1. CHAPTER 4 Electron Configurations (current model of the atom)
deBroglie, Davisson, Germer (wave nature of the electron)
Heisenberg’s Uncertainty Principle
Bohr in 1922
Bohr…
observation of discrete emission spectra…
 quantized energy levels for electrons
 “planetary” model for the atom
(used classical mechanics and electrostatics)
model worked for H atoms … only… 1e-, 1p
amount of radiant energy released/absorbed
as electrons move between orbits matched Bohr’s predictions
BUT … did not correctly predict the spectrum
of any other substance
so…. model must be incomplete

2. Bohr’s work was doomed…
used classical mechanics (physics)
Classical mechanics is the study of the motion of bodies (including the special case in which bodies remain at rest) in accordance with the general principles first enunciated by Sir Isaac Newton in his Philosophiae Naturalis Principia Mathematica (1687), commonly known as the Principia.

3. Bohr’s work was doomed…
used classical mechanics (physics)
… to describe a body (the electron)
that does NOT OBEY Newton’s Laws…
it obeys the laws of quantum mechanics
why? you ask…
well, the electron is not a particle … huh?
what is it??!!??

4. how can something be both!?
LEAP!
The next step towards the structure of the atom (where the electrons can be)
was to realize that the electron (which up to this point we have described as a particle)
can behave like a wave.
remember…. wave – continuous
particle – discrete
how can something be both!?
we have looked at the wave and particle nature of light
(wave-particle duality)
wave properties
particle properties
diffraction
interference
reflection
photoelectric effect
discrete emission spectra
(absorption/emission of single
photons as electrons move
between orbits)

5. tells me whether light is a wave or a particle I’ll write my check.”
“Once and for all I want to know what I’m paying for. When the electric company
tells me whether light is a wave or a particle I’ll write my check.”

6. Wave-particle Duality of Matter
deBrogle 1925
hypothesis : matter has both wave and particle properties (wave-particle duality)
predicted that a particle of mass m and velocity v
should have a wavelength  associated with it
has properties of waves (continuous)
has properties of particles (discrete)
Planck’s constant
(again!)
Davisson and Germer
observed diffraction and constructive interference (wave properties)
of electrons by a crystal of nickel

7. Diffraction and Interference of Light paths of constructive
detector
dark
the slits have
to be
small
AND
the separation
between them (d)
has to be~ 
~ 100’s nm
( m)
beam of light
(beam of photons)
diffraction grating

8. e- e- Diffraction and Interference of Electrons detector “dark”
crystal of metal
(ex: Ni / Al)
each “dot” represents
an atom
have to have
a beam of e-
to observe
the diffraction/
interference
pattern
beam of electrons e-
the separation between atoms in the
crystal must be ~ e-
- separation b/w atoms ~10-10 m
- e- ~ m

9. The diffraction pattern on the left was made by a beam of x-rays passing through
thin aluminum foil. The diffraction pattern on the right was made by a beam of
electrons passing though the same foil.

10. size of an electron – re- = 2.82  10-15 m
Wave Nature of Matter
Louis de Broglie
for an electron
e- = =
speed of the e-
in the n=1 orbit
of H atom
6.626  J s
( 9.11  kg )
( 2.19  106 m/s )
3.32  m (or 3.32 )
size of an electron – re- = 2.82  m
e- > re-
so…. Slide 11 … there’s plenty of room for
the electrons to get through the “grid”

11. Wave Nature of Matter
Louis de Broglie
for a body of mass 50 kg walking - “me”
me = =
6.626  J s
( 50 kg )
( 1 m/s )
1  m
size of “me” – rme = 0.5 m
me < rme
to observe the diffraction (wave property) of “me”
- there has to be a beam of “me’s”
- and, the “me’s” have to go through slits separated
by d ~ me …… IMPOSSIBLE

12. Wave Nature of Matter
Louis de Broglie
for a body of mass 50 kg walking – “me” me =
1  m
to observe the diffraction (wave property) of “me”
- there has to be a beam of “me’s”
- and, the “me’s” have to go through slits separated
by d ~ me …… IMPOSSIBLE
how fast (or slow) would “me” have to be moving for me = 1 m ?
6.626  J s
me (1 m) =
v =
( 50 kg )
( v )
can’t experience
wave properties
because need to be
moving to do so
1  m/s
imperceptibly slow

13. Is the electron a wave? or is it a particle?

14. e- e- go back Diffraction and Interference of Electrons detector
“dark”
crystal of metal
(ex: Ni / Al)
each “dot” represents
an atom
have to have
a beam of e-
to observe
the diffraction/
interference
pattern
beam of electrons e-
the separation between atoms in the
crystal must be ~ e-
- separation b/w atoms ~10-10 m
- e- ~ m
go back

15. Heisenberg Uncertainty Principle
Werner Heisenberg 1933
Heisenberg Uncertainty Principle
terrifically! complex … for us, the key idea is
you cannot ______________ know _________
the __________ and ___________ of a particle
quantitatively…
the uncertainty of position (x) ________
the uncertainty of momentum (mv) __________
simultaneously
exactly
position
momentum
(x)
(mv)
(x)
(mv)
insignificant for BIG objects (like us)
for tiny objects,
like the electron
(me kg, re m)
becomes significant

16. by the numbers….

17. The Uncertainty Principle
qualitatively… for an electron
how do you
determine the position of a particle (________ the electron)
and how fast it is going (two points in time)
when…
you can’t see the particle!

18. ouch... You ____ the electron untethered can’t move …. free!
to find the electron
precisely
need to “poke” around it
with something smaller than ____ the electrons
say, perhaps, a photon

19. You
____ the electron
untethered
…. free!
can’t move
to find the electron
precisely
to find the edges,
need to throw a “lot” of photons… fast, and all at once
____ the electron gets pushed…
no longer where it was…
so, in the act of finding ___ the electron…. it is lost

20. can’t ever know precisely where an electron is
You
____ the electron
untethered
…. free!
can’t move
to find the electron
precisely
can’t ever know precisely where an electron is
(or in fact, where anything is…)