Light, Photon Light, Photon Energies, and Atomic Energies, and Atomic

Spectra 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

Wave Properties—Wavelength

Wavelength () is the distance from two consecutives higher or lower points of a wave (measured in meters “m” or “nm”)

wavelength

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)

Lower frequency

Higher frequency

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 ()

Smaller Frequencies ()

Less Energy (E)

Shorter Wavelength ()

Larger Frequencies ()

Higher Energy (E)

Longer Wavelength ()

Smaller Frequencies ()

Less Energy (E)

Shorter Wavelength ()

Larger Frequencies ()

Higher Energy (E)RRooyy GG. B. Biivv

Quick Check: Electromagnetic Spectrum

1. Which type of wave in the electromagnetic spectrum has the greatest energy?

2. Which type of wave has the longest wavelength?

3. List the waves of the visible spectrum in order of increasing energy.

Gamma Rays

Radio Waves

(Lowest Highest)

Red, Orange, Yellow, Green, Blue, Violet

Relationship between Wavelength and Frequency

As the wavelength increases, the frequency of the wave decreases.

Important Note(s)

•Wavelength must be in meters.

•Frequency must be in Hertz.

Example #1A purple light has a frequency of 7.42 x 1014 s-1.  What is its wavelength?

c =f

f

3.00 x 108 m/s= (7.42 x 1014 s-

1)

7.42 x 1014 s-17.42 x 1014 s-1

= 4.04 x 10-7 m

Example #2Certain 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.

c =f

3.00 x 108 m/s= f (3.18 x 10-7 m)3.18 x 10-7 m3.18 x 10-7 m

f = 9.43 x 1014 s-1 or Hz

Example #3: Now You Try!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?

c =f

3.00 x 108 m/s= (5.09 x 1014 Hz)

= 5.89 x 10-7 m

Relationship between Frequency and Energy

As frequency increases, the energy of the wave increases.

Important Note

•Frequency must be in Hertz.

Example #4What is the energy of a photon if it has a frequency of 6.82 x 1017 Hz?

E = hf

f

E =(6.63 x 10-34 J•s) (6.82 x 1017 Hz)

E = 4.52 x 10-16 J

Example #5: Now You Try!Determine the frequency of a wave that has a energy of 8.72 x 10-18 J.

E

E = hf

8.72 x 10-18 J= (6.63 x 10-34 J•s) f

f = 1.32 x 1016 Hz

Putting the Two Together

Example #6What is the energy of a photon of blue light that has a wavelength of 4.5 x 10-7m?

E =(6.63 x 10-34 J•s)(3.00 x 108 m/s)

4.5 x 10-7m= 4.4 x 10-19 J

Atomic Spectrum

How color tells us about atomsAtomic 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