometers Nanometer = m Nanometer = m High Frequency, Short Wavelengths High Frequency, Short Wavelengths v = Hz λ = m v = Hz λ = m

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Max Planck Energy is absorbed and emitted in discrete units of light energy called quanta (also known as photons) Energy is absorbed and emitted in discrete units of light energy called quanta (also known as photons) The energy of a light quantum corresponds to the energy difference between two energy levels. The energy of a light quantum corresponds to the energy difference between two energy levels. E = h υ E = h υ Energy is equal to Planck’s constant multiplied by frequency Energy is equal to Planck’s constant multiplied by frequency h = 6.63 x J s h = 6.63 x J s

Photoelectric Effect Absorption of light striking a metal with a certain frequency, has enough energy to release an electron (photon) of light Absorption of light striking a metal with a certain frequency, has enough energy to release an electron (photon) of light

Sample Problems Yellow light with a frequency of approximately 6.0 x Hz is the predominant frequency in sunlight. What is the energy of this light? Yellow light with a frequency of approximately 6.0 x Hz is the predominant frequency in sunlight. What is the energy of this light? 4.0 x J 4.0 x J A quantum of a certain color of visible light is found to have an energy of 5.0 x J. What is the color of this light? A quantum of a certain color of visible light is found to have an energy of 5.0 x J. What is the color of this light? Violet because the frequency is 7.5 x Hz which is equivalent to 400 nm (the shortest wavelength for light) Violet because the frequency is 7.5 x Hz which is equivalent to 400 nm (the shortest wavelength for light)

Changing Energy Levels Excited State: Excited State: When an e - has gained energy to jump to a higher energy level When an e - has gained energy to jump to a higher energy level Ground State: Ground State: Most stable (original location of the electron) Most stable (original location of the electron) Excited electrons lose energy to return to stability Excited electrons lose energy to return to stability This releases energy as electromagnetic radiation (a photon of light) This releases energy as electromagnetic radiation (a photon of light)

Conservation of Energy The energy absorbed always equals energy emitted. The energy absorbed always equals energy emitted. Recall that electrons can not be in between energy levels; however electrons can skip and move up 2,3,4… levels at a time. Recall that electrons can not be in between energy levels; however electrons can skip and move up 2,3,4… levels at a time. The energy is released similarly. Either in large amounts (drop back several energy levels) or the electrons can jump back one energy level at a time. The energy is released similarly. Either in large amounts (drop back several energy levels) or the electrons can jump back one energy level at a time.

Photoelectric Effect Electron as a particle is ejected from the surface of a metal exposed to a specific frequency of light Electron as a particle is ejected from the surface of a metal exposed to a specific frequency of light Photon “a packet of light” Photon “a packet of light” E = h E = h otoelectric+effect+video&FORM=VIRE1#vi ew=detail&mid=63FE23E8E374EEB1237C6 3FE23E8E374EEB1237C