EMR info

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EMR info
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Waves, light, and energy Where chemistry and
physics collide
http//imagers.gsfc.nasa.gov/ems/waves3.html
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First things first Waves
a and b represent wavelength (?)- the distance of
a wave from crest to successive crest measured
in meters
http//www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSp
ec.html
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Waves amplitude
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• The height of a wave from crest to midline or
  trough to midline measured in meters

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Terms you need to know
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• Wavelength (?)
• Amplitude
• Frequency (v I know some of you have used f,
  move on and get with chemistry!)
• the number of cycles per second
• measured in cycles per second (s-1) or Hz (Hertz)
• Propagation of electromagnetic waves

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http//www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSp
ec2.html
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http//micro.magnet.fsu.edu/primer/lightandcolor/i
mages/electromagneticfigure1.jpg
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http//lepus.physics.ualr.edu/tahall/EXAM2/emspec
.jpg
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http//www.arpansa.gov.au/images/emsline2.gif
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Visible Light
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• color wavelength(Å) f(1014 Hz) Energy
  (10-19 J)
• Violet 4000---4600 7.5--6.5 5.0--4.3
• Indigo 4600---4750 6.5--6.3 4.3--4.2
• Blue 4750---4900 6.3--6.1 4.2--4.1
• Green 4900---5650 6.1--5.3 4.1--3.5
• Yellow 5650---5750 5.3--5.2 3.5--3.45
• Orange 5750---6000 5.2--5.0 3.45--3.3
• Red 6000---8000 5.0--3.7 3.3--2.5

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Some equations you need to know
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• ? c / v
• and
• E hv
• So.
• E hc / ?
• And
• ? h / mv

• When
• ? wavelength in m
• c speed of light, 3.00E8 m/s
• v frequency in Hz
• (cycles/sec or s-1 or 1/s)
• E energy in J
• h Planks constant, 6.626E-34 Js
  Joule(seconds)
• m mass of particle in kg

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What the h? Plancks Constant
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• When metals are heated, they glow
• 1800s- physicists were trying to determine the
  relationship between the color (wavelength) and
  intensity of the glow
• Max Planck (1900)- energy can be released or
  absorbed only in little chunks (packets) of
  energy of some minimal size

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Max Planck and the h
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• The chunks of energy were dubbed quantum
  (fixed amount), which is the smallest amount
  that can be emitted or absorbed as EMR.
• Proposed E hv
• The energy (E) of a single quantum is equal to
  its frequency (v) times a constant

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Planck and the Nobel (Physics)
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• Planck determined that h 6.626E-34 J-s
• Energy is always released in multiples of hv
  (1hv, 2hv, 3hv, etc)
• h is so small that we cannot see the effects of
  this in our daily lives
• Analogous to
• Planck won the 1918 Nobel Prize in physics for
  his work

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Einstein Bohr Perfect Together
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Einstein (or Mr., Read, you decide), left Bohr,
above
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EinsteinThe Photoelectric Effect
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• Einstein discovered that one could cause
  electrons to be ejected from the surface of a
  metal if the energy of the light wave was strong
  enough
• He treated the light needed to do this as a piece
  of matter- a photon, if you will

• This ejection of e- is the photoelectric effect

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The Photoelectric Effect
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• Only light of a certain energy could knock off an
  electron from the metal
• Intense light of a weaker wavelength would not
  work, but even a low intensity of the correct
  wavelength would work
• (the energy of the light is transferred to the
  kinetic energy of the electron)
• Hmmm light acting as a particle and as a wave..

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The photoelectric effect
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• http//www.lewport.wnyric.org/mgagnon/Photoelectri
  c_Effect/photoelectriceffect1.htm
• http//www.xmission.com/locutus/applets/Photoelec
  tric.html

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Getting to Bohr.
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• Light of a given wavelength is monochromatic (one
  color)
• Most common EMR sources are polychromatic, but we
  see only one color

• These can be reduced to a spectrum when the
  different wavelengths are separated out

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Spectral Emissions
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• Continuous spectrum shows all colors of the
  rainbow

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• Bright line spectrum only certain wavelengths
  are visible (the rest do not appear at all)
• Different elements have different bright line
  spectrum when they are heated
• Na is yellow
• Ne is orange-red

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Line spectrum
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• Ne
• I2

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http//www.cartage.org.lb/en/themes/Sciences/Astro
nomy/Modenastronomy/Interactionoflight/AtomicAbsor
ption/AtomicAbsorption.htm
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Hydrogen Spectra
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Emission Spectra
Absorption Spectra
http//www.mhhe.com/physsci/astronomy/applets/Bohr
/content_files/section1.html
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http//www.cartage.org.lb/en/themes/Sciences/Astro
nomy/Modenastronomy/Interactionoflight/AtomicAbsor
ption/AtomicAbsorption.htm
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• Line spectra formation- go to..
• http//www.mhhe.com/physsci/chemistry/essentialch
  emistry/flash/linesp16.swf

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Bohr Model and Spectral Emissions
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• Bohr proposed that the emission of light energy
  from an (electrically or thermally) excited atom
  corresponds to the orbit of the electron around
  the nucleus of the atom
• That energy can only be achieved by being a
  specific distance from the nucleus

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What youve seen so far.
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Model of a Nitrogen (z7) atom
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Bohr Model and moving electrons
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• http//www.colorado.edu/physics/2000/quantumzone/b
  ohr.html

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Energy levels- Bohr Model
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• Electrons travel within set energy levels that
  have a particular energy associated with each
  level
• After all, the e-s are moving around the nucleus
• think KE here
• Each shell has a number
• Closest to the nucleus is n1
• For each successive level add 1 to n
• n2, n3, ect.

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Energy increases as the distance from the nucleus
increases
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Bohr Model and moving electrons
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• http//www.colorado.edu/physics/2000/quantumzone/b
  ohr.html

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Electron config in energy level
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SO
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• We know that the e--s are free to move around
  the nucleus
• They also can move from one energy level to the
  next (and fall) back when energy is added
• Move from ground state (home level) to a higher
  level (the excited state)
• Returning back to the ground state releases energy

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• This emission is how we see colors
• the wavelengths of EMR released from an atom when
  it has been excited by
• Heat energy
• Electrical energy
• Chemical energy
• Think glowing red hot metal, or fireworks

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Alsolife after Einstein and Bohr
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• We know that electrons have characteristics of
  both light (waves) and matter, so we say that
  they have a dual nature

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De Broglie
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• De Broglie proposed that an electron moving about
  the nucleus had a wave-like behavior, so that
  they it has a particular wavelength associated
  with it. This wavelength depends upon the mass
  and velocity of the electron.
• ? h / mv
• mv the momentum of the particle

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• This matter-wave idea applies to all matter, not
  just to electrons
• However, the mass is so large, and the wavelength
  so small, that we cannot see it in macroscale
  objects
• This matter-wave theory led to applications like
  the electron microscope

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De Broglie wavelength
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HeisenbergThe Uncertainty Principle
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• We cant determine information about small scale
  objects the same way we can for large scale
  objects
• Case in point a ball rolling down a ramp- we can
  get position, direction, and speed at the same
  time
• We cant for electrons
• Hence, the uncertainty principle

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Heisenberg, contd
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• It is inherently impossible for us to
  simultaneously know both the exact momentum and
  exact location of an electron
• This is because anything we do to determine the
  location or momentum of the electron moves it
  from its original path and location this cant
  be reduced past a certain minimal level
• We can know only momentum or location- not both
• We can talk probability of the location/ momentum
  of an electron

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Which brings us to this question
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• What the heck does all of this have to do with
  electron configuration and how matter behaves?
• On to electron configuration, courtesy of
  Schrödinger and company (enter math that well
  skip)
• Quantum theory

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EMR and the atom Part Deux
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Electron Configurations
http//imagers.gsfc.nasa.gov/ems/waves3.html
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What youve seen so far.
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Model of a Nitrogen (z7) atom
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Which is really not true- why?

• Because orbitals- the electron cloud are
• 3-D
• are not round in all most cases
• e- spread out as much as possible.

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The s orbital
http//www.sfu.ca/nbranda/28xweb/images/s_orbital
.gif
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p orbitals
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d orbitals
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d orbitals
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f orbitals
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General tutorials for electron configuration stuff

• some slides in this PowerPoint are from this site
  already
• http//www.wwnorton.com/chemistry/overview/ch3.htm
  
• See key equations and concepts (select from menu
  on the left), as well as the looking through the
  overview where to the tutorials are listed (links
  for just those are on the left, too)

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Quantum numbers
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