1. The ELECTRON:
Wave Particle Duality
“No familiar conceptions can be woven
around the electron. Something unknown is
doing we don’t know what.”
-Sir Arthur Eddington
The Nature of the Physical World (1934)

2. The Electron
• Discovered by JJ Thomson in 1897.
• Used Cathode Ray tubes.
• Electron beam appeared regardless of material used 
Must be a part of all atoms.
• Repeled by a negatively charged plate, attracted to
positive  Must have negative charge.
• Did not appreciably affect atoms overall mass must
be virtually weightless.

3. The Problems With the
Rutherford Model
• Where are the electrons really at?
• Electrons outside the nucleus are
attracted to the protons in the nucleus
– What keeps the atom from
collapsing?
• How can different elements that have
similar composition, have such
different properties?

4. The Missing Key
• The key piece of indirect evidence that led to the
advancement of atomic theory came from Robert
Bunsens flame tests.

5. The Observation that different
elements gave off uniquely
colored flames led chemists to
take a closer look at light.

6. Light as Waves
• Waves carry energy.
• Conventional wisdom holds that light is a transfer
of energy through the wavelike vibration of the
universes electric and magnetic fields.
– Electromagnetic Radiation

7. Electromagnetic radiation propagates through
space as a wave moving at the speed of light.
c = 
c = speed of light, a constant (3.00 x 108 m/s)
 = frequency, in units of hertz (hz, sec-1)
 = wavelength, in meters

8. The energy (E ) of electromagnetic radiation
is directly proportional to the frequency ()
of the radiation.
E = h
E= Energy, in units of Joules (kg·m2/s2)
h= Planck’s constant (6.626 x 10-34 J·s)
= frequency, in units of hertz (hz, sec-1)

9. Long
Wavelength Wavelength Table
=
Low Frequency
=
Low ENERGY
Short
Wavelength
=
High
Frequency
= *Wavelength and Frequency are
High ENERGY Indirectly Proportional

10. Answering the Dilemma of the
“Collapsing” Atom
• Treat electrons as waves
• As the electron moves toward the
nucleus, the wavelength shortens
• Shorter wavelength = higher energy
• Higher energy = greater distance
from the nucleus

11. The Wave-like Electron
The electron propagates
through space as an energy
wave. To understand the
atom, one must understand
the behavior of
electromagnetic waves.
Louis deBroglie

12. COLOR
•Waves of light can have a wide range of frequencies
and wavelengths.
•The energy of a beam of light of light corresponds
to defined colors.
•Visible Light falls somewhere between Red (Low
Energy) andViolet (High Energy)
•This range of frequencies and wavelengths is
known as the electromagnetic spectrum

13. The Electromagnetic Spectrum

14. Separating Light

15. White Light
•The electromagnetic
spectrum is continuous- there
is no part of it that does not
correspond to a unique
wavelength or frequency of
light.
•White Light (such as sunlight)
contains light at all
wavelengths of the spectrum.
•The different frequencies of
light can be separated when
passed through a prism.
•Known as an emission
spectrum.

16. Under the Wave Model of the
Electron one would expect to see
a continuous emission spectra (all
colors) because the electron’s
wavelength gradually changes as
it moves towards or away from
the nucleus.

17. Spectroscopic analysis of the hydrogen
spectrum…
…produces a “bright line” spectrum

18. PROBLEM!
• When you filter the light emitted
from heated materials through a
prism you DO NOTproduce a
continuous spectrum.
• Heated objects only produce light
at specific frequencies.

19. Emission Spectra
The specific frequencies of light emitted are unique to specific elements.
-Therefore emission spetcra can be used as an identification tool.

20. Quantum Theory
• The observation that light was not emitted in a
continuous spectra (but rather at specific
frequencies) led German Physicist Max Planck to the
surprising conclusion that matter can only gain or
loose energy in small specific amounts.
• Quantum:Specific amount of energy that can be
gained or lost by an atom. (You can only have whole
quantum numbers)
• Photon:Packet of electromagnetic radiation that
carries one quantum of energy.
• When you add energy and excite atoms (such as in a
neon sign) photons are absorbed- they can then be
released emitting light of a particular corresponding
frequency.

21. Bohr Model (1913)
• Electrons orbit the nucleus in
circular paths of fixed
energy.
– Called energy levels,
electron shells, or quantum
shells (all terms for the
same thing).
• Electrons can jump from
energy level to energy level.
• Electrons absorb or emit light
energy when they jump from
one energy level to another.

23. Energy Levels
• The energy levels are like the
rungs of a ladder but are not
equally spaced.
– It requires different amounts
of energy to be absorbed or
emitted for the electron to
jump betweendifferent levels.
• Energy emitted by the electron as
it leaps from the higher to the
lower energy level is proportional
to the frequency of the light
wave.
– Frequency define the color of
visible light.

24. Reexamining the Quantum
• A quantum of energy
is the amount of
energy required to
move an electron
from one energy
level to another.
• Photons are bundles
of light energy that
is emitted by
electrons as they go
from higher energy
levels to lower
levels.

25. Energy of a Photon
Energy of the emitted photon = Difference in energy between two states
E=h
E=energy
=frequency
h=Plank’s constant 6.7x10-34Js

26. Emission Spectrum
• Since the energy of a
photon released
corresponds to the
energy difference
particular jump made,
you get photons of
different energies (and
hence frequency).
– Frequency defines
the color of light.
– Explains unique
emission spectrum

27. Hydrogen
• Bohr developed his model
by working with hydrogen.
• His model explained the
emission spectrum of the
hydrogen atom but did not
always explain those of
other elements.

28. So Neither Model is Perfect...
• How can you have you cake and eat it too?
– Answer: Combine the models.
• The electron can situationally act as either a wave
or a particle.
– We call this “Electron Duality”

29. Wave-Particle Duality
JJ Thomson won the Nobel prize for firstdescribing
the electron as a particle.
His son, George Thomson won the Nobel prize for
describing the wave-like nature of the electron.
The
electron is
a particle!
The
electron is
an energy
wave!