Atomic Structure

1
Chapter 7

• Atomic Structure

2
As Chemists we want to understand

• Life, the Universe and Everything
• But..we first need to understand molecules
  bonding.
• To grasp Bonding, we must understand atoms.
• And understanding atoms requires knowledge of the
  electrons.
• We get our info about electrons by studying light.

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But light is a Wave

• So the best place to start, is with the study of
  waves.
• Which will lead us to the observation that an
  electron is a four dimensional vibrating
  wavicle ---sometimes a wave and sometimes a
  particle.

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Parts of a wave
Wavelength
l
Frequency number of cycles in one
second Measured in hertz 1 hertz 1
cycle/second AKA sec-1
5
Frequency n
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Sound vs. Light

• Sound is an example of a compression wave
  requires a medium to propagate.
• Light is a transverse wave that requires no
  medium to propagate

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EMR

• Moving electrons cause magnetism.
• Moving magnets cause electricity.
• Waves of electric and magnetic fields oscillate
  at right angles to each other.
• Light electromagnetic radiation.

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Kinds of EM waves

• There are many different l and n
• Radio waves, microwaves, x rays and gamma rays
  are all examples.
• Light is only the part our eyes can detect.

G
a
m
m
a
R
a
d
i
o
w
a
v
e
s
R
a
y
s
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The speed of light

• in a vacuum is 2.998 x 108 m/s c
• c ln
• What is the wavelength of light with a frequency
  5.89 x 105 Hz?
• What is the frequency of blue light with a
  wavelength of 484 nm?

10
In 1900

• Matter and energy were seen as different from
  each other in fundamental ways.
• Matter was particles.
• Energy could come in waves, with any frequency.
• Max Planck realized that the Photo-electric
  effect couldnt be explained by viewing energy as
  a wave.

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Energy is Quantized

• Planck found DE came in chunks with size hn
• DE n h n
• where n is an integer ( of photons)
• and h is Plancks constant 6.626 x 10-34 J s
• n is frequency
• These packets of hn are called quantum

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Big Idea

• Knowing the color, frequency, wavelength or
  Energy of light you can determine any of the
  others.
• c ln
• E h n
• E hc/l

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Einstein is next

• Said electromagnetic radiation is quantized in
  particles called photons.
• Each photon has energy E hn hc/l
• Combine this with E mc2
• You get the apparent mass of a single photon of
  NRG.
• m h / (lc)

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Soooo..Which is it?

• Are electrons a wave like light, or a particle
  like matter?
• Yes ----(Flat Man)---It is both!
• This concept is called Wave -Particle duality.
  a wavicle

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Matter as a wave

• Using velocity v instead of the frequency (n) we
  get ..
• De Broglies equation l h/mv
• From this we can calculate the wavelength of an
  object.

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Examples

• The laser light of a CD is 7.80 x 102 m. What is
  the frequency of this light?
• What is the energy of a photon of this light?
• What is the apparent mass of a photon of this
  light?
• What is the energy of a mole of these photons?