10/26/09
Quantum Model of the Atom
Location and Behavior of Electrons
Electrons as Waves
  Bohr’s
work did not explain atoms
other than hydrogen.
  Electron thought to be like light, both a
wave and a particle.
  Electrons, like light, can be diffracted
(bent).
  Electrons can also behave as particles.
  So how about this?
Quantum Numbers
  Denote
the properties of atomic orbitals
and characterize the electrons within
them.
  There are four quantum numbers that
characterize any given electron.
  The first three come from the
Schrödinger equation.
  The fourth describes the state of the e-.
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Electron Locations
  This
is a model providing a method for
prediction.
  We use a four number address system
to place electrons.
  This is an arbitrary system designed to
place electrons…the electrons don’t
know they have a home.
Principle Quantum Number
  n,
indicates main energy levels
occupied by electrons.
  Whole numbers starting at 1 up to 7.
  The larger the number the more energy
and the further away from the nucleus
the e- is.
  More than one e- can have the same n.
  The total # of orbitals in an energy level
= n2 (energy level = shell).
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Running Example
  Hydrogen:
  n
1 electron
=1
Take a look at the PT
  How
many rows are there??
just learned that there are how
many energy levels??
  Oh how wonderfully things fit together
  You
Angular Momentum Quantum
Number
  l,
indicates the shape of a subshell.
number is related to the shapes of
orbitals.
  l = n – 1
  0 = s
1=p
2=d
3=f
  Values for l are the numbers…letters
correspond to the shapes.
  This
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Cont’d
  Ex.
n = 1, one subshell: s

n = 2, two subshells: s and p

n = 3, three subshells: s, p, and d.
Ex. n = 2 has 2s and 2p
Shapes, S
Shapes, p
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Shapes, d
Shapes, f
Running Example
  Hydrogen:
1 electron
=1
  l = 0 (n-1 = l), so the shape of the
orbital is a sphere
  n
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Magnetic Quantum Number
  Describes
the orientation of the
subshells (m).
  m = values between -l and l
  s=1
p=3
d=5
f=7
  Each subshell can have the above
number of orientations (called orbitals).
  Each orientation can contain 2
electrons.
Examples
  If
l =2 then…
the range of m = -2, -1, 0, +1, +2
  Each value for m corresponds to one of
the 5 orientations (orbitals) for the d
subshell.

Running Example
  Hydrogen:
1 electron
=1
  l = 0 (n-1 = l), so the shape of the
orbital is a sphere.
  ml = 0
  n
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Spin Quantum Number
  Distinguishes
between the two
electrons found in m.
  Can either be +1/2 or -1/2
  The four numbers together provide an
address for the location of an electron
in an atom.
Running Example
  Hydrogen:
1 electron
=1
  l = 0 (n-1 = l), so the shape of the
orbital is a sphere.
  ml = 0
  Spin = + 1/2
  n
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Example: He-4 has 2 e-
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