Light, Photon Energies, and Atomic Spectra

Light, Photon Energies, and Atomic Spectra

Electrons and Waves • Louis deBroglie proposed the dual nature of matter, which means that matter has matter-like properties and wave-like properties. • What are wave-like properties? • Wavelength • Frequency • Energy

wavelength Wave Properties—Wavelength • Wavelength () is the distance from two consecutives higher or lower points of a wave (measured in meters “m” or “nm”)

Lower frequency Higher frequency Wave Properties—Frequency • Frequency () is the number of times a wave completes a cycle in one second (cycles per second is “Hertz” or “Hz” or 1/ s or s-1)

Light is Electromagnetic Radiation • Electromagnetic energy is energy that has electric and magnetic fields • There are many types of Electromagnetic Radiation…visible is just one type!

Electromagnetic Spectrum Longer Wavelength (l) Smaller Frequencies (n) Less Energy (E) Shorter Wavelength (l) Larger Frequencies (n) Higher Energy (E) RoyG. Biv Longer Wavelength (l) Smaller Frequencies (n) Less Energy (E) Shorter Wavelength (l) Larger Frequencies (n) Higher Energy (E)

Quick Check: Electromagnetic Spectrum Gamma Rays Radio Waves (Lowest  Highest) Red, Orange, Yellow, Green, Blue, Violet Which type of wave in the electromagnetic spectrum has the greatest energy? Which type of wave has the longest wavelength? List the waves of the visible spectrum in order of increasing energy.

Relationship between Wavelength and Frequency • Important Note(s) • Wavelength must be in meters. • Frequency must be in Hertz. As the wavelength increases, the frequency of the wave decreases.

Example #1 f c =f l = (7.42 x 1014 s-1) l 3.00 x 108 m/s 7.42 x 1014 s-1 7.42 x 1014 s-1 l = 4.04 x 10-7 m A purple light has a frequency of 7.42 x 1014 s-1. What is its wavelength?

Example #2 c =f l (3.18 x 10-7 m) = f 3.00 x 108 m/s 3.18 x 10-7 m 3.18 x 10-7 m f = 9.43 x 1014 s-1 or Hz Certain elements emit light of a specific wavelength when they are burned. For example, silver emits light with a wavelength of 3.18 x 10-7 m. Determine the frequency of the wave emitted by silver.

Example #3: Now You Try! c =f l 3.00 x 108 m/s=(5.09 x 1014 Hz) l l = 5.89 x 10-7 m The yellow light given off by a sodium vapor lamp used for public lighting has a frequency of 5.09 x 1014 Hz. What is the wavelength of this radiation?

Relationship between Frequency and Energy • Important Note • Frequency must be in Hertz. As frequency increases, the energy of the wave increases.

Example #4 f E = hf (6.63 x 10-34 J•s) (6.82 x 1017 Hz) E = E = 4.52 x 10-16 J What is the energy of a photon if it has a frequency of 6.82 x 1017 Hz?

Example #5: Now You Try! E E = hf = (6.63 x 10-34 J•s) f 8.72 x 10-18 J f = 1.32 x 1016 Hz Determine the frequency of a wave that has a energy of 8.72 x 10-18 J.

Putting the Two Together (6.63 x 10-34 J•s) (3.00 x 108 m/s) E = = 4.4 x 10-19 J 4.5 x 10-7m Example #6 What is the energy of a photon of blue light that has a wavelength of 4.5 x 10-7m?

Atomic Spectrum How color tells us about atoms Atomic Emissions

Energy in Atoms A Closer Look at the Spectra and Bohr’s Model of the Atom

What does this have to do with electron arrangement in atoms? • When all electrons are in the lowest possible energy levels, an atom is said to be in its GROUND STATE. • When an atom absorbs energy so that its electrons are “boosted” to higher energy levels, the atom is said to be in an EXCITED STATE.

Atomic Spectrum • Each element gives off its own characteristic colors. • Can be used to identify the atom. • That is how we know what stars are made of. • Bright Line Emission Spectra • Energy Levels and Spectra movie

These are called line spectra • unique to each element. • These are emission spectra

Light, Photon Energies, and Atomic Spectra