Transcript f - Houston ISD

Light, Photon
Energies, and Atomic
Spectra
 Louis
Electrons and Waves
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 ()
Shorter Wavelength ()
Smaller Frequencies (n)
Larger Frequencies (n)
Less Energy (E)
Roy G. Biv
Higher Energy (E)
Longer Wavelength ()
Shorter Wavelength ()
Smaller Frequencies (n)
Larger Frequencies (n)
Less Energy (E)
Higher Energy (E)
1.
Quick Check: Electromagnetic
Spectrum
Which type of wave in the electromagnetic spectrum
has the greatest energy?
Gamma Rays
2.
Which type of wave has the longest wavelength?
Radio Waves
3.
List the waves of the visible spectrum in order of
increasing energy.(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 #1
f
A purple light has a frequency of 7.42 x 1014 s-1. What
is its wavelength?
c =f 
3.00 x 108 m/s = (7.42 x 1014 s-1) 
7.42 x 1014 s-1
7.42 x 1014 s-1
 = 4.04 x 10-7 m
Example #2
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.
c =f 
3.00 x 108 m/s= f (3.18 x 10-7 m)
3.18 x 10-7 m 3.18 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 #4
What is the energy of a photon if it has a frequency f
of 6.82 x 1017 Hz?
E = hf
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 E
of 8.72 x 10-18 J.
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 #6
What is the energy of a photon of blue light that has a
wavelength of 4.5 x 10-7m?
-34 J•s) (3.00 x 108 m/s)
(6.63
x
10
E=
= 4.4 x 10-19 J
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