Transcript Electromagnetic Radiation - jsandoe

LEQ:
How are atoms and energy related?
Electromagnetic Radiation
-A form of energy that exhibits wavelike behavior as it
travels through space
Ex: X-ray, UV, Infrared, Microwave, Radiowave, etc..
All of the forms of
electromagnetic radiation
together are the
electromagnetic
spectrum:
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Features of Waves
Wavelength () - distance between corresponding
points of two adjacent waves
*Measured by length (cm, nm, etc…)
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Frequency (v) - number of waves to pass a certain point in a
given amount of time
* Measured in waves/sec
* 1 wave/sec = 1 hertz (Hz)
Longer  = Lower Frequency
* Inverse mathematical relationship
How do we represent the relationship between  and v?
c= v
k= xy - from unit 2!
c = speed of light (m/s)
* 3.00 x 108 m/s
* Same for all electromagnetic radiation!!
Amplitude - distance from the median of the
wave (middle) to the top of a crest
of the wave
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What is the frequency of light that has a
wavelength of 250 m?
c = v
v = c/
v = (3.00 x 108 m/s) / (250 m)
v = 1.2 x 106 s-1 or Hz
What is the wavelength of light that has a
frequency of 2.3 x 1015 Hz?
c = v
 = c/v
 = (3.00 x 108 m/s) / (2.3 x 1015 Hz)
 = 1.3 x 10-7 m or .13 micrometers
Does light always exist in a wave?
Max Planck (1900) suggests that energy is emitted in a small
packet called a quantum, not a continuous wave.
- minimum amount of energy that can be lost or
gained by an atom.
Like the cent. Every time you spend or earn money, it is in a multiple of
number of cents. You can’t spend or earn something less than a cent.
How much energy a quantum is can be calculated:
E = hv
E= energy, measured in joules
h = Planck’s constant = 6.626 x 10-34 J • s
v = frequency
* So electromagnetic radiation is behaving as both a wave
and a set amount of energy???
Albert Einstein (1905) takes Planck’s thoughts further
and suggests electromagnetic radiation has
wave-particle duality
- Light can be thought of as a particle or photon
-A particle of electromagnetic radiation
carrying a quantum of energy
Calculate the energy of a photon that has a
frequency of 1.20 x 1015 Hz
E = hv
E = (6.626 x 10-34 J • s) x (1.20 x 1015 Hz)
E = 7.95 x 10-19 J
Calculate the frequency of a photon with an
energy of 3.90 x 10-19 J.
E = hv
v = E/h
v = (3.90 x 10-19 J) / (6.626 x 10-34 J
v = 5.89 x 1014 Hz
• s)
Bohr Model of the Atom - tweaked!!!!
Why do energy changes in atoms happen in specific
quantities?
Bohr says there are certain orbitals electrons can be in that
surround the nucleus and have certain energy values to them.
Electrons can’t exist between these energy levels.
See page 102 in text book
The lowest energy level the electrons can be in is called the
ground state. When it jumps to another energy level, this is
called an excited state.
Emission - When an electron gives off energy by
dropping to a lower energy level
Absorption - When an electron gains energy to
jump up to a new energy level.
*Electrons can’t exist in between energy levels
**This is why they only absorb or emit energy
in packets called quanta!