1. Waves and the EM Spectra
College Chemistry

2. Waves
Light travels similar to boat waves or a sine/cosine graph (up and down motion)
Has amplitude, wavelength, frequency, and speed
Waves transfer energy, NOT matter

3. Waves Amplitude – height of wave
Brightness of wave (light) depends on amplitude
Wavelength – distance between two crests or two troughs, one complete cycle
Frequency – how fast the wave oscillates up and down
Speed – light moves at a CONSTANT speed
Speed of light: 3.00 x 108 m/s

4. Waves
Speed, frequency, and wavelength are all interrelated and dependent on one another
l = c/v
l = wavelength
c = speed of light (3.00 x 108 m/s)
v = frequency (Hertz or Hz)

5. Example 7.1
Calculate the speed of a wave whose wavelength and frequency are 17.4 cm and 87.4 Hz, respectively.
l = c/v
17.4 = c/87.4 Hz
c = 1.52 x 103 cm/s

6. Light Light waves are a type of electromagnetic radiation, or EM
Electromagnetic radiation – consists of electric and magnetic fields oscillating perpendicular to one another

7. Electromagnetic, EM, Spectrum
All light waves fall onto the EM spectra!!
This includes visible light that we see, and non-visible light that we do not see
Visible light takes up less than 1” on the whiteboard of all light!!

8. EM Spectrum

9. Example 7.2
The wavelength of the green light from a traffic signal is centered at 522 nm. What is the frequency of this radiation?
l = c/v
522 nm x (1 x 10-9 m / 1 nm) = 5.22 x 10-7 m
5.22 x 10-7 m = 3.00 x 108/v
v = 5.75 x 1014 Hz
WAVELENGTHS MUST ALWAYS BE IN METERS FOR THIS EQUATION! ANSWERS WILL BE IN METERS TOO!

10. Beginnings of Quantum Theory m- Max Planck
Planck noticed the radiation (or energy) emitted by an object changes at different temperatures
He suggested that there was a restricted on the amount of energy an object emits or absorbs – called these pieces of energy a quantum
Quantum – fixed amount

11. Max Planck
Think of a quantum as a staircase – you can be on one stair or another stair, but not in between
This quantum of energy = 6.63 x J/s
All objects have to absorb/emit energy that are multiples of this number!!!
We don’t notice it, because this is an extremely small number

12. Photoelectric Effect
In the photoelectric effect, electrons are ejected from the surface of a metal when lights shines on it
A minimum amount of energy is needed to release electrons
This is how different colors from fireworks are made!
Einstein proposed light consisted of quantas of energy - photon

13. Photoelectric Effect
Photon – particles of light that each must possess energy
E = hv
E = energy v = frequency
h = Planck’s constant (6.63 x s)
Planck’s theory did explain the photoelectric effect satisfactorily  but it did not explain the wavelike behavior of electrons…

14. Dual Nature of Energy
Energy is a particle and behaves like a particle (collides with other particles)
Energy is also a wave and behaves like a wave (travels at speed of light and has a frequency/wavelength)
Check Out:

15. Example 7.3
Calculate the energy (in J) of a photon w/ a wavelength of 5.00 x 104 nm (IR) and
We know E = hv AND v = c/l
x 104 nm (1.0 x 10-9 m / 1 nm) = 5.00 x 10-5 m
2. v = 3.00 x 108 m/s / 5.00 x 10-5 m = 6 x 1012 Hz
3. E = (6.36 x J*s)(6 x 1012 Hz) = 3.8 x J

16. Meters to nanometers
1 m = 109 nm
1 nm = 10-9 m
Memorize!