1. Unit 3: Light and Electrons

2. Electromagnetic Radiation
Light is electromagnetic radiation: combined electric and magnetic waves
Source
Electric vector
Magnetic vector
direction of propagation

3. Electromagnetic Radiation
Light is more than what we can see…

4. Electromagnetic Radiation
Subatomic particles (electron, photon, proton, etc) exhibit both PARTICLE and WAVE properties. This is known as Wave-Particle Duality.
Diffraction: wave-like
Photoelectric Effect: particle-like

5. Electromagnetic Radiation
Wave Properties of Light:
It’s fast! …c = 3.0 x 108 m/s
It relfects, refracts, diffracts (Transverse wave)

6. Electromagnetic Radiation
All light waves have frequency wavelength
symbol: ν (Greek “nu”) l (Greek “lambda”)
units: “cycles per sec” = Hertz “distance” (m, nm)
c = l · ν
where c = speed of light
= 3.00 x 108 m/sec
Increasing frequency

7. Electromagnetic Radiation
Example: Red light has l = 700. nm.
Calculate the frequency, f. =
3.00 x 10 8
m/s
700. x 10 -9 m
4.29 x 10 14 /s
ν = C l

8. Electromagnetic Radiation
Particle Properties of Light:
A particle of light is called a photon
Energy of a photon is calculated by E = h · ν
where E = energy (Joules, J)
ν = frequency (Hertz, Hz, 1/sec)
h = Planck’s constant 6.63 x J·s
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9. Electromagnetic Radiation
Albert Einstein postulates the Photoelectric Effect to explain two observations:
No electrons are observed until a minimum energy is applied.
Number of electrons ejected depends upon light intensity – not light frequency!

10. Light is created by the Photoelectric Effect

11. Electromagnetic Radiation
The photoelectric effect and the idea of discrete, quantized energies neatly explain the observation of emission spectra.

12. Electromagnetic Radiation
Example: Red light has l = 700. nm.
Calculate the energy per photon.
E = hν and c = lν
So ν = c/l and E = hc/l
E = (6.63 x Js)(3.0 x 10 m/s) x m
E = 2.84 x J
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13. Electron Orbitals Electron Orbitals
While thinking about the emission spectrum of hydrogen, Neils Bohr came up with the planetary model of the atom. In this model, electrons can only orbit the nucleus at discrete distances and particular orbital shape.
Orbital model of Na
Sharp-line spectrum of H
Neils Bohr