Electromagnetic Spectrum

1
Electromagnetic Spectrum

• Using physics to further progress the model of
  the atom

2
Rutherfords problems withhis model of the atom

• Rutherford used his gold foil experiment to
  propose a new model of the atom.
• In this experiment he concluded that the atom
  needed to have a dense positive nucleus at its
  center

3
Rutherfords problems withhis model of the atom

• His model is referred to as the SOLAR SYSTEM
  MODEL where the nucleus represents the sun and
  the electrons orbit around the nucleus.
• Though this was a big step forward in the
  development of the atom it didnt explain some
  very common characteristics of matter.

4
Observations
5
Visible Light

• We are all familiar with light but what is
  visible is just a very, very small portion of
  the electromagnetic spectrum
• What colors make up the rainbow?
• Red, Orange, Yellow, Green, Blue, Indigo, Violet
  (ROYGBIV)

6
The E-M Spectrum
X-rays(Cancerous in large doses small doses
medical scanning)
Ultraviolet ( not as harmful - sunburn black
lights)
Radio Rays(TV, Radio, other communications)
Microwaves(Cooking, communications)
Gamma Rays(Very Harmful / Cancerous)
Infrared(Heat, communication)
7
Parts of a wave
Amplitude
8
Formula for determining wave characteristics

• c ??
• c speed of light 3.00 x 108 meters/sec
• ? wavelength meters
• ? frequency sec-1 or Hertz

9
Formula for determining wave characteristics

• E h?
• E Energy of the wave (Joules)
• h Planks constant 6.626 x 10-34 J sec
• ? frequency sec-1 or Hertz

10
Practice Problems

• Using c ?? calculate the missing variable
• c 3.00 x 108 m/s
• 1. X-rays have wavelengths in the region of 10-1
  nm. What is frequency of these waves?
• 2. One my favorite radio stations broadcasts at
  90.9 MHz. What is the length of the waves being
  emitted from the radio tower?

11
Science Prefixes

• Pico (pm) 10-12
• Nano (nm) 10-9
• Micro (µm) 10-6
• Milli (mm) 10-3
• Centi (cm) 10-2
• Kilo (km) 103
• Mega (Mm) 106
• Giga (Gm) 109

12
So why is the electromagnetic spectrum so
important to chemistry?

• Remember the black body radiation of the
  overheated steel
• Why is the steel emitting light when it is
  heated?
• We take it for granted that when things get hot
  they turn red then orange and finally white but
  that isnt good enough any more

13
Black Body Radiation Colors
C Subjective color
480 faint red glow
580 dark red
730 bright red, slightly orange
930 bright orange
1100 pale yellowish orange
1300 yellowish white
gt 1400 white (yellowish if seen from a distance through atmosphere)
14
Colors and Chemistry

• Steel is a complex metal alloy which is much too
  complicated to try to work out this oddity in the
  behavior of matter.
• So if you had to pick something simple to start
  our understanding of this phenomena what would
  you pick?

15
Colors and Chemistry

• Hydrogen

410 nm
434 nm
486 nm
656 nm
16
Niels Bohr and the Bohr model of the atom

• Bohr hypothesized that instead of haphazardly
  orbiting the nucleus, electrons had clearly
  defined orbits very similar to the planetary
  orbits circling our sun
• His model is (cleverly) named the Planetary Model

17
The Planetary Model of the Atom

• Science cant just make a claim without some
  proof to back it up (that is the job of Religion)

Pay no attention to the comment just presented
and then feebly scribbled out. Religion gives
hope and comfort to millions of human beings and
it is our policy not to question the faith of any
of our students! This teacher (or
ex-soon-to-be-teacher) will learn his lesson soon
enough. - Management
18
Bohrs Proof

• Bohr said this If you assume that the electrons
  have clearly defined orbits that are congruent to
  the energy levels

19
Bohrs Proof

• then when an electron gets excited it jumps
  to a higher energy level. When it relaxes it
  emits a certain wavelength of light.

20
Bohrs Proof
1
1
1
-
1.097373 x 107 m-1
nr2
ne2
?
n7
n6
n5
n4
Paschen Series (ir)
n3
Balmer Series (vis and uv)
n2
Lyman Series (uv)
n1
21
Colors and Chemistry

• Hydrogen

410 nm
434 nm
486 nm
656 nm
22
Hydrogen to Steel

• If Hydrogen emits 4 distinct wavelengths of light
  when its one electron is excited what can we
  extrapolate to that of steel which is made mostly
  of iron?
• http//jersey.uoregon.edu/vlab/elements/Elements.h
  tml

23
Good News Bad News

• Good News
• Bohrs Model works and moves us along in the
  development of the Atomic Theory
• End of this little unit

• Bad (Frustrating) News
• Lots of Math
• Everything I taught you only works for Hydrogen
  and therefore is completely wrong and obsolete.

24
References

• Gold Foil Experiment http//www.youtube.com/watc
  h?v5pZj0u_XMbc
• Glow in the dark cats http//cosmiclog.msnbc.msn
  .com/archive/2007/12/13/514602.aspx?GT110645
• Bright Line spectrum Applet
• http//jersey.uoregon.edu/vlab/elements/Elements.h
  tml

25
Warm Up Quiz

• c ?? Eh?
• c3.0 x108 m/s h6.626 x 10-34 J s
• What is the frequency of a radar photon with an
  energy of 7.2 x 10-24 J?
• What is the frequency of light having a
  wavelength of 6.20x10-7m?